This article is currently a stub to provide some background for the article on nystagmus. I promise to flesh it out more in the future, and would love to answer any questions in the process.
Familial Exudative Vitreo-Retinopathy (FEVR) is a genetic condition affecting the process of blood vessel formation in the retina of the eye. The diagnosis of FEVR covers an incredibly broad spectrum of disease presentation, from eyes that have normal vision to eyes with completely detached retinas (and, obviously, no vision at all). Because the process of blood vessel formation involves a long chain of chemical events and signals, there are quite a few genetic mutations that can lead to FEVR, and they can follow all types of inheritance patterns. Some of these mutations can affect parts of the body beyond the eyes. Our family has the FZD-4 mutation. This mutation follows an autosomal dominant inheritance pattern and only affects the eyes. Because this is the form we deal with, I am not as familiar with the mutations that affect other parts of the body, such as LRP-5.
The differential diagnosis that doctors learn for FEVR is, “Looks like ROP (retinopathy of prematurity), but the infant was full-term.” This differential, combined with Brian’s misdiagnosis, is why FEVR went undiagnosed in our family for so many years. Our triplets were premature, born 14 weeks early at 26 weeks gestation. The girls were diagnosed with ROP. As it turned out, they really had FEVR, but this went undetected because of the differential.
One of the characteristics of FEVR is the presence of exudates, fluids that leak out of the retina in the the liquid vitreous of the eye. The leakage occurs because of the poor quality of the blood vessels in the eye. These exudates are one of the ways that the disease can progressively worsen and even completely steal a patient’s vision. When the exudates collect in between the layers of the retina, they can lead to retinal detachment. Doctors will treat these exudates by cauterizing the leaky area with laser surgery. When the exudates leak into the vitreous, they can stick together, or “organize,” into long strands that pull on different points of the eye, also potentially resulting in retinal detachment. When this happens, it is treated by a surgery called a vitrectomy, where the vitreous gel is completely removed from the eye and replaced by an artificial fluid. This removes the offending exudates, and the body gradually replaces the artificial fluid with new vitreous. Depending on the severity of the leakage, a vitrectomy may be accompanied by a chemical retinal peel, almost like an exfoliation of the surface of the retina, to remove any exudates that may be stuck there.
Another characteristic of FEVR is the abnormal growth of blood vessels. Not only do they form poorly, the eye often grows too many of them. When too many blood vessels grow in a particular part of the retina, they cause that part of the retina to fold and buckle, detaching it from the nerves in the back of the eye and obscuring vision. Sometimes these folds can even bulge up and cover the front of the eye partially or completely. When these folds appear soft and rounded, like hills, they can sometimes be treated through surgery so that they fall back a bit, reattaching to the back of the eye and improving vision. Kender and Jarod both had this surgery done in one eye, peeling retinal tissue from the front of the eye and allowing it to fall back. Caitlin also has a soft fold like this, but it is small and contained within the edge of her eye. When the retinal folds appear sharp and knife-life, however, it means the back of the retinal tissue has stuck to itself inside the fold. These folds cannot be reduced, and must instead be monitored closely to make sure they don’t pull on the rest of the eye and cause further detachments. Kender has a fold like this in his left eye.
When FEVR presents in an advanced stage at birth, the eyes often form with fewer functioning blood vessels, and structures such as the macula and fovea may be malformed or completely absent due to lack of nourishment during development. Because the macula and fovea are the parts of the eye responsible for focal vision, this change in structure alone can dramatically reduce the functional vision of FEVR patients, leaving them with peripheral-quality vision. This would be like only being able to see out of the corners of your eyes, without being able to turn and focus. We believe that this leads to the presentation of nystagmus as a compensating behavior. Because you see better out of your peripheral vision when things move, nystagmus is a way to provide that movement for the entire eye, thus improving functional vision. Both Brian and Kender, who have very poor vascularization of their stage IV retinas, present with nystagmus.
More to come. I could write for hours and hours on this, but family duties call.