OCT Imaging in Patients With Achromatopsia and Blue–Cone–Monochromatism – A Quantitative Approach to OCT Scanning Results

Abstract

Abstract: : Purpose: To show OCT differences in the retina in patients with Blue–Cone–Monochromatism (BCM) and Achromatopsia (ACH) compared to healthy individuals (normals). Methods: Prospective study in patients with BCM and ACH. Fifteen ACH, 6 BCM and 20 normals were examined. Diagnosis of BCM and ACH was established by: vision testing (BCVA Snellen and EDTRS), slit lamp examination, color vision testing (Panel D15 and Berson Test for Rod Monochromatism), Ganzfeld–ERG recording (ISCEV protocol). OCT imaging was done with Zeiss Stratus OCT 3. OCT images were analyzed calculating density profiles from 20 scan–lines through the fovea. Profiles were averaged and analyzed quantitatively for retinal thickness and distances between different retinal reflectivity layers (4 intensity peaks). Results: Normals had mean BCVA of 25/20 and passed all color tests. ACH and BCM had mean BCVA of 20/200 and 20/60 respectively. ACH passed no color test, BCM only Berson’s test. A normal OCT profile contains 4 peaks (P1–P4), presumably representing: RPE (P1), a highly reflective layer delimiting inner and outer rod segments (P2), outer limiting membrane (P3) and inner limiting membrane (P4), (subjective correlation with retinal anatomy). Distinct OCT reflection profiles were established for normals, BCM and ACH. Mean retinal thickness (distance P1 to P4) did not differ significantly between normals and ACH (192±14 vs 187±20µm, always mean ± sd) but both were significantly different from BCM (153±16µm) (p<0.001). ACH and normals show comparable reflection profiles except for P2 (absent in ACH). Distance P1–P3 in normals and ACH did not differ significantly (82±5 vs 78±10µm). P2 is found in BCM but it is clunged to P1 (distance in Normals 48±4, in BCM 32±6µm). P3 is absent in BCM. Conclusions: OCT scanning allows to show distinctive patterns in hereditary retinal diseases. Reflection profiles can be interpreted quantitatively and might be of use in distinguishing retinal diseases affecting the photoreceptors. ACH and normal profiles seem to show similar retinal thickness, whereas BCH show a decreased retinal thickness.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • retinal degenerations: hereditary • photoreceptors