Abstract
PurposeTo examine outer retinal band changes after flash stimulus and subsequent dark adaptation with ultrahigh-resolution optical coherence tomography (UHR-OCT).MethodsFive dark-adapted left eyes of five normal subjects were imaged with 3-μm axial-resolution UHR-OCT during 30 minutes of dark adaptation following 96%, 54%, 23%, and 0% full-field and 54% half-field rhodopsin bleach. We identified the ellipsoid zone inner segment/outer segment (EZ[IS/OS]), cone interdigitation zone (CIZ), rod interdigitation zone (RIZ), retinal pigment epithelium (RPE), and Bruch's membrane (BM) axial positions and generated two-dimensional thickness maps of the EZ(IS/OS) to the four bands. The average thickness over an area of the thickness map was compared against that of the dark-adapted baselines. The time-dependent thickness changes (photoresponses) were statistically compared against 0% bleach. Dark adaptometry was performed with the same bleaching protocol.ResultsThe EZ(IS/OS)-CIZ photoresponse was significantly different at 96% (P < 0.0001) and 54% (P = 0.006) bleach. At all three bleaching levels, the EZ(IS/OS)-RIZ, -RPE, and -BM responses were significantly different (P < 0.0001). The EZ(IS/OS)-CIZ and EZ(IS/OS)-RIZ time courses were similar to the recovery of rod- and cone-mediated sensitivity, respectively, measured with dark adaptometry. The maximal EZ(IS/OS)-CIZ and EZ(IS/OS)-RIZ response magnitudes doubled from 54% to 96% bleach. Both EZ(IS/OS)-RPE and EZ(IS/OS)-BM responses resembled dampened oscillations that were graded in amplitude and duration with bleaching intensity. Half-field photoresponses were localized to the stimulated retina.ConclusionsWith noninvasive, near-infrared UHR-OCT, we characterized three distinct, spatially localized photoresponses in the outer retinal bands. These photoresponses have potential value as physical correlates of photoreceptor function.
Highlights
To examine outer retinal band changes after flash stimulus and subsequent dark adaptation with ultrahigh-resolution optical coherence tomography (UHR-Optical coherence tomography (OCT))
The ellipsoid zone (EZ)(IS/OS)-cone interdigitation zone (CIZ) photoresponse was significantly different at 96% (P < 0.0001) and 54% (P 1⁄4 0.006) bleach
The EZ(IS/OS)-CIZ and EZ(IS/OS)-rod interdigitation zone (RIZ) time courses were similar to the recovery of rod- and cone-mediated sensitivity, respectively, measured with dark adaptometry
Summary
Five dark-adapted left eyes of five normal subjects were imaged with 3-lm axialresolution UHR-OCT during 30 minutes of dark adaptation following 96%, 54%, 23%, and 0% full-field and 54% half-field rhodopsin bleach. Flash bleaching was performed with a high-power 528-nmwavelength LED (LZ4-00G108; LED Engin, San Jose, CA, USA) diffusely illuminating the retina through a 4F Maxwellian view illuminator.[19] The illuminator was built with two 60-mm focal length condenser lenses to uniformly expose a 408 retinal field. For the half-field exposure, illumination was restricted to the inferior retina by placing a black cardstock semicircle in the focal plane. The LED exposure intensity and duration was controlled by a precision current source (B2902A; Keysight Technologies, Santa Rosa, CA, USA). From measurements of the photopic energy (lux-seconds) of the flash exposure at a known distance and the flash durations, we determined the temporally integrated retinal illuminances of the bleaching stimuli in Troland-seconds (TdÁs)[20]
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