Abstract
Torpedo maculopathy (TM) is a rare congenital defect of the retinal pigment epithelium (RPE). The RPE is often evaluated clinically using fundus autofluorescence (AF), a technique that visualizes RPE structure at the tissue level from the intrinsic AF of RPE fluorophores. TM lesions typically emit little or no AF, but this macroscopic assessment is unable to resolve the RPE cells, leaving the organization of the RPE cell mosaic in TM unknown. We used fluorescence adaptive optics scanning laser ophthalmoscopy (AOSLO) to show here for the first time the microscopic cellular-level structural alterations to the RPE cell mosaic in TM that underlie the tissue-level changes seen in conventional clinical imaging. We evaluated two patients with TM using conventional clinical imaging techniques and adaptive optics (AO) infrared autofluorescence (IRAF) in AOSLO. Confocal AOSLO revealed relatively normal cones outside the TM lesion but altered cone appearance within it and along its margins in both patients. We quantified cone topography and RPE cell morphometry from the fovea to the margin of the lesion in case 1 and found cone density to be within the normal range across the locations imaged. However, RPE morphometric analysis revealed disrupted RPE cells outside the margin of the lesion; the mean RPE cell area was greater than two standard deviations above the normative range up to approximately 1.5 mm from the lesion margin. Similar morphometric changes were seen to individual RPE cells in case 2. Multi-modal imaging with AOSLO reveals that RPE cells are abnormal in TM well beyond the margins of the characteristic TM lesion boundary defined with conventional clinical imaging. Since the TM fovea appears to be fully formed, with normal cone packing, it is possible that the congenital RPE defect in TM occurs relatively late in retinal development. This work demonstrates how cellular level imaging of the RPE can provide new insight into RPE pathologies, particularly for rare conditions such as TM.
Highlights
Torpedo maculopathy (TM) is characterized by the presence of a well-circumscribed lesion of the macula featuring elements of hyperpigmentation and atrophy at the level of the retinal pigment epithelium (RPE) and named for its typical shape and orientation with respect to the fovea [1, 2]
Given the well-circumscribed nature of TM, our hypothesis was that the transition from abnormal to normal cellular mosaics would be relatively abrupt, with abnormalities confined to the immediate vicinity of the lesion
Contrary to our expectation that the transition from abnormal to normal cellular mosaics would be relatively abrupt, with abnormalities confined to the immediate vicinity of the lesion, we found that RPE morphometric alterations extended well beyond the bounds of the clinically defined TM lesion
Summary
Torpedo maculopathy (TM) is characterized by the presence of a well-circumscribed lesion of the macula featuring elements of hyperpigmentation and atrophy at the level of the retinal pigment epithelium (RPE) and named for its typical shape and orientation with respect to the fovea [1, 2]. In TM, OCT sometimes reveals neurosensory retinal layers detached from the RPE, forming a cavity [7, 8]. Wong et al classified TM into Types I and II, the latter including neurosensory detachment with subretinal cavitation [9]. Functional testing with visual fields [11] and microperimetry [9] has shown reduced sensitivity in the lesion. Collective responses from electroretinogram (ERG) exams performed on patients with TM have not shown any abnormalities [12]. Multifocal ERG has shown amplitude reduction with potential latency between pathological and healthy retinal areas of the same eye [12, 13]
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