Liaison: Hazel Fitzgibbon
Usually diagnosed in young puppies, microphthalmia* literally means ‘small eye’. Due to a defect early in fetal development, the eye does not grow at the same rate as the rest of the head and therefore looks smaller than it should. Eyes may look a little sunken. Third eyelids can be prominent.
Microphthalmia itself will not stop your Samoyed from seeing. It is the ‘nasties’ that go with it that can be the problem. It is often associated with other defects (ocular dysgenesis). These may include defects of the cornea, lens, retina, or anterior chamber of the eye. There can also be coloboma, a cleft in a portion of the eye, such as the iris. Cataracts are often associated with microphthalmia and can cause partial to total blindness.
*Microphthalmia is often misspelled as micropthalmia on the internet.
Signs and Symptoms
This condition is apparent in pups once their eyes have opened. Affected eyes are smaller than normal and appear recessed. The third eyelid may be more prominent. One or both eyes may be affected.
This is a congenital condition (present at birth), being nondevelopment of the eye. In some breeds, it has been found to be inherited, often associated with “merle” coat coloring. The genetics have been well-studied in mice, where mutations in the regulatory gene MITF (microphthalmia-associated transcription factor) affect the development of pigment cells (melanocytes) and can lead to microphthalmia, deafness, and loss of pigmentation. The MITF gene in dogs has recently been identified and shown to be associated with white spotting or piebald coat coloring in several breeds.
Microphthalmia might also be inherited in Samoyeds, but this has not been determined. There are also references to pesticides and wormers causing the problem.
Related dogs with microphthalmia. In some other breeds, having both sire and dam with merle coat coloring is a risk factor.
It is visible to the naked eye. The third eyelid (the white bit in the corner) often looks larger than normal. Examination by a veterinary ophthalmologist, who will also examine your dog’s eyes thoroughly for other abnormalities, will give a definitive diagnosis. The examination is non-invasive, using light and magnifying lenses to examine and look inside the eye.
Note: Treatment of animals should only be performed by a licensed veterinarian. Veterinarians should consult the current literature and current pharmacological formularies before initiating any treatment protocol.
The basic defect can’t be treated. Associated complications, such as glaucoma, are treated as required.
The degree of visual impairment depends on the severity of the defect. If the eyeballs fill half of the openings, there is a 50% chance the puppy will be blind. If more severe, most puppies are blind. Vision can also be impaired by the associated defects, such as cataracts. Puppies with cataracts typically have some visual impairment because when the eye opens for the first time, daylight cannot penetrate the cataract and the retina is not ‘activated’ into proper operation. Sometimes cataracts improve over time, although their reabsorption may lead to leakage of liquefied lens material and inflammation. Sometimes they get worse. It is unpredictable.
Dogs are so good at using their senses of smell and hearing to compensate for poor vision that when your dog is in familiar surroundings, you may not even be aware of the extent of his vision loss. To assist your dog, keep his environment consistent. Don’t move the furniture, or if you must, make changes gradually. Routes for walks should be consistent.
Because it is a serious disease for both the animal and the owner and might be inherited, animals with microphthalmia should not be bred. If the parents or normal-eyed siblings are breed, it should be with great caution, as the genetics of microphthalmia have not been worked out.
Canine Inherited Disorders Database gives an overview on http://cidd.discoveryspace.ca/disorder/microphthalmia-ocular-dysgenesis.html
National Center for Biotechnology Information description of MITF gene: http://omim.org/entry/156845
Rothschild MF, Van Cleave PS, Glenn KL, Carlstrom LP, Ellinwood NM. Association of MITF with white spotting in Beagle crosses and Newfoundland dogs. Anim Genet. 2006 Dec;37(6):606-7. http://onlinelibrary.wiley.com/wol1/doi/10.1111/j.1365-2052.2006.01534.x/full
This is a well documented problem in humans and there seem to be dozens of web sites and help groups for them.
helps people whose dogs have lost all sight.
There are many of web sites for other breeds, but none specifically for Samoyeds. A number of these sites associate microphthalmia with merling and coat colours. Some also associate deafness with merling and microphthalmia. Merling has not been associated with Samoyeds.
OFA is the US overseer for heritable eye disease in dogs and has the US database.
The BVA is the overseer in the UK. Please note Samoyeds are not routinely eye tested in the UK. [http://www.thekennelclub.org.uk/health/health-information-and-resources/health-schemes-and-programmes/bvakc-health-schemes/bvakcisds-eye-scheme/]