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Kirsten G Locke, Donald C Hood, David G Birch; Relationships among Spectral Domain Optical Coherence Tomography (SD-OCT) Parameters and Semi-automated Kinetic Perimetry (SKP) Parameters in Subjects with Autosomal Dominant Retinitis Pigmentosa (adRP). Invest. Ophthalmol. Vis. Sci. 2018;59(9):28.
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Because SD-OCT and SKP are potential sources of outcome measures for clinical trials in inherited retinal disease (IRD), we investigated the relationships among the structural and functional parameters derived from these measures.
Vertical SD-OCT line scans and SKP were performed on or close to the same day for patients with adRP (n=20, age: 17-71 yrs) with various degrees of progression. Only eyes where both endpoints of the ellipsoid zone (EZ), external limiting membrane (ELM), and outer nuclear layer (ONL) could be identified on SD-OCT were included. Each scan was captured at an ART (Automatic Real-time Tracking) of 100, using the Spectralis (Heidelberg Engineering, USA), while centered on the fovea. The endpoints of EZ and ELM were identified on both sides of the fovea. The endpoints of the ONL were taken where the band had become a thin unchanging line. The isopters for V4e, III4e and I4e test targets were obtained with SKP (Octopus 900, Haag-Streit), using an angular velocity of 4°/sec. Blind spots were tested at angular velocity of 2°/sec. Isopter diameters were measured in degrees along the vertical meridian.
Stepwise multiple regression with the 3 spot sizes as the dependent variables revealed that the only significant relationship was between OCT ONL diameter and SKP I4e diameter (p=0.0049). Based upon Bland-Altman plots, the average difference between the I4e field and ONL diameters was 1.1° (95% CI: -5.1° – 2.9°). Average ELM diameter was 5° less and EZ diameter was 6.7° less than the average I4e field diameter. The diameter of III4e was 24.7°, 28.6° and 30.2° larger than ONL, ELM and EZ diameters, respectively. For spot size V, the disparities were 41.7°, 45.7°, and 47.3°.
The field diameter for spot size I4e is closely related to the diameter of the ONL. Thus, the I4e field diameter can be used to select subjects with measurable EZ and ONL regions within an OCT scan area. Perhaps surprisingly, even the smallest kinetic target with a diameter of 0.11° is detected outside of the EZ, suggesting that considerable vision is possible with minimal photoreceptor structure visible on SD-OCT images. This apparent mismatch between structure and function becomes even more evident with larger test targets.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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