Microphthalmia; ocular dysgenesis

What is ... ?: 

 Affected dogs have prominent third eyelids and small eyes which appear recessed in the eye socket (enophthalmos). A defect early in development results in the smaller than normal eye (microphthalmia).This is often associated with other eye abnormalities, including defects of the cornea, anterior chamber, lens and/or retina. Microphthalmia is also seen with coloboma - a cleft in a portion of the eye, particularly the iris.

Microphthalmia with multiple defects (ocular dysgenesis) is often seen in dogs with a merle hair coat with excessive amounts of white. The eyes are commonly different colours. Partial deafness may also be part of this syndrome. These dogs are frequently blind.

How is ... inherited?: 

In Doberman pinschers and miniature schnauzers, inheritance is autosomal recessive. The mode of inheritance has not been proven for other affected breeds. Microphthalmia with multiple defects (ocular dysgenesis) is a recessive trait in merle Australian shepherds.

What does ... mean to your dog & you?: 

 Microphthalmia may be associated with other minor or major eye abnormalities. Where the changes are mild, there is usually no visual impairment. With moderate microphthalmia, the eyeball fills about half of the opening. About 50% of these pups will be blind. Where the defect is severe, all of the pups are blind. In general, microphthalmia is evident as soon as a pup's eyes are opened. 

Pups with microphthalmia with cataracts will usually have some visual impairment. The cataracts may be progressive resulting in a worsening of vision, or they may mature and be reabsorbed, resulting in improved vision. This is unpredictable. In the process of resorption, liquefied lens material may leak into the eye causing inflammation.
With their acute senses of smell and hearing, dogs can compensate very well for impaired vision.  You may not realize the extent of your dog's vision loss, particularly in familiar surroundings. You can help your visually impaired dog by developing regular routes for exercise, maintaining your dog's surroundings as consistently as possible, introducing any necessary changes gradually, and being patient.

How is ... diagnosed?: 

 This condition is apparent in pups once their eyes have opened. Affected eyes are smaller than normally and appear recessed. The third eyelid will be more prominent. Your veterinarian will examine your dog's eyes thoroughly for other abnormalities. With ocular dysgenesis, vision is frequently impaired.

How is ... treated?: 

 There is no treatment for the structural defects. Complications that may develop, such as glaucoma, are treated as required.

For the veterinarian: 

 Ocular abnormalities that may be seen with ocular dysgenesis and merling with excessive white in the coat, include microphthalmia, microcornea, heterochromia irides, cataract, staphyloma, retinal detachment, irregular pupil, white to blue iris (albino), angle dysgenesis, iris coloboma, and blindness.

Anterior cleavage syndrome,or anterior ocular dysgenesis, has been seen in association with microphthalmia in Doberman pinschers and Saint Bernards. In addition to other ocular abnormalities as seen above, the anterior chamber, pupil and iridocorneal angle are not formed. The anterior uvea is continuous with the posterior cornea. Pups are blind.

Breeding advice: 

 Parents, normal-eyed siblings, and  affected dogs should not be bred.

Merling is inherited as a dominant trait. Heterozygotes for merling have merle or dappled coats and occasional eye abnormalities. Homozygotes have predominantly white coats and frequent eye abnormalities including microphthalmia. Due to the association of multiple defects with coat colour, selection towards a white or albino coat or towards excessive white in a merled breed (ie selecting for homozygotes) should be avoided.

What breeds are affected by ... ?