Differences in axial eye length and retinal structure between patients with achromatopsia and blue cone monochromacy

Abstract

Purpose : Achromatopsia (ACHM) and blue cone monochromacy (BCM) share many clinical features – poor visual acuity, light sensitivity, nystagmus and severe color vision defects – often posing a diagnostic challenge. Literature examining clinical differences in these populations is sparse, especially in genetically-characterized patients. Our aim was to assess axial length of the eye and retinal structure in molecularly-confirmed ACHM and BCM patients.

Methods : Our population (aged >16 years) consisted of 164 males with no ocular pathology, 44 with ACHM (9 CNGA3-associated; 35 CNGB3-associated) and 20 with BCM (11 caused by C203R mutations; 9 with a locus control region [LCR] deletion). Axial length was measured in all eyes. Retinal images were acquired using optical coherence tomography (OCT) and used to evaluate, where possible, foveal hypoplasia (retention of one or more inner retinal layers) and the presence of band 2 at the fovea. Analysis was confined to the right eye.

Results : Mean axial length was 24.61 mm in normal eyes (range = 21.54 to 28.68 mm), 24.34 mm in ACHM (range = 19.80 to 29.27 mm), and 26.23 mm in BCM (range = 23.67 to 28.26 mm): ANOVA revealed a significant group effect (p < 0.001). Post-hoc analysis showed significant differences between BCM and both normal and ACHM (p < 0.001). Within BCM, eyes with LCR deletions were longer than those with C203R mutations (p = 0.019, unpaired t-test). OCT results were analyzed using Fisher’s exact test. Foveal hypoplasia was more prevalent in ACHM than BCM (p = 0.001). Although hypoplasia was equally frequent in CNGA3 (n = 9) and CNGB3 (n = 34) ACHM patients (p > 0.999), it was significantly more prevalent in BCM patients with C203R mutations (n = 10) than those with LCR deletions (n = 8, p = 0.036). The frequency with which band 2 was observed at the fovea did not differ between ACHM (n = 44) and BCM (n = 19, p = 0.564).

Conclusions : We present clinical differences between molecularly-confirmed patients with ACHM and BCM patients. In contrast to previous reports,¹ we found no difference in the integrity of band 2 at the fovea between the two conditions. Both axial length and foveal hypoplasia differed between the genetic causes of BCM. These readily-obtainable clinical data may help guide genetic testing and inform differential diagnosis.

¹PMID:16505054

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.