Resources

Information on Eye Diseases

Vision Loss in Dogs


Vision loss in your pet can be an emotional time for all family members. Therefore it is important that you are all aware of the problem and give yourselves and your pet time to adjust. The emotions that you may all go through are quite normal but you need to be aware that there is something you can do for your pet. Being blind is not a death sentence. It is just a new learning experience for the whole family. In fact you may get a lot of pleasure out of re-training your dog to cope with his/her blindness. It will be challenging but here are some tips to help you and your pet develop your relationship on a new level: Try different methods of announcing your presence when approaching your pet. Whistling, clapping your hands softly, wearing bells around ankles or wrists may assist in alerting your pet to your where-about's. Using verbal cues when around your pet will reassure him/her and assist with retraining. Words like “up” or “down” for stairs or “careful” when he/she approaches an obstacle. For blind dogs that are deaf special training devices can be obtained to assist when verbal cues won’t help. Scented perfumes and oils can be placed on the edges of furniture. This is particularly good to assist your pet to be able to “map” out the area especially if you need to move furniture around or are moving house. The garden can also pose a challenge for your pet. One solution is to plant your garden with highly scented plants or distinctive smelling mulch to help your pet move freely around the back yard. Different smells can allow your pet to “map” out the area, slowly regain his/her confidence and give him/her something interesting to investigate. Allow your pet play time. Give him/her toys which work on the other senses. Try toys that make noises, or balls with bells inside. Stimulate your pet by hiding food treats inside a Kong or ball. Use training aids such as the blind collar or hoop which will alert your pet to obstacles, particularly in new environments. Be aware of pools and cliffs or holes with sudden drop offs. Keep food and water bowls in the same area. Use matting which is textured differently from the surrounding floor, this will let your pet know that food or water is nearby. Have safe areas for your pet. Use designated bedding or matting which has a different feel from other areas in the house. Your pet will learn that this is an area they can go to feel safe and regain his/her bearings. Try using textured matting, such as the grass matting on the edge of stairs so that your pet can feel when to step off the steps. If stairs really pose a problem, build a ramp for him/her to use. When exercising your pet, have a couple of different routes that you use for walking. Once your pet has “mapped” out the route, his/her confidence will grow and eventually he/she will be taking you for a walk. Get your blind dog, a sighted canine companion. A recent programme on pay TV showed another sighted dog was of great benefit to a blind dog. But before making the decision to get another dog, always make sure it is going to be the right decision for your family. Another dog will increase the responsibility of all family members and another dog may not suit the personality of all blind dogs. If you like the idea of another canine companion, inquire with friends if their dog would like to be a regular visitor to the household, particularly while they are at work etc. Always remember to spend quality time with your special friend and be patient when training him/her. This is a challenging time for him/her too.




Cataracts in Dogs


What is a cataract?

A cataract is an opacity of a structure inside the eye called the lens. The lens is usually clear and transparent, and helps to focus an image onto the retina, at the back of the eye. The same process happens inside a camera, with the lens focusing an image onto the film in the back of the camera. Having a camera with a foggy lens is somewhat similar to having a cataract—both produce very poor images! In humans, cataracts are one of the most common causes of blindness, especially in

third-world countries.

What causes cataracts?

Many things can cause cataracts, and often we cannot be 100% certain of the cause in each and every case. Most cataracts seen in dogs are caused by genes inherited from their parents, but diabetes, injuries, inflammation, drugs and nutrition may also be to blame.

What are signs of cataracts?

Owners of dogs with cataracts usually report a deterioration in their pet’s eyesight. Poor eyesight may be noticed as an increase in ‘clumsiness’, a change in personality (lethargy or aggression), or a reluctance to go into the dark, among other things. Sometimes our clients notice a white area in their dog’s pupil (the black circle in the middle of the eye), or their referring veterinarian notices the problem during a routine physical examination.

What can we do for cataracts?

In the past, people have tried all sorts of medications to clear cataracts. With our current medical knowledge, we know that surgery is the only cure. This doesn't mean that your pet must have cataract surgery, as some cataracts do not affect vision enough to warrant the procedure.

You can discuss your pet’s suitability for surgery with one of our team members.

Why is cataract surgery recommended earlier rather than later?

Assessment and treatment of cataracts before they become too advanced is important for two reasons:

  1. We need to assess the retina (the light sensitive membrane at the back of the eye), to ensure it is normal. This can be done more easily when the cataracts are not too dense, enabling us to see the retina with specialised diagnostic examination instruments.
    If the cataracts are too dense we may need to do more specialised tests, such as ultrasound or electroretinography (ERG), to evaluate the structure and function of the back of the eye to ensure a successful outcome. These tests are often done on the same day that we intend to do the cataract surgery. If your pet fails either of these tests, then we may recommend that surgery not be performed as it will not improve vision for your pet.

  2. If left in place for too long, a cataract can cause inflammation inside the eye. Sometimes medication can control the inflammation, and help control the associated pain. In the long term, however, the inflammation within the eye may become so severe that glaucoma (increased pressure in the eye) and uncontrollable pain may occur. In these cases, cataract surgery will not be an option for improving vision.

Also, cataracts which have been present for some time can develop other problems such as opacity in the normally clear capsule surrounding the lens, or breakdown of the lens zonules which hold the lens in place. These secondary changes can reduce the chances of achieving the best outcome. Even if you decide not to have cataract surgery, regular rechecking by one of our eye specialists would be recommended to monitor the progression of the cataract, and the associated problems in your dog.

What does cataract surgery involve?

The surgical techniques used to remove cataracts in your pet are almost identical to those used in humans. The technique most widely used is called phacofragmentation, and uses ultrasound energy to break the lens into tiny pieces which are then sucked out of the eye. Most cataracts are removed through a small ‘key-hole’ incision 3-4mm wide in the top of the eye! Removal does not involve the use of a laser, as some people mistakenly believe.

In most cases, after the lens is removed, the capsule surrounding the lens is left intact so that an artificial lens (IOL) can be inserted to correct the close distance vision back to normal. Not all dogs are candidates for an artificial lens. The decision to place an artificial lens depends on various factors, and is usually made by the surgeon during the procedure. Modern implants are made of a foldable plastic, and can be inserted through the same small 3mm incision.

How successful is cataract surgery?

The success rate for cataract surgery in dogs has markedly increased over the last 10-15 years, mainly as a result of new research and improved surgical techniques. In general, our patients achieve good, long-term vision the majority of the time. As with all surgery however, it is impossible to give an unqualified 100% guarantee of success with no complications.

What are the most common complications?

The three most common reasons for a poor result after cataract surgery are:

  • ongoing inflammation in the eye

  • retinal detachments, and

  • glaucoma.

More rarely

  • spontaneous bleeding within the eye,

  • opacities in the lens capsule,

  • corneal disease.

It is very important to understand that some of these complications can result in blindness and/or loss of the eye due to uncontrollable discomfort. Usually the problems are not predictable and sometimes they do not occur immediately after surgery, often arising months or even years later. For this reason we recommend regular follow up visits after cataract surgery to try to identify these complications before they cause a poor outcome. These complications are similar to those seen after human cataract surgery.

Are there risks in having a general anaesthetic?

Although modern anaesthetics are generally very safe, very rarely complications and deaths can occur, and owners must accept this risk albeit very small. To minimise the chances of an anaesthetic complication, a detailed history of your dog’s previous and current medical problems is taken before surgery, and the patient is evaluated clinically for any possible risk factors. For animals over 7 years old, we recommend that your veterinarian perform preoperative blood tests. For dogs with heart or lung problems, a referral to a specialist may be recommended to assess the relative risk of anaesthesia. Modern anaesthetic agents and techniques are used during the cataract surgery, and the patient is constantly monitored during both the procedure and the recovery phase of the anaesthetic.

What happens after cataract surgery?

Usually your pet will be discharged from hospital on the afternoon of surgery. It is important to keep your dog quiet for the first two weeks afterwards, and limit exercise to strict leash walks, preferably with a chest harness (throat collars can increase the pressure in the eyes). Your dog should be not allowed to play with toys or balls, romp with other dogs, or travel with its head out of a car window. At first, you may be using topical medications up to 4 times daily. Over time the frequency of medication required decreases.

When we do send your dog home, it is essential that you use the medications as prescribed. Failure to do so, even for as little as a day or two, can result in uncontrolled inflammation and even glaucoma or other problems inside the eye.

The first rechecks are usually at one and three weeks after surgery. Subsequent revisits will depend on the progress of the case, but are usually at 6-12 monthly intervals.

When will my pet see after surgery?

If all goes well, your pet may have vision as early as the day after surgery. Some dogs may, however, take a few weeks to fully regain their vision due to the amount of post-operative inflammation present in the eye.

What is the cost of surgery?

The prices charged for cataract surgery reflect the costs of the highly specialised equipment used and the level of expertise required on the part of the surgeon. The disposable items and prosthetic lenses used during surgery can be expensive, and sometimes have to be imported from overseas. However, we are constantly striving to keep these costs within reasonable limits so that your pet can enjoy a better quality of life by being able to see again.

Our veterinary eye specialists will endeavour to give you as accurate an estimate of costs as possible before surgery. Please understand however that this is an estimate only and the final cost may vary slightly depending on circumstances at the time of surgery.

The estimated fee includes pre-operative tests where necessary, anaesthesia, theatre fees, surgical fees, disposable theatre items, drugs, and hospitalisation. The first two rechecks after cataract surgery are included in the estimate. After this time, a standard minimal revisit fee will usually apply. Further drugs prescribed at rechecks after surgery will also be at additional cost. In the unusual event of complications, we will always attempt to keep any associated additional costs as low as possible.

Please feel free to discuss any further questions you may have about cataract surgery with Animal Eye Services.




Progressive Retinal Atrophy


What is Progressive Retinal Atrophy?

Progressive Retinal Atrophy (PRA) is a common term used for a group of inherited diseases that cause loss of vision due to degeneration of the retina. It is seen in many breeds of dogs, but most commonly in Cocker Spaniels, Poodles, Australian Cattle Dogs, Silky Terriers and Labradors.

Clinical signs

The disease causes gradual blindness, first affecting vision in dim light (night vision) and eventually, resulting in complete blindness many months or years later. Towards the end of the disease the affected eyes develop cataracts.

The first sign noticed by owners of pets is poor vision in dim light. Their dog may be reluctant to go outside in poor light, may seek out brighter light and may actually bump into things at night. Some dogs may show an increased green reflection of their eyes in artificial light.

With time the day vision begins to deteriorate and cataracts start to develop. These are seen as a white opacity in the centre of the pupil. The cataracts exacerbate the loss of vision because they prevent light passing through the eye to the retina.

Since the vision loss is so gradual, most owners don't notice a problem until the blindness has progressed to a severe end stage.

Treatment of PRA

Sadly, there is no known treatment for PRA at this time.

The cataracts that often also develop in association with PRA are usually not treated as their removal will not result in an improvement in vision. Eventually the cataracts, visible as white opacities in the centre of each eye, can cause other conditions such as uveitis (inflammation of the iris) and even glaucoma (high pressure in the eye) Usually treatment of the earlier stages of the inflammation with cortisone drops will prevent the development of later glaucoma.

Diagnosis of PRA

Depending on the stage and severity of the disease a combination of clinical exam, Chromatic PLR testing and/or electroretinogram (ERG) can be used.

Prevention of PRA

Genetics play a vital role in the disease and therefore, individuals related to an affected dog should also be examined for PRA with an eye examination. PRA is generally but not always inherited as an auto somal recessive trait. This means that the condition is passed on from both parents.

Since the mid 1990s DNA blood tests have become available to detect affected dogs and parents who may be genetic carriers of the condition.




Lens Luxation


The lens is held in its normal position behind the iris and pupil by tiny strands called "zonules". Disruption of the zonules can cause the lens to move out of its normal position (luxate). When a lens is only partially held by some zonules, it is referred to as a subluxated lens. When a lens is no longer held by any zonules, it is called a luxated lens.

Two general categories of lens luxation are defined according to whether or not the luxation was the first eye problem (primary lens luxation) or whether it was caused by another eye condition (secondary lens luxation). Primary lens luxation is seen more commonly in certain breeds (e.g. Jack Russell Terriers, Miniature Fox Terriers, Tenterfield Terriers and Cattle Dogs) where the defective lens zonules weaken and break over time. Trauma to the eye or head can also cause lens luxation, although it is not usually the primary cause. Trauma severe enough to cause lens luxation usually also causes other obvious eye problems.

Lens luxation can be secondary to other eye diseases such as glaucomaor uveitis. Elevated pressure inside the eye (glaucoma) or inflammation inside the eye (uveitis) can cause the zonules to weaken and the lens breaks free. Interestingly, a luxated lens can also causeglaucoma. Sometimes when we see a patient with multiple eye problems for the first time, it is difficult to tell which problem came first: the luxated lens or another eye condition!

Treatment of a luxated lens depends on the general health of the eye, the position of the lens, and whether or not the patient can still see out of the affected eye. If the lens is loose but is still behind the iris, we sometimes use medications which constrict the pupil in order to trap the lens in its proper position. If the lens has moved in front of the iris, then surgery may be recommended to remove the lens. Occasionally we will be able to “couch” the lens back behind the iris if conditions within the eye allow this. The lens can then be trapped behind the iris where it is less likely to cause complications. This is done by constricting the pupil with special prescription eye drops. These drops need to be used FOREVER though, missing a single dose could allow the pupil to dilate and the lens to slip back into the front chamber of the eye again.

Lens removal or “lensectomy” is done under general anaesthesia with the use of an operating microscope. An incision is made in the edge of the eye and the lens is removed using a small spoon shaped device called a lens loop, or a probe with a frozen tip is inserted into the eye to capture the lens. The lens adheres to the end of the probe in the same way your tongue would stick to a frozen lamp post in the winter! The surgeon then pulls out the lens in one piece. The corneal incision is sutured closed. Without a lens, the patient is still expected to be visual. Their ”up close” vision is rather fuzzy, though, as they cannot accommodate to nearby objects.

Sadly, despite everyone’s best intentions and efforts, a fair proportion of eyes affected by lens luxation will end up blind and/or have to be removed due to uncontrollable pain. This can be the case even when emergency surgery is performed.




Glaucoma


Glaucoma is "an increase in pressure in the eye with a loss of vision". The disease is quite painful in most cases, especially when the eye pressure is very elevated.

The signs of glaucoma include:

  • redness
  • cloudy eye
  • tearing
  • loss of vision
  • an enlarged eyeball
  • unusual aggressiveness
  • lethargy
  • loss of appetite

The normal physiology of the fluid in the eye calls for the fluid to be made in one structure behind the pupil (ciliary body), travel through the pupil, and exit out the space between the cornea and the iris. When the fluid cannot properly drain from the eye, the pressure in the eye is increased. An analogy would be a kitchen sink -- if the drain is open and the water is running, there is no problem. However, if a plug is placed in the drain and the water keeps coming, then the sink fills up with water and overflows! Some patients have primary glaucoma where there is no concurrent disease but some secondary causes of glaucoma include: inflammation, trauma, and tumours. All of these factors can obstruct the drainage of fluid from the eye.

Glaucoma is an ophthalmic emergency and must be treated immediately. If the pressure remains elevated for even a few hours, permanent vision loss occurs. The disease is difficult to treat but several options are available depending on whether the patient still has vision, the specifics of the patient, financial considerations, etc. Some of the options include: medical management with drugs, laser surgery, surgically placed drainage tubes, removal of an end stage blind painful eye or replacement with a cosmetic prosthesis. There are pros and cons to each of these treatments, and the options will be discussed with the client after initial examination, consideration of the possible duration and severity of the glaucoma and the chances of getting vision back again.




Uveitis


Uveitis refers to inflammation of a structure inside the eye called the uveal tract. The uveal tract lines the inside of the eye. It is the only structure within the eye containing blood vessels. At the front of the eye it is called the iris, at the back of the eye it forms a structure under the retina called the choroid. A specialised part between the front and back is called the ciliary body and produces fluid inside the eye.

When the uveal tract become inflamed, blood cells and debris leak out into the internal fluid filled chambers of the eye, resulting in cloudiness and loss of vision in severe cases. Clinical signs of uveitis include cloudiness of the cornea, redness around the edge of the eye, tearing, squinting, bleeding into the eye, and loss of vision.

Uveitis in the dog and cat can have many different causes, these will be discussed with you in consultation.

Severe uveitis can result in vision threatening complications such as cataractformation, adhesions of the iris to the lens or cornea, retinal disease, and glaucoma. Treatment for uveitis is aimed at reducing the inflammation and preventing the complications. The treatment protocol will vary for each patient.




Dry Eye


A healthy cornea and conjunctiva at the front of the eye is highly dependent on the presence of a healthy tear film. The normal tear film is made up of three layers:

  1. The outer lipid layer produced by the Meibomian glands within the eyelids.

  2. The aqueous (watery) layer. This represents over 95% of total corneal thickness, The watery component of the tear film is produced by lacrimal gland, a small gland which is found deep in the tissues behind the outer upper eyelid.

  3. The mucous layer. This layer enables the tear film to “stick down” to the surface corneal cells.

There are many causes of dry eye including congenital disorders (puppies), infections (canine distemper virus), drug-induced (sulfa antibiotics), and removal of the tear gland of the third eyelid ("cherry eye"). The most common cause is thought to be autoimmune destruction of the lacrimal gland by immune system cells: the immune system inappropriately attacks the cells in the gland which produce the watery component of the tear film. The disease is seen very commonly in certain breeds such as the Cocker Spaniel, Shih Tzu, Lhasa Apso, Bulldog, Schnauzer, and West highland White Terrier.

The clinical signs of dry eye include:

  • heavy mucus production

  • redness

  • rubbing at eyes

  • cloudy eyes

  • corneal ulcers

  • general lethargy

Many dogs have a history of having been treated for recurrent “conjunctivitis” with various anti inflammatory/antibiotic ointments or drops. After an extended period of dryness, the surface of the eye (cornea) begins to accumulate dark scar tissue and blood vessels – unfortunately to the point of blindness in many patients.

Our treatment goals for dry eye include stimulation of tears, lubrication, and decreasing the scar tissue. Cyclosporine or Tacrolimus are the preferred drugs for inhibiting the immune attack on the glands as well as stimulating natural tear production. It is important to understand that if you skip a dose or run out of the medication, they dry eye signs will immediately recur. In addition, it is crucial that you have your dog checked as directed to monitor treatment success.




Prolapsed Gland of the Third Eyelid "cherry eye"


When the tear gland of the third eyelid pops out of position, it protrudes from behind the eyelid as a reddish mass. This prolapsed tear gland condition is commonly referred to as "cherry eye". The problem is seen primarily in young dogs, and often in certain breeds such as the Cocker Spaniel, Lhasa Apso, Shih-Tzu, Poodle, and Bulldog.

Despite its appearance, cherry eye itself is seldom a painful condition. However, the longer the tear gland is exposed, the more likely it will come irritated and inflamed. If your dog rubs at the eye, it could cause the gland to bleed or become infected. Furthermore, the function of the tear gland could become compromised if the gland is exposed for long periods of time.

To correct cherry eye, surgical replacement of the gland is necessary. This treatment is superior to a somewhat older technique of surgically removing the gland. The gland of the third eyelid plays an important role in maintaining normal tear production. We now know that dogs who have had the tear gland removed are predisposed to developing Dry Eye Syndromelater in life. Dry Eye Syndrome is uncomfortable for the patient, and requires the owner to administer topical medications several times a day for the remainder of the patient's life. To avoid this condition, it is preferable to tuck the tear gland back inside the third eyelid, where it can continue to function normally.

The procedure used to correct cherry eye is called a "pocket technique". In this procedure the gland is pushed back into a small pocket on the back surface of the third eyelid, and the pocket is sutured closed.

In many cases there is an element of cartilaginous deformation associated with the third eyelid anatomy. In severely affected animals it can be almost impossible to achieve a 100% normal looking alignment of tissue after surgery.




Entropion


Entropion is an inward rolling of the eyelid. The problem is most common in the Shar Pei, Chow Chow, Bulldog, Retrievers, Rottweiler, and Mastiffs. Although the exact genetic pattern is usually not known, the problem is most likely caused by many genes that are responsible for the overall head and face conformation. Therefore, we recommend that you do not breed animals affected by entropion since the problem can be passed to the offspring.

When the eyelids roll in, the hair on the outside of the lid rub on the surface of the eye and cause corneal irritation. In some patients, entropion leads to corneal ulceration.

Common symptoms associated with entropion include squinting, tearing, and rubbing.

The treatment for entropion is surgery to remove some skin and muscle along the eyelid margin. This is cosmetic surgery and after reconstructing the eyelid, the lids should look normal. The incision is closed with tiny absorbable sutures and you shouldn't be able to see a scar at all.

The permanent surgery is usually performed after the age of 10 months. Usually only one surgery is required but since the problem occurs in growing patients, we might have to perform further surgery when the affected dog is an adult. Fortunately, about 95% of patients require only one surgery. After the surgery, your dog should not be shown or bred since the problem is considered inherited in most breeds.




Disorders in Brachycephalic Dogs


Flat nosed dogs such as Pugs, Pekingese, Shi-Tzus are commonly seen at Animal Eye Services. These dogs get numerous eye problems because their eyes tend to sit on the front of the skull without the benefit of protection by a deep boney socket as seen in other breeds with longer skulls.

There are several problems which arise from this conformation:

  • Many have medial lower eyelid entropion which results in chronic irritation of the cornea by hairs from the eyelid and the development of a pigmented film over the cornea.
  • Often their eyelid circumference is much larger than corneal circumference resulting in exposure of the tissues around the edge of the eye. These dogs can have a greater tendency to globe proptosis i.e. traumatic prolapse of the eyeball out between the eyelids and this can have catastrophic consequences for the eye i.e. tearing of the muscles around the outside resulting in inability to move the eyeball, and tearing of the optic nerve at the back of the eye resulting in permanent blindness.
  • Often the exposure of the eyeball can result in failure to close the eyelids properly over the cornea, especially whilst the dog is sleeping resulting in dryness and secondary corneal disease.

The best treatment for preventing the long term problems associated with the brachycephalic conformation is a procedure known as a permanent medial canthorrhaphy. This procedure involves removing a small section of the upper and lower eyelids at the inside corner of the eyes and resuturing the eyelids together again resulting in a smaller eyelid margin circumference and correction of the medial lower lid entropion.




Hypertense Retinopathy in Old Cats


Hypertensive retinopathy is a condition where high systemic blood pressure (hypertension) causes secondary retinal detachments or retinal haemorrhages. The problem tends to occur most frequently in elderly cats, and results in sudden blindness.

The retina normally lies flat against the back of the eye and contains cells (called rods and cones) which detect light, converting light stimuli into electrical impulses which are then transmitted to the brain for visual processing. When the retinas detach from their normal position, they cease to function and the patient becomes blind. Although immediate reattachment of the retinas can sometimes restore vision, cats' retinas degenerate quickly so in many cases by the time the diagnosis is made, the prognosis for vision is poor. Often retinal haemorrhages i.e. bleeding from small blood vessels in the retina can occur as well.

Since the hypertension caused the retinas to detach, treatment and control of the hypertension can help to achieve at least partial reattachment of the retinas. Unlike humans, high blood pressure in cats and dogs is not caused by poor diet. Instead, hypertension in animals is usually secondary to another problem such as kidney disease, heart disease, cushing's disease or thyroid disease. Treatment for hypertensive retinopathy usually involves an investigation into the possible underlying diseases responsible for the hypertension as well as medications to control the high blood pressure.




Corneal Endothelial Disease


CORNEAL ENDOTHELIAL DISEASE IN DOGS

Endothelial disease causes oedema or excess fluid in the cornea. To understand what is
going on a microscopic level it is important to understand the normal microscopic anatomy
and function of the cornea.


The cornea consists of three layers:


* EPITHELIUM: the outer layer of the cornea represents approximately 10% of the total
thicknesss. It consists of three layers of cells and is the outer protecting coat for the cornea.

* STROMA: the middle and thickest of the three layers forms around 90% of total thickness.
It is composed of hundreds of layers of collagen laid down in very regular sheets. Between
the collagen fibres is a ground substance (water and chemical compounds called GAGS)
which is osmotically active, ie water from inside the eye can be"sucked" into the corneal
stroma where concentration of these chemicals is higher.

* ENDOTHELIUM: is a single layer of cells on the inside of the cornea. The cells are laid
down in a very regular array like a mosaic of hexagonal shaped tiles. The endothelial cells
have little pumps in their membranes which normally move water out of the corneal stroma
back into the front chamber of the eye. Endothelial cells cannot regenerate - the cells present at birth remain throughout life but may degenerate with age.

The endothelium will continue to function normally until the density of the cells on the
endothelial surface gets below a certain critical level. The overall effect of this is a net
movement of water into the cornea. The water gets between the collagen layers in the stroma causing abnormal bending of light and a whitish blue opacity will appears as the stromal oedema develops. When the problem gets advanced, water can break out through the corneal epithelium, the outer layer causing painful chronic superficial ulcers.

The endothelium can lose its normal function in a number of ways


* natural loss of endothelial cells and decline in density with age.


* some breeds of dogs eg Boston terriers, Chihuahuas, Springer Spaniels seem to have a
natural breed-related dystrophy which results in abnormal function at an earlier age than
other dogs.


* damage by inflammation: when the interior of the eye becomes inflamed, inflammatory
cells and proteins deposit on the endothelial surface and damage it causing loss of normal
water pumping function and oedema


* glaucoma: very high pressure inside the eye can damage the endothelium


Endothelial disease is a very difficult disease to treat in dogs as there are no simple solutions
to replace the abnormally functioning endothelial surface. Endothelial grafts are an emerging field in veterinary medicine, not yet widely available. There are few drugs which can help to reduce the oedema: at best these drugs will stabilise the problem. If the disease becomes end stage then two alternative procedures can be tried, but these never return the cornea to normal clarity:


* thermal keratoplasty: applying tiny multiple burns to the outer layers of the stroma to
create scars or adhesions between the collagen layers and reduce their water holding
capacity


* Gundersen flap: a very thin layer of conjunctiva is dissected from the edge of the eye and
pulled across the corneal surface. The blood vessels in the conjunctiva help to improve the
egress of water from the water from the cornea. The veterinary ophthalmologist will discuss
the appropriateness of each of these procedures in your dog's case.




SCCED (Spontaneous Chronical Corneal Endothelial Defects)


AKA. Indolent ulcer, Boxer ulcer, Non healing ulcer

A SCCED is a non healing defect in the outer layer of the cornea, known as the epithelium. The normal corneal epithelium is around 10-12 cell layers thick and is constantly being turned over. The epithelial cells have their origin at the edge of the cornea and move towards the centre and outwards towards the surface before they are shed as dead cells into the tear film. The epithelium sits on a membrane called the basement membrane.


A superficial ulcer is defined as a defect where only the epithelium is missing but the
basement membrane is intact. Normally there is strong adhesion between the cells at the
base of the epithelium (basal cells) and the basement membrane. In a normal healthy cornea
with the normal healing mechanisms present, even large superficial defects should heal
rapidly, commonly within 2 weeks. These defects normally heal by the basal cells "sliding"
across and sticking down firmly to the basement membrane.


Unfortunately in some breeds, most commonly the Boxer, Samoyed, Welsh Corgi and the
Staffordshire Bull Terrier (although they can be seen in almost any dog) these superficial
ulcers fail to heal or show protracted poor healing over long periods of time. Sometimes they
can appear to have healed then suddenly appear as a new ulcer again. In these breeds we
know that there is a defect in the way the epithelium sticks down to the basement membrane at a microscopic level. Unfortunately simple medication with antibiotic ointments will not heal these defects as the problem is not due to bacterial infection. Procedures such as simple debridement (rubbing the loose epithelium off) third eyelid flaps or sewing of the eyelids together to protect the surface seem to be ineffective in most cases.


To get these ulcers to heal we need to do something which mechanically interferes with or
damages the basement membrane at a microscopic level so that the migrating epithelium can be induced to stick down to the basement membrane. We will discuss various options with you ranging from simple outpatient type procedures such as basement membrane burring to more involved procedures requiring a general anaesthetic such as grid keratotomy and superficial keratectomy, with the goal of achieving rapid resolution of this very frustrating
corneal condition.




Distichiasis


Distichiasis is a condition where eyelashes emerge from the meibomian glands in the centre of the eyelid. These glands do not normally produce hairs. These "extra" eyelashes often rub on the surface of the eye and may cause irritation. Distichiasis tends to run in genetic lines of dogs, and is most commonly found in Staffordshire Bull terriers, American Cocker Spaniels, Shih-Tzus Tibetan Spaniels and Poodles. The severity of the problem and the needs for treatment vary from patient to patient. Some patients may have only a few distichia (abnormal hairs) on a single eyelid, while others may have several distichia present on all eyelids. Although some patients live their entire lives without being bothered by their distichia, others require medical or surgical treatment to alleviate irritation caused by the hairs rubbing on the cornea. Signs of distichiasis include: redness squinting discharge rubbing at the eye Sometimes distichiasis can cause corneal ulcers or erosions where the hairs touch the surface of the eye. Clinical signs of corneal ulcers are similar to those of distichiasis: redness, squinting, discharge, or rubbing at the eye. Since corneal ulcers can also occur in patients that have no distichiasis, it can sometimes make determining the significance of the distichiasis difficult. The location of the ulcer and the distichia help us decide whether the distichia are the underlying cause of the ulcer. Temporary relief may be provided by pulling out the abnormal hair in the exam room, but these lashes almost always grow back. Topical ointments may be used to help lubricate the eye and protect it from the hair. If clinical signs persist, cryosurgery can be used to treat distichiasis. A liquid nitrogen or nitrous oxide probe is applied to the eyelid to kill the hair producing cells in the base of each Meibomian gland follicle and prevent the distichia from growing back. Although cryosurgery will prevent the distichia from growing back in the same area, there are about sixty places along each lid where new distichia could potentially emerge. Therefore, while surgery fixes the immediate problem, it is possible that the patient could have a future distichiasis problem if new distichia grow from other areas on the eyelids.





Information for Dog Breeders and Owners

Eye Certification for Purebred Dogs


Animal Eye Services provides eye certification for pure breed dogs. A thorough examination of the eye is performed, usually after drops to dilate the pupil have been applied. A report is provided outlining any abnormalities found and their significance with respect to effects on vision and their heritability. Why have eye certification? Eye certification is important for breeders as it helps to prevent the breeding of purebred dogs which have known genetic eye diseases. Some of these diseases can be both blinding and/or painful to the dog. Eye certification has been offered for some time throughout the world for breeders of purebred dogs. There are various national eye certification schemes in existence in USA (Canine Eye registry Foundation) in the UK, Europe and Scandinavia. Dr Bernays is a panellist for the Australian Canine Eye Scheme (ACES), a certification scheme modelled on schemes in Europe and North America. ACES was started in Australia to standardise the recognition and reporting of hereditary eye diseases in purebred dogs. To learn more about ACES, visit the ACES information page on the Australian Veterinary Association website. Procedure for eye certification Please turn up approximately 20 minutes before your appointment so that drops to dilate the pupil can be given. Pupil dilation is important so that the structures in the back of the eye can be examined carefully. Please make sure your dog has a microchip inserted for positive identification and bring your kennel club registration papers when presenting for eye certification.




Genetic vs Congenital Disease


What is a genetic disease? Genetic disease (= “heritable”, “inherited”) is a disease whose underlying basis is due to action of a gene or several genes acting to produce the defect. Genes in general are the biological code for the production of different types of proteins. Some proteins such as collagen are structural proteins while others are enzymes which facilitate various chemical reactions in the body. Very few eye diseases which occur in dogs have been identified as definitely having a genetic cause. In general most of the retinal degenerations seen in dogs are now known as having a genetic cause. The defective gene codes for an abnormal variant of an enzyme involved in the complicated cascade which converts the energy of light into electrical impulses. The end result of the defective gene is that the light receptor cell dies and the retina degenerates. Many cataracts are also suspected to have an underlying genetic basis but this is not yet proven. There are a number of well known genetic cataracts in laboratory animals such as rats where the outcome of breeding specific individuals together is highly predictable. Our approach is to assume a cataract to be hereditary unless another specific cause is identified eg trauma, unrelated intraocular inflammation or specific metabolic diseases such as diabetes. Other diseases such as entropion are more difficult to describe as being truly genetic (i.e. the action of specified genes) but the abnormality usually results from the breeding together of animals with poor conformation where this poor conformation predisposes to the eye disease. Eye certification can still identify poor conformational types which when bred together might result in the abnormality. The heritability of this poor conformation may be very complex involving the action of many different genes often acting in different ways to produce the final result. Some of these diseases where we are unable to put the title “genetic” to them are still described as having a “breed predisposition” i.e. the disease is seen at higher incidence in the breed than the general population at large. What is a congenital disease? Congenital disease means that the problem is present from birth. Congenital diseases may or may not be genetic. Where the disease is not genetic it may be the result of an insult to the embryo or foetus which occurred at a very specific time during in utero development. Had the insult occurred a few days either side of this time then the defect might not have occurred.




Phenotype vs Genotype


Phenotype refers to the outward appearance of the structure. Phenotype may be the result of either genes or effects of the environment. Genotype refers to the actual genes acting on that structure. The most simple way in which genes operate is on a dominant-recessive basis. Usually the dominant gene codes for the normal condition while the recessive gene is regarded as a variant which codes for the abnormal condition. The genes are found in the cell nucleus on structures called chromosomes which occur in matching pairs. Pairs of genes have a very well defined location on each of a specific pair of chromosomes. This position on the chromosome is known as a locus. In the classic situation the locus can have either a dominant or a recessive gene. Where two of the same type of gene i.e. dominant or recessive are found on matching chromosomes the animal is said to be homozygous for that gene. Where the two different variants i.e. a dominant and a recessive gene, are found at the locus on each of the chromosome pair then the animal is said to be a heterozygote. Heterozygotes are sometimes called “carriers” i.e. they carry the faulty gene on one chromosome but because there is a dominant gene on the other chromosome the normal phenotype is expressed. The abnormal phenotype is only seen when the animal is homozygous recessive for the condition. (i.e. has two recessive genes on each of the pair of chromosomes). Occasionally the defect is suspected to be due to the effect of the dominant gene rather than the recessive gene in this case only breeding homozygous recessives together will prevent the abnormal phenotype from occurring. There has been an explosion in our understanding of the molecular basis for many genetic diseases in man in the last 10-20 years. This explosion is now starting to occur in the canine world especially in our knowledge of genetic retinal diseases in dogs. Many retinal degenerations which only become apparent in middle age in susceptible breeds can now be identified by DNA testing at the puppy stage. In many of the diseases carriers can also be identified as well so this should make things easier in future. Unfortunately many ocular abnormalities still do not have an identifiable genetic cause. Therefore eye certification (i.e. examination by a qualified veterinary ophthalmologist) is still the only way we have at present to potentially identify breeding stock with a given abnormality and make decisions about whether they be bred or not, assuming the problem might be caused by a genetic defect. The effect of the abnormality on vision is probably the most important factor which is taken into consideration when a recommendation is made as to whether the animal should be prevented from breeding. In the rest of this section are some of the more common abnormalities of the eyes, with some general remarks about their cause and possible heritability. These abnormalities are covered in more detail in Information on Eye Diseases.




ProgressiveRetinal Atrophy (PRA)


Progressive Retinal Atrophy (PRA) is by definition a genetic condition resulting in degeneration of the retina and blindness in affected dogs. There are many different types of PRA with different modes of inheritance and different ages of onset but the most common type is seen in middle aged dogs of affected breeds and is due to a recessive gene. Classic breeds for PRA include the Miniature and Toy Poodles, Cocker Spaniels, Labrador Retrievers, Golden Retrievers and the Australian Cattle Dog. A number of different genes have been identified to date, the most common is the prcd or progressive rod-cone dysplasia gene. The first sign observed is usually night blindness with poor visual function in low light conditions progressing variably over months to years to complete blindness. There is no treatment. Traditionally there was no way to diagnose this condition until the dog developed the condition in middle age by which time it was probably towards the end of its breeding life. This made the culling of affected breeding stock difficult with resultant continuing propogation of the gene. There has been an explosion in the development of DNA blood tests in the last 10 years meaning now that in many breeds we can identify affected individuals and carriers at an earlier age. In some breeds such as the miniature and toy poodle and the miniature schnauzer there is more than one gene suspected as a cause of the condition and there may only be a DNA test for one of the genes.




Cataracts


A cataract is an opacity or cloudiness of the lens. The lens is found inside the eye behind the iris and in front of the retina. It is ovoid in cross section and was developed in evolution as a means of bringing into focus on the retina, structures close to the eye. In younger animals the lens has the ability to change shape to accommodate so that the eye can focus on objects at near or far distance. Many causes of cataracts have been identified. These include genetic, nutritional, metabolic, traumatic and post-inflammatory. Drug induced cataracts have also been seen in laboratory animals and are suspected to occur in other species as well. Steroid (“cortisone”) induced cataracts are seen in man but have not been suspected in dogs. Not all cataracts are complete and in many cases only part of the lens is involved. In many of these cases the change may not be progressive over time, however if the cataract matures the eye will become blind without cataract surgery to restore vision. Juvenile cataracts are first seen while the dog is young and are seen in a number of breeds. These cataracts usually mature early and cause blindness. This type of cataract is strongly suspected to be heritable. Another type of cataract seen in young dogs is the nuclear cataract: this type of lens is seen in the nucleus or the centre of the lens which is the earliest part of the lens to form embryonically. These cataracts usually reflect an insult during embryonic development and may not necessarily be heritable. They are often accompanied by other ocular abnormalities such as microphthalmos (undersized eye) and retinal dysplasia (abnormal structural development of the retina).




Entropion


Entropion refers to a disorder where the eyelid margin rolls in and irritates the surface of the eye. Perhaps the most common type of entropion seen involves the lateral lower eyelid or lateral canthus (where the upper and lower eyelids meet at the outer edge of the eye). Entropion can occur because of excess skin around the eyes or where the eyelid margin is too large for the size of the eyeball. Another factor which has also been suspected is inappropriate tension in the ligament at the lateral canthus resulting in pulling in of the eyelid at the canthus. While entropion does not generally cause blindness, it results in considerable discomfort for the dog and needs to be surgically corrected often at great cost to the owner.




Distichiasis


The term distichiasis refers to abnormal hairs which arise from the eyelid margin. Normally the eyelid margin is identified by small openings of ducts leading from glands deep within the eyelid. These meibomian glands are responsible for producing lipid for the surface of the tear film and are modified sweat glands. Normally they do not contain hair producing cells, but occasionally something goes wrong in embryonic development and hairs grow from these glands. The hairs are not always but usually irritating to the surface of the eye because they stimulate pain receptors in the surface of the cornea. A common sign of distichiasis is a watery discharging eye. In some dogs such as the Staffordshire Bull Terrier the hairs can be very stiff and the discomfort they produce can cause continuing spasm of the eyelids and eventually entropion secondary to the chronic spasm. In other breeds, such as the American Cocker Spaniel the hairs might be quite fine and will not necessarily cause significant irritation but might still stimulate excessive tearing.




Persistent Pupillary Membrane (PPM)


During the development of the eye, the front or anterior chamber of the eye is filled with a primitive embryonic tissue called the pupillary membrane. As this tissue disappears the pupil forms. Normally the pupillary membrane totally disappears but occasionally remnants of the structure remain in the eye as strands bridging the iris, or strands which travel from the iris across to the lens or cornea. In some breeds such as the Basenji or the English Mastiff they are known to be heritable. The heritability is not known in most other breeds but the condition rarely causes vision problems unless the strands cause extensive opacification of the lens or cornea. Usually the recommendation is that the breeder can decide if he or she will or will not breed dogs with PPMs (ie breeder option).




Persistent Hyperplastic Vitreous


The vitreous is the clear jelly like mass in the posterior chamber of the eye which fills the space between the lens and the retina. The vitreous goes through three phases in its development with formation of the primary, secondary and tertiary vitreous respectively. The primary vitreous forms as a large blood vessel which starts from the back of the eye and grows forward towards the lens. At the back of the lens this vessel, the hyaloid artery divides many times to form a network of blood vessels around the lens, known as the tunica vasculosa lentis. These blood vessels subsequently disappear before birth. Sometimes these blood vessels fail to degenerate, remaining in the eye after birth to form a large vascular plaque over the back surface of the lens. This condition is known as a persistent hyperplastic primary vitreous. This disease is suspected to be heritable at least in the English Staffordshire and the Doberman in which the condition was first described. It can cause vision problems but most cases are operable to restore vision. Since this is a vascular structure there is some risk however of haemorrhage within the eye during surgery.




Genetic Testing for Eye Diseases in Dogs


There has been an explosion in our understanding of the gene mutations which cause inherited eye disease in dogs over the last 10 years, principally as a result of the work of researchers at the Baker Institute for Animal Health at Cornell University in the USA and more recently the Animal Health Trust and Cambridge University in the UK. These DNA mutations can now be tested for by Optigen, the commercial arm of the Baker Institute and the Animal Health Trust and tests provided by both these institutions can now be performed by a Melbourne based company Genetic Technologies Ltd to remove the need to send samples overseas.





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