Diagnose My Retinal Photograph: Myelinated Nerve Fiber Layer

Today's retinal photograph of note shows a fluffy white lesion located in the retina, fanning off near the optic nerve.  Below is a classic appearance.

Normal Retina:

Myelinated Nerve Fiber Layer:

The good news?  This finding is very normal, but can give you quite a start when you see it for the first time! Myelinated nerve fiber layer is a benign finding where the myelin sheath that typically lines and insulates the optic nerve when it exists the eye, persist even inside the eye. Normally, the myelin sheath stops before the nerve enters the eye because myelin (the dense white material you see above the nerve in this photo) will prevent light information from reaching any retinal cells underneath it. Myelin sheathing of the nerve is essential to visual function because it speeds up the transmission of information from the eye to the brain.  But if it exists inside the eye, there may be some (usually very subtle) visual loss since myelin is not clear and therefore any cells stuck behind it won't be able to detect light when it enters the eye.

Studies show that myelinated nerve fiber layer is very rare (less than one percent of the population!). The presence of myelin within they eye would occur during gestation, so this is something that you would be born with and would not change in any way as you go through life. Common differential diagnoses include inflammatory or ischemic changes in the eye, like cotton wool spots or edema, but these changes would be acute conditions and would not exist consistently since childhood.  

What this Means to Me

Because myelin blocks the underlying retinal cells, there can be a possible loss of vision associated. For most people, the changes would be of limited consequence such as an enlarged blind spot on a visual field test (the nerve is naturally a blind spot because there are no retinal photoreceptors in that area).  I would expect the patient above to have an enlarged blindspot due to the close proximity of the myelin to the nerve.  In more severe cases, a larger area of myelin could cause more significant visual disruption and even be associated with strabismus (an eye turn).  

It is unusual but possible to develop myelinated nerve fiber layer changes after birth in cases of ocular tumors or trauma, but this is exceedingly rare and a result of a disruption to the normal ocular tissue.

If you have myelinated nerve fiber layer, your doctor will definitely talk to you about this finding (even though it is normal) because it is permanent inside of your eye.  If you see a new doctor in future it will help them know that this is normal for you and not an acute event (like a cotton wool spot) if there was some question.  If you are a suspect for glaucoma in any way (high pressures, suspicious anatomy, family history) then it would be a good idea to establish a baseline visual field test to map the area of defect associated with your myelinated nerve fiber layer.  Glaucoma causes progressive visual field loss, and it is helpful for your doctor to know what a normal field looks like for you in order to track changes with time.

images in this post are provided by eyedolatry