Sir,

Complete absence of retinal vasculature is extremely rare; to date there have been four such reports published.1, 2 It has been previously assumed that such an anomaly necessarily involves a complete lack of vision. We present two siblings who, despite having complete retinal vessel absence, have useful vision. To the best of the authors' knowledge, these are the first avascular, seeing retinae to be described.

Case report

Two sisters, aged three and five (AA, SA) of consanguineous parents, presented with poorly controlled congenital glaucoma. AA had a right phthisical eye following previous surgery and uncontrolled glaucoma in the left. She demonstrated a degraded electroretinogram (ERG) in the right eye (Figure 1); no responses were obtained from the phthisical left eye. No consistent visual-evoked potentials (VEP) were recorded, though she had her eyes closed. AA had a right vitreolensectomy with control of glaucoma with combined dorzolamide and timolol, and bimatoprost. SA had uncontrolled glaucoma and dense cataract on the right with moderately controlled glaucoma in the fellow eye. She demonstrated normal ERGs in the right eye but no consistent responses in the left. Flash VEPs were recorded from both eyes (Figure 1). SA underwent combined left trabeculectomy and trabeculotomy with mitomycin C, with subsequent lensectomy. The right eye glaucoma was controlled topically as for AA. Both children had microspherophakia with marked iris hypoplasia and anomalous dentition. Homocysteinuria was excluded biochemically. Clinically SA was able to navigate in familiar surroundings and play with toys close to her face. Under anaesthesia, dilated fundal examination revealed complete absence of retinal vasculature; photographic evidence was only available from SA (Figure 2).

Figure 1
figure 1

SA demonstrated subnormal predominantly rod driven and cone-mediated retinal responses from the right eye. Degraded noisy responses were obtained from the left. Binocular flash VEPs indicate activation of post retinal visual pathways. AA demonstrated degraded mixed rod cone ERGs from the right eye but not the left. Scotopic rod and photopic cone responses were noisy. AA closed her eyes during VEP flash stimulation and no consistent evidence of post-retinal activation was produced.

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Figure 2
figure 2

(a and b) Colour fundus photographs, taken through a 20D lens, showing grossly cupped optic disc with complete absence of retinal vessels (SA).

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Comment

Physiologically avascular retinae are known to occur in the mammalian world in which the entire metabolic demands are met by the choroidal circulation. Although angiographic studies cannot be justified to provide evidence, this is the presumed vascular source in these two children. Retinae entirely dependent on a chorioidal blood supply are known to be thinner than their intrinsically vascular counterparts; this is presumed, in part, to be a function of the limitation of oxygen diffusion from the choroid.3 When older, confocal scanning laser tomography may confirm the thin retinae in these children.