Nanophthalmos: Year of the Zebra 2025

Nanophthalmos is a rare birth condition where one or both eyes don’t grow to their full size during fetal development. Unlike microphthalmos, where there may be other structural anomalies, nanophthalmos refers specifically to the size of the eye, meaning despite being small, all eye structures are intact.

The exact cause of nanophthalmos isn’t fully understood, though it appears to be linked to genetic changes that interfere with eye development. One of the most important measurements here is the axial length, which is the distance from the front to the back of the eye. Axial length plays a major role in how well the eye focuses light onto the retina, which is essential to see clearly. Imagine the retina as the screen in a movie theater, and the lens of the eye as the projector. If the projector is too close or too far from the screen, the image will end up looking blurry or out of focus.

In nanophthalmos, the axial length of the eye is too short, which means light focuses behind the retina instead of on it. This leads to farsightedness, also called hyperopia, where nearby objects look blurry while distant ones may still be clear.

Because the eye is smaller, the anterior chamber, or the space at the front of the eye where fluid normally drains, is shallow and tight. This poor drainage makes it easier for pressure to build up inside the eye, increasing the risk of glaucoma, particularly a type called angle-closure glaucoma. As pressure within the eye rises, it first damages the edges of the optic nerve, leading to loss of peripheral vision. Over time, if not treated, it can also affect central vision and lead to permanent vision loss.

Another possible complication is serous retinal detachment, where fluid builds up between the retinal layers, causing them to peel away from the underlying layer of support tissue. This type of retinal detachment can cause blurry or distorted vision, like straight lines appearing wavy or a dark spot in the visual field.