Microperimetry Features of Geographic Atrophy Identified With En Face Optical Coherence Tomography

Abstract

IMPORTANCE Progressive geographic atrophy (GA) of the retinal pigment epithelium leads to loss of central vision. To identify GA in age-related macular degeneration and assess treatment, correlation of function observed on microperimetry with structure observed on optical coherence tomographic (OCT) images may be of value.OBJECTIVE To characterize the microperimetric function of GA as identified from en face OCT imaging. DESIGN, SETTING, AND PARTICIPANTSIn a case-series study, 20 patients (22 eyes) entered the study at the University of Padova according to preplanned conditions. From March 1 to July 30, 2014, en face OCT images were obtained at the outer retinal layer and choroidal layer levels. The microperimetry sensitivity map was superimposed on the en face OCT images, which had been used to measure GA areas. Relative and dense scotoma rates were calculated in the GA areas. After data collection, the study eyes were divided into 3 groups according to the macular residual mean sensitivity. MAIN OUTCOMES AND MEASURESRetinal sensitivity measured by microperimetry within areas of GA identified by en face OCT images. RESULTS Twenty patients (5 men and 15 women) were included in the study, with a mean (SD) age of 79.5 (7.0) years (range, 69-98 years). Macular residual mean retinal sensitivity was less than 5 dB in 7 eyes (group 1), 5 to 10 dB in 9 eyes (group 2), and greater than 10 dB in 6 eyes (group 3). Mean (SD) GA area differed among the groups at the outer retinal (13.13 [5.03] mm 2 [range, 5.75-21.04 mm 2 ] in group 1; 7.80 [3.25] mm 2 [range, 3.31-13.52 mm 2 ] in group 2; and 3.94 [2.35] mm 2 [range, 1.46-7.90 mm 2 ] in group 3; P = .001) and choroidal (11.83 [5.55] mm 2 [range, 4.55-22.14 mm 2 ] in group 1; 7.00 [4.29] mm 2 [range, 0.90-13.83 mm 2 ] in group 2; and 3.27 [2.29] mm 2 [range, 0.91-7.23 mm 2 ] in group 3; P = .007) layer levels. Mean (SD) GA area imaged at the outer retinal layer level was significantly larger than that imaged at the choroidal level in group 3 (difference, 0.67 mm 2 ; 95% CI, 0.31-1.03 mm 2 ; P = .005), but not in groups 1 or 2. Mean (SD) rate of relative scotoma was significantly higher in the GA area imaged at the outer retinal layer level than at the choroidal level in group 3 (47.70% [31.30%] [range, 13.60%-100%] vs 34.00% [37.30%] [range, 0%-100%]; difference, 13.74%; 95% CI, 3.84%-23.63%; P = .02), but not in groups 1 or 2. CONCLUSIONS AND RELEVANCEIn the early stage of GA, when retinal sensitivity is relatively good, these data suggest that the GA area imaged on en face OCT at the outer retinal level correctly detects the wide functional degenerative involvement of the photoreceptors. These findings provide novel data that correlate function and structure, which may be of value when assessing treatments that might prevent or reduce the rate of growth of GA.

Optical Coherence Tomography Features Preceding the Onset of Advanced Age-Related Macular Degeneration

“…19 It has also been identified in clinically preserved macular areas in the topography of quiescent NV 20 or surrounding overt GA lesions. 21,22 Prior evidence of early photoreceptor dysfunction in the course and progression of AMD is in alignment with our anatomic findings.…”

A Revised Hemodynamic Theory of Age-Related Macular Degeneration

“…Taking this concept to its logical conclusion, we hypothesize that local variation in hemodynamic parameters, such as wall shear stress and residence time within the choriocapillaris govern the exquisitely focal nature of AMD pathogenesis, which is a centrally defining, yet unexplained, feature of the disease correlating strongly with retinal function [35]. …”

Microperimetry for geographic atrophy secondary to age-related macular degeneration

“…Mesopic microperimetry assesses visual function under medium-light conditions in which both rod and cone receptors are functional. 8,27,38 Mesopic microperimetry tests are typically administered in a dimly lit room without prior light/dark adaptation 16 or using mydriatics. 8,27,38 Alternatively, scotopic microperimetry is performed under dark-adapted conditions and predominantly measures the function of rod photoreceptor cells in healthy eyes.…”

“…8,27,38 Mesopic microperimetry tests are typically administered in a dimly lit room without prior light/dark adaptation 16 or using mydriatics. 8,27,38 Alternatively, scotopic microperimetry is performed under dark-adapted conditions and predominantly measures the function of rod photoreceptor cells in healthy eyes. 11,39 In diseased eyes in which rods are affected, dark-adapted sensitivity may also be mediated by cone photoreceptor cells.…”

“…The actual area of the retina that is stimulated by each of these beams will vary depending on several parameters, including the ocular axial length and angulation of the stimulus. Spot size 3 (0.43 ; 125-mm diameter on the retina, assuming standard parameters) is equivalent to the Goldmann III test object and has been used in multiple studies 16,24,26,27,38 ; however, for instances when precise sensitivity measurements are required, spot size 3 may stimulate too large of an area of the retina. 16 Spot size 2 (0.22 ; 62.5-mm diameter on the retina, assuming standard parameters) may be used in these circumstances.…”