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We report two cases with idiopathic parafoveolar telangiectasis (IPT) that showed a deep invasion of perifoveal capillaries within the substance of the fovea, obliterating the foveal avascular zone. All four eyes revealed characteristic findings of IPT, but demonstrated a deep layer of telangiectatic capillaries occupying the expected region of the foveal avascular zone, with retention of relatively good visual acuity. These cases indicate that the control of capillary growth in patients with IPT is defective, but the presence of vessels alone does not cause a marked decrease in visual acuity.
IPT is an acquired retinal disorder consisting of bilateral deep proliferation of telangiectatic perifoveal capillaries through the depth of the parafoveolar macula, and also centripetally to an extent—in that patients with IPT have smaller foveal avascular zones (FAZs) than normal patients.1 We report two patients with IPT who showed a deep invasion of perifoveal capillaries within the central fovea, causing an obliteration of the FAZ.
Case 1: A 49‐year‐old female had experienced gradual vision loss for several years bilaterally without treatment. Her visual acuity was 20/30 right eye and 20/100 left eye. Both eyes revealed telangiectatic capillaries, intraretinal refractile deposits and right‐angle venules in the macula (fig 11).). Fluorescein angiography clearly demonstrated a deep layer of telangiectatic capillaries occupying the entire expected region of the FAZ. Optical coherence tomography (OCT) bilaterally demonstrated blunting of the foveal depression, hyper‐reflectivity within the central fovea and of the outer nuclear layer in the macula consistent with the vascular infiltration, and disruption of the boundary between photoreceptor inner and outer segments.
Case 2: A 59‐year‐old female had a gradual vision loss to 20/50 right eye and 20/40 left eye. Both eyes revealed telangiectatic capillaries, intraretinal refractile deposits and right‐angle venules (fig 22).). A deep layer of telangiectatic capillaries invading into the expected region of the FAZ was highlighted by fluorescein angiography. OCT bilaterally showed hyper‐reflectivity of the outer nuclear layers in the macula and a break of the hyper‐reflective line between photoreceptor inner and outer segments. The right eye had a loss of the foveal depression and a small amount of subfoveal fluid, whereas the left eye had an intraretinal cavitation.
In addition to telangiectatic vessels, our patients had right‐angle venules, greyish‐white opacification of the macula, and inner retinal crystalline deposits, all of which are typical for IPT. Because of these findings, the likelihood of the vascular findings being congenital is unlikely. Congenital macrovessels2 have been reported with increased vascularity in the foveal region; however, macrovessels are usually solitary, unilateral, and are not associated with retinal opacification or inner retinal crystalline deposits. During embryological development, a superficial layer of capillaries forms in association with astrocytes around the future site of the foveal depression.3 These vessels are excluded from the central foveal region during development.4 Later, a deeper layer of capillaries forms, apparently secondary to vascular endothelial growth factor release by Muller cells.3,5 After the vessels form, the astrocytes retreat from around the fovea.4 For vessels to invade the central fovea later in life, some stimuli for their growth must be present. There are two principle cell types in the central fovea: photoreceptors and Muller cells. As Muller cells are responsible for directing the deeper layer of capillaries during embryology and our patients had a deep proliferation of capillaries into a region that is ordinarily occupied only by photoreceptors and Muller cells, there seems a possibility that the abnormal vessel growth was directed by Muller cells.
Abnormalities involving Muller cells have been implicated in macular structural abnormalities seen in IPT,6 including foveal cavitation, which occurred in one eye of the current cases. We6 suggested that such cavitation is probably attributed to the alteration at the site of a specialized Muller cell found in the inner portion of the fovea centralis—namely, the Muller cell cone.7 Recent reports have also demonstrated a gap at the level of the boundary of photoreceptor inner and outer segments as a characteristic OCT finding in IPT.8,9 Interestingly, experimental disruption of Muller cell metabolism induces photoreceptor dysmorphogenesis.10 Although speculative, Muller cell abnormalities may secondarily affect photoreceptors in eyes with IPT, leading to the deep capillary proliferation.
Competing interests: The authors have no proprietary interest in any aspect of this study.