Evidence of outer retinal changes in glaucoma patients as revealed by ultrahigh-resolution in vivo retinal imaging

Abstract

AIMS; It is well established that glaucoma results in a thinning of the inner retina. To investigate whether the outer retina is also involved, ultrahigh-resolution retinal imaging techniques were utilised.

Methods: Eyes from 10 glaucoma patients (25-78 years old), were imaged using three research-grade instruments: (1) ultrahigh-resolution Fourier-domain optical coherence tomography (UHR-FD-OCT), (2) adaptive optics (AO) UHR-FD-OCT and (3) AO-flood illuminated fundus camera (AO-FC). UHR-FD-OCT and AO-UHR-FD-OCT B-scans were examined for any abnormalities in the retinal layers. On some patients, cone density measurements were made from the AO-FC en face images. Correlations between retinal structure and visual sensitivity were measured by Humphrey visual-field (VF) testing made at the corresponding retinal locations.

Results: All three in vivo imaging modalities revealed evidence of outer retinal changes along with the expected thinning of the inner retina in glaucomatous eyes with VF loss. AO-UHR-FD-OCT images identified the exact location of structural changes within the cone photoreceptor layer with the AO-FC en face images showing dark areas in the cone mosaic at the same retinal locations with reduced visual sensitivity.

Conclusion: Losses in cone density along with expected inner retinal changes were demonstrated in well-characterised glaucoma patients with VF loss.

Figure 1

Ultrahigh-resolution retinal images from the three normal subjects. (A) An 18° field of view ultrahigh-resolution Fourier-domain optical coherence tomography (UHR-FD-OCT) image centred at the fovea (from 58 years-old normal subject): 1, external limiting membrane (ELM); 2, junction between inner and outer segments of cone photoreceptors (inner segment (IS)/outer segment (OS)); 3, Verhoeff's membrane (OS/retinal pigment epithelium (RPE)). Scale bar=200 μm. (B) Adaptive optics (AO) UHR-FD-OCT images taken at three different retinal locations (from a 35-year-old normal subject): 1, ELM; 2, IS/OS; 3, OS/RPE. Scale bar=100 μm. Inner segment length (ISL) and outer segment length (OSL) are shown with white solid lines. (C) AO-flood illuminated fundus camera en face images taken at three different retinal locations (from a 21-year-old normal subject). Scale bar=10 μm.

Figure 2

Ultrahigh-resolution Fourier-domain optical coherence tomography (UHR-FD-OCT) images from four glaucoma patients at various retinal locations; two locations with different visual sensitivity were chosen, one with reduced visual sensitivity and the other with either normal or higher visual sensitivity for comparison. Each white dotted box indicates the location where the adaptive optics UHR-FD-OCT image was acquired. I, inferior retina; N, nasal retina; S, superior retina; T, temporal retina.

Figure 3

Adaptive optics (AO) ultrahigh-resolution Fourier-domain optical coherence tomography (UHR-FD-OCT) and AO-flood illuminated fundus camera (AO-FC) en face images from our 10 glaucoma patients. Retinal locations where AO images were acquired are registered to the visual-field maps by numbers. Cone density was calculated from each AO-FC en face image in relation to histology data at the corresponding retinal location. Scale bar=200 μm for AO-UHR-FD-OCT images and 10 μm for AO-FC en face images. I, inferior retina; LE, left eye; N, nasal retina; RE, right eye; S, superior retina; T, temporal retina.

Figure 3

Adaptive optics (AO) ultrahigh-resolution Fourier-domain optical coherence tomography (UHR-FD-OCT) and AO-flood illuminated fundus camera (AO-FC) en face images from our 10 glaucoma patients. Retinal locations where AO images were acquired are registered to the visual-field maps by numbers. Cone density was calculated from each AO-FC en face image in relation to histology data at the corresponding retinal location. Scale bar=200 μm for AO-UHR-FD-OCT images and 10 μm for AO-FC en face images. I, inferior retina; LE, left eye; N, nasal retina; RE, right eye; S, superior retina; T, temporal retina.

Figure 3

Adaptive optics (AO) ultrahigh-resolution Fourier-domain optical coherence tomography (UHR-FD-OCT) and AO-flood illuminated fundus camera (AO-FC) en face images from our 10 glaucoma patients. Retinal locations where AO images were acquired are registered to the visual-field maps by numbers. Cone density was calculated from each AO-FC en face image in relation to histology data at the corresponding retinal location. Scale bar=200 μm for AO-UHR-FD-OCT images and 10 μm for AO-FC en face images. I, inferior retina; LE, left eye; N, nasal retina; RE, right eye; S, superior retina; T, temporal retina.