Ocular Disease
Ocular Hereditary Diseases
By M. Grauwels, DVM, MS, Dipl. ECVO
A hereditary disease is a genetic problem. It affects the genes of all the body cells and is perpetuated from generations to generations.
The hereditary disease can be present at birth; it is then called congenital and hereditary. But all congenital abnormalities are not necessarily hereditary.
A good number of hereditary ocular diseases are not congenital and will occur only during the normal course of the dog's life.
A yearly eye examination done by a certified veterinary ophthalmologist will allow:
- for the breeder to receive for each of his/her dogs a registration form
valid for one year stipulating the eye condition
exempt, temporarily, affected, suspicious-redo in 6-12 month
When the dog receives the title "exempt" it means that the eye
examination does not reveal a disease but in regards to its genes,there are two possibilities: - he is completely disease free: two normal chromosomes
- he is a carrier of the disease: on one of the two chromosomes, the disease is present and the animal will transmit the disease to the future generations.
- to uncover diseased animals, that is those showing active signs
of the
disease. - for the breeder to remove the active carrier from his/her breeding program as well as some of its related offspring carrying the recessive trait and who can be traced back to the actively affected dogs
- to inventory the problems by race and country since the same breed does
not necessarily carry the same ocular hereditary diseases in different
countries or different continents. - for the parent breed club to study the actual problem(s) and establish the proper guidelines and principles to maintain the breed in the best possible health.
This eye examination must be done in the dark after dilating the animal's pupils and with the help of an indirect ophthalmoscope and a biomicroscopic slit-lamp.
In the Coton de Tulear breed, the following hereditary diseases have been found:
1. Absence or narrowing of the lachrymal duct(s)
When the opening of the lachrymal duct at the level of the lid margin(s) is absent or too small, tears run on the dog's face. In some cases surgery can resolve the problem.
2. Abnormal or Extra Eyelashes (Distichiasis)
When extra eyelashes grow in atypical places from the lid margin(s) or inside the eyelid, those lashes will irritate the cornea and the conjunctiva. Electrolysis is the choice treatment.
3. Persistent Pupillary Membranes (PPS)
The very thin blood vessels closing the pupil in the foetus will have completely disappeared when the puppy reaches 6 weeks of age. Sometimes, some of these blood vessels remain. They are called PPM.Only the PPM adhering to the cornea (C) and/or lens cause troublesome cloudiness (opaqueness). There is no treatment.
4. Cataract
All cloudiness (opaqueness) of the lens is called a cataract. It can be seen in one or both eyes. The cloudiness can affect the whole lens or only a part of it. The prudent approach is to assume that cataracts are hereditary except in known cases such as injury, a PPM, diabetes.... Surgical removal of the clouded lens is well known.
5. Retinal Dysplasia (RD)
The retina is a thin, delicate membrane that lines the back of the eye, and actually is an extension of the optic nerve. The retina receives the light and converts it in electrical signals transmitted via the optical nerve to the brain. In the brain those signals are "transformed" in images. This phenomena is called vision. The retinal development is a highly complex one. Prenatal malformations can occur either by heredity or by factors such as infections, radiation traumas, deficiencies and medications.
Retinal Dysplasia is an abnormal development of the retina because of its two layers not fitting together correctly. This leads to 3 visual problems:
^^ folds (variable shape and length): normal vision or slightly affected
^^ geographic zone(s) with or without retinal detachment: this is the form
observed in the Coton de Tulear.
In its field of vision the dog has one or more "black
spots" thus producing
a loss and/or a visual alteration in limited areas
(corresponding to the
affected areas of the retina).
Total Detached Retina: loss of vision
This disease is congenital and hereditary. It can be detected by the age of six weeks and is present in approximately 50 different canine breeds. Lesions vary according to the breed. A simple autosomal recessive gene is usually suspected (except with Labradors and Samoyeds)
It goes without saying that an annual eye exam is of major importance to help us in the fight against certain hereditary eye diseases.
08/15/98 Translated by H. Lopatin
USACTC wishes to sincerely thank Dr. Grauwels for sharing this article with us as well as her dedication, help and continuous interest in the future of our breed.
Reprinted with permission of OSS Veterinary Clinic
Reprinted with permission from Love of Animals copyright l998.
November l998- volume 4, No.ll
Reprinted with permission of the Orthopedic Foundation of Animals