Abstract
PurposeTo compare foveal hypoplasia and the appearance of the ellipsoid zone (EZ) at the fovea in patients with genetically confirmed achromatopsia (ACHM) and blue cone monochromacy (BCM).DesignRetrospective, multicenter observational study.ParticipantsMolecularly confirmed patients with ACHM (n = 89) and BCM (n = 33).MethodsWe analyzed high-resolution spectral-domain OCT (SD-OCT) images of the macula from patients with BCM. Three observers independently graded SD-OCT images for foveal hypoplasia (i.e., retention of ≥1 inner retinal layers at the fovea), and 4 observers judged the integrity of the EZ at the fovea, based on an established grading scheme. These measures were compared with previously published data from the patients with ACHM.Main Outcome MeasuresPresence of foveal hypoplasia and EZ grade.ResultsFoveal hypoplasia was significantly more prevalent in ACHM than in BCM (P < 0.001). In addition, we observed a significant difference in the distribution of EZ grades between ACHM and BCM, with grade II EZ being by far the most common phenotype in BCM (61% of patients). In contrast, patients with ACHM had a relatively equal prevalence of EZ grades I, II, and IV. Grade IV EZ was 2.6 times more prevalent in ACHM compared with BCM, whereas grade V EZ (macular atrophy) was present in 3% of both the ACHM and BCM cohorts.ConclusionsThe higher incidence of foveal hypoplasia in ACHM than BCM supports a role for cone activity in foveal development. Although there are differences in EZ grades between these conditions, the degree of overlap suggests EZ grade is not sufficient for definitive diagnosis, in contrast to previous reports. Analysis of additional OCT features in similar cohorts may reveal differences with greater diagnostic value. Finally, the extent to which foveal hypoplasia or EZ grade is prognostic for therapeutic potential in either group remains to be seen, but motivates further study.
Highlights
To compare foveal hypoplasia and the appearance of the ellipsoid zone (EZ) at the fovea in patients with genetically confirmed achromatopsia (ACHM) and blue cone monochromacy (BCM)
Foveal hypoplasia judgements were identical between eyes for all BCM patients
The EZ grading was identical between eyes for all BCM patients except JC_11033, whose right eye was graded as grade V and left eye as grade III by a single rater (E.J.P.), demonstrating high interocular symmetry in BCM
Summary
Line scans were registered and averaged to reduce speckle noise in the image, as previously described.[25] Images from both eyes for each patient were reviewed by a single rater (E.J.P.), and the eye with better image quality was selected for further analysis. For the patients with ACHM, SD-OCT images from the right eye of patients included in 2 previously reported studies were used for analysis.[22,24]. For the patients with BCM, foveal hypoplasia was assessed in a binary fashion (i.e., presence or absence) independently by 3 raters (E.J.P., C.S.L., M.G.), with the consensus grade being used for all images. For the patients with ACHM, their previously reported foveal hypoplasia status was used in our analysis. For the patients with ACHM, their previously reported EZ grade was used in our analysis. Because the data were found to have a non-normal distribution, nonparametric tests were used to test for statistical significance
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