Abstract
Purpose: :
Nanophthalmos is a rare bilateral disorder in which the axial length of the eye is short, typically between 15–20mm, and is often associated with extreme hyperopia, usually greater than +8.00 diopters. There is also microcornea, a shallow anterior chamber, thickened sclera, and a high lens/globe volume ratio. These patients have a predilection to angle closure glaucoma, a congested choroid, uveal effusion, and retinochoroidal folds. Patients rarely have a best corrected visual acuity better than 20/40 at any point in their lives, even with an absence of complicating uveal effusion or glaucoma. The reason for this poor visual acuity has not previously been explained, but it has been postulated that nanophthalmos is not associated with an inherent defect in photoreceptor function. The purpose of this study is to offer an anatomic explanation for poor visual acuity in affected nanophthalmic patients.
Methods: :
This is a retrospective case series of 2 unrelated patients with nanophthalmos. The fluorescein angiograms, optical coherence tomograms, fundus photographs, and clinical examinations of all 4 eyes were studied.
Results: :
A lack of the normal foveal pit was noted on clinical examination. This was also noted as lack of the foveal light reflex on fundus photography in all 4 eyes. Optical coherence tomography had been performed in 3 of the 4 eyes, and all 3 showed flat foveas; i.e., there was no visualization of the foveal pit. Additionally, absence of the foveal avascular zone was noted in all 4 eyes on fluorescein angiography.
Conclusions: :
The abnormal foveal vascular architecture, in the form of an absence of the foveal avascular zone, is previously undescribed in nanophthalmos ("simple or pure microphthalmos"), although it has been noted in posterior microphthalmos. This anomaly likely impacts foveal function, offering a novel explanation for the typically poor best–corrected visual acuity in at least some, if not all, nanophthalmic patients. This finding also supports the conventional belief that the normally avascular central fovea, which includes no retinal blood vessels that could block incoming light from gaining unfettered access to the photoreceptors, is important in obtaining a central visual acuity of 20/20 or better. Additionally, this information should be useful to clinicians in deciding when to perform cataract surgery in nanophthalmic patients, given that the abnormal foveal architecture may limit their visual potential.
Keywords: hyperopia • macula/fovea • anatomy