Pseudoduplication of Fovea in a Human Eye

Duplication of the optic disc and fovea is known to occur in lower vertebrates.^1,2 Although additional optic discs usually serve no purpose, bifoveate birds (eg, swallows) use the additional fovea for limited conjugate binocular movements.² Doubling of the optic disc, true diastasis as well as coloboma, has been described in the human eye.¹ We report the unusual clinical finding of 2 foveae in 1 eye of a patient.

A 25-year-old man had experienced diminished vision in the right eye for several months. There was no history of ocular injury or inflammation. His perinatal and family histories were unremarkable. Best-corrected visual acuity was 20/80, N12 OD and 20/20, N6 OS, with low myopic correction. The anterior segment was unremarkable in each eye. Fundus examination of the right eye revealed macular pucker and peripheral telangiectasia with exudation, suggestive of Coats disease. Fundus examination of the left eye revealed 2 parafoveal halos with 2 foveal reflexes; the temporal reflex was slightly distorted (Figure, A). No other ocular structure exhibited duplication. Optical coherence tomography using a Stratus OCT 3 (Carl Zeiss Meditec, Dublin, California) supported the clinical appearance of foveal duplication: the temporal fovea demonstrated a similar slope of clivus and the recession of inner retinal layers as the central fovea. However, the recession was not complete; a thin layer of inner retinal neurons remained above the photoreceptor layer, the probable cause of blunted foveal reflex. Despite additional layers, the central fovea (thickness, 165 μm) and the accessory fovea (thickness, 160 μm) were similar in thickness, probably owing to less-elongated photoreceptors in the latter (Figure, B). Fundus fluorescein angiography demonstrated only 1 foveal avascular zone, corresponding to the central fovea. A nonspecific mottled hypofluorescence was observed in the area of the temporal fovea (Figure, C). Fundus fluorescein angiography of the right eye revealed leaking telangiectasia and avascular areas in the inferotemporal periphery. Orthoptic evaluation revealed no fixation abnormalities in the left eye; the patient fixed consistently with the central fovea. Automated perimetry using the central 10-2 threshold test protocol (model 720i, Humphrey Field Analyzer II; Carl Zeiss Meditec) showed a normal foveal threshold (31 dB) at the fixation point, with a typical gradient of reducing sensitivity toward the periphery; no anomalous increase in sensitivity was registered temporal to the fixation point (central fovea). The patient was advised, but declined, to undergo pars plana vitrectomy and endophotocoagulation in the right eye.

It has recently been suggested that slow development of central retinal vasculature creates hypoxic stress in the inner retinal neurons, which adapt by thinning out into incipient foveal depressions at approximately the seventh month of gestation.³ Active centrifugal migration of neuronal cells further deepens the depression, and stretching of Muller cells condenses and elongates the foveal cones.⁴ The foveal avascular zone is created 3 to 4 weeks postnatally by the inhibition of centripetal migration of astrocytes, the templates for endothelial proliferation. Foveal maturation is complete by age 3 to 4 years.³ Although we cannot explain this foveal duplication, it is possible that a transient metabolic injury in the perinatal period resulted in an additional zone of hypoxic stress and that consequent focal thinning began to create an immature foveal architecture, aborted before vascular differentiation. Although the extra fovea in this patient was incidentally discovered and nonfunctional, we are unaware of any study documenting its presence in a human eye. The presence of Coats disease in the fellow eye was most likely a chance occurrence, unrelated to the foveal duplication.

Correspondence: Mr Shukla, Aravind Eye Hospital and Postgraduate Institute of Ophthalmology, 1 Anna Nagar, Madurai 625 020, Tamil Nadu, India (daksh66@gmail.com).

Author Contributions: Mr Shukla had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Financial Disclosure: None reported.