FEVR (Familial Excudative Vetroretinapathy)
Familial Excudative Vitreoretinopathy also known as FEVR is a genetic condition that is inherited from either parent. It can affect the development of the blood vessels in the eye. There can be any degree of malformed vessels. It can be so minor to where you could have it and never know or severe enough that it causes complete blindness. Up to 40% of people with FEVR never have any symptoms.
It can affect one or both eyes. It can also be minor in one and severe in the other. The blood vessels that support the retina on the edges don't develop properly due to genetic makeup. Depending on how many vessels are effected this can minor retinal issues all the way to retinal detachment. If clinical signs are present this is usually diagnosed during infancy.
Angiogram of normal eye
You can see in the photo the vessels spanning the eye and supplying the eye with blood for proper developement.
Angiogram of eye with FEVR with retinal detachment
You can can see in this eye the vessels aren't as clearly defined and stop abruptly at the edge. The grey shadow being pulled to the left side of the image is the retina becoming detached towards that side due to the lack of blood supply.
Norrie Disease
Norrie causes very similar issues with the eye as it is the same root problem of lack of blood vessel development. Familial excudative vitreoretinopathy is more or less 1 symptom of Norrie disease. Norrie is a genetic condition as well however it inherited from the x chromosome meaning for a boy to have it it comes from the mother (I will get further into genetics in a future post). Unlike FEVR, Norrie always comes with either severe or total vision loss via familial excudative vitreoretinopathy. From what I understand while both eyes may not be exactly the same it does always effect both eyes. With Norrie you are more at risk of being totally blind and having deformed appearance of the eye. Because the deformed or lack of blood vessels supporting the growth of the retina and eye the eyes are more often smaller, closer together, and pupils larger than normal. Sever visual impairment is always a symptom of Norrie however there are many other symptoms that may or may not also be present depending on the individual.
Other Symptoms of Norrie
Hearing loss - Most people with Norrie suffer from progressive hearing loss often in the second decade of life. It can be a gradual loss or sudden with little to no warning. Often it hearing will suddenly go and come back several times before going completely.
Mental delays and Cognitive function - Approximately 30-50% of people with Norrie will have cognitive and developmental delays. Often this looks similar to autism and falls somewhere on that spectrum.
Behavioral Issues - 20-30% of Norrie cases show behavioral issue in particular those associated with aggression. This can be as severe as schizophrenia.
Endocrine abnormalities - More rare yet still occurring in Norrie patients is endocrine abnormalities. This comes into play at the time of puppetry and can result in long term erectile disfunction.
Seizures - Again more rare but still a symptom of Norrie is seizures. These can be mild to severe in frequency and seizure episode itself.
Venous Stasis Ulcers - I am not as educated on this, but this can cause swelling, redness/ rash, and ultimately wounds.
Depending on presence and severity of symptoms patients with Norrie disease may have a shorter life expectancy as well.
Both of these diseases are very rare. Because of tis it is hard to get exact numbers on each. To give you an example of how rare they are there are only approximately 200 known cases of Norrie disease in the world. Because the initial symptoms are almost identical the only way to diagnose is with genetic testing. Stay tuned to learn more about genetic associated with these diseases...