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What is Optic Nerve Hypoplasia and Micropapilla?

Both of these conditions are congenital anomalies or variations and can occur either unilaterally or bilaterally.  Upon ophthalmic examination, while both optic nerve hypoplasia and micropapilla in dogs may be similar in physical appearance, the results in terms of vision loss are quite opposite of each other.  The optic disc in the hypoplasia is abnormal and undeveloped and, therefore, can’t provide normal vision for the host while the micropapilla, a normal variation of the optic disc, is fully developed and will enable the host to see normally in both eyes.

Optic nerve hypoplasia is simply defined as a congenital condition in which optic nerves have not fully developed, resulting in vision loss. Micropapilla is defined as a congenital anomaly in which the optic nerve disc is smaller in diameter than normal but without vision loss.

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Symptoms of Optic Nerve Hypoplasia and Micropapilla in Dogs

These two conditions may look similar upon ophthalmic retinal examination but the similarity ends there.  Here are some of the symptoms you might notice in your dog:

  • Visual impairments which you might note in a child who doesn’t seem to see normally
  • Dilated pupils - One pupil may be larger than the other or both pupils may be larger than those of other canines in your household
  • Pupils that don’t respond properly or equally to light - For example, pupils are designed to constrict when subjected to bright light  
  • Pupils could be fixed (size remaining unchanged regardless of light situation)

Types 

The types of these optic nerve conditions are basically related to the degree to which vision has been affected and whether the condition exists in one eye or two.

  • Optic nerve hypoplasia - Can be unilateral or bilateral
  • Optic nerve hypoplasia - Vision loss can be mild, moderate or severe depending on the degree of underdevelopment of the optic nerve and if one or both eyes are affected
  • Micropapilla is simply a smaller than normal optic nerve disc but the functionality, the normal anatomy and the neurological connections are all present, giving the host normal bilateral vision

Causes of Optic Nerve Hypoplasia and Micropapilla in Dogs

Optic nerve hypoplasia, as noted above, is a congenital condition of underdevelopment which will cause some degree of vision loss in the host while micropapilla is a normal variation of the size and look of the optic disc which is fully developed and doesn’t affect vision in the host.  This condition seems to be inherited in some dog breeds while, in other animals, as in the case of kittens or calves for example, the condition seems to be related to certain in utero infections.  The exact biological cause for both optic nerve hypoplasia and micropapilla are not well understood at this time.

Diagnosis of Optic Nerve Hypoplasia and Micropapilla in Dogs

Generally, unless there has been some notice taken of the above symptoms or of situations which bring vision impairment to the forefront of the owner, most of these congenital conditions are found during a routine ophthalmoscopic examination.  Since the optic nerve is the only portion of the central nervous system which can easily be observed, assessing it can help to identify many systemic issues, both in canines as well as in humans.  Your veterinary professional will need to instill special eye drops to obtain pupil dilation so that he can utilize his direct and indirect ophthalmoscopes to look directly at the optic nerve.  These specialized ophthalmic instruments can enable him to get a really detailed look at the inside of the eye, especially the optic nerve.  

Neither of these conditions seems to have an inflammation component so blood work is not likely to be needed unless something vascular is noted during this examination. If a diagnosis of the degree of vision loss of the afflicted dog is required, specialized testing can be done to ascertain some of the vision loss. This testing is not as accurate in canines, who can’t respond to the stimuli as clearly, as it is in most humans, who can respond clearly to the stimuli.

Treatment of Optic Nerve Hypoplasia and Micropapilla in Dogs

Since the cause of optic nerve hypoplasia is a genetic underdevelopment of retinal/neurologic tissue, there is no treatment for it.  There is no inflammatory component generally to optic nerve hypoplasia so there isn’t anything inflammatory to treat either.  In the case of micropapilla, there is no vision loss involved so treatment of the condition isn’t necessary.  

There is also no inflammation involved with micropapilla in dogs, with the optic nerve being the main retinal component which is smaller in diameter than normal.  The optic nerve hypoplasia has been found most frequently in poodle breeds.  If you have a Poodle in your breeding pool who is afflicted with this condition, it would be best not to breed the canine so that the genetic trait isn’t passed on to offspring.

Recovery of Optic Nerve Hypoplasia and Micropapilla in Dogs

In the case of optic nerve hypoplasia, expect that your dog or puppy will suffer vision loss which may be progressive as he ages.  This vision loss should not affect the length of the dog’s life and possibly not even the quality of life, though, understandably, some normal “doggie” activities won’t be possible since the dog’s vision is being compromised and those activities won’t be safe for him to perform.  

In the case of micropapilla in dogs, since there isn’t a vision loss involved, there should be no change in the length, quality and lifestyle activities for the dog, except that you might wish to be cautious in any breeding processes.  While the micropapilla is a genetic anomaly and is considered a normal variation of the optic nerve, it might not be advantageous to pass the DNA along to offspring.