Vivian S. Vuong

Effect of Uveal Melanocytes on Choroidal Morphology in Rhesus Macaques and Humans on Enhanced-Depth Imaging Optical Coherence Tomography

Purpose To compare cross-sectional choroidal morphology in rhesus macaque and human eyes using enhanced-depth imaging optical coherence tomography (EDI-OCT) and histologic analysis. Methods Enhanced-depth imaging–OCT images from 25 rhesus macaque and 30 human eyes were evaluated for choriocapillaris and choroidal–scleral junction (CSJ) visibility in the central macula based on OCT reflectivity profiles, and compared with age-matched histologic sections. Semiautomated segmentation of the choriocapillaris and CSJ was used to measure choriocapillary and choroidal thickness, respectively. Multivariate regression was performed to determine the association of age, refractive error, and race with choriocapillaris and CSJ visibility. Results Rhesus macaques exhibit a distinct hyporeflective choriocapillaris layer on EDI-OCT, while the CSJ cannot be visualized. In contrast, humans show variable reflectivities of the choriocapillaris, with a distinct CSJ seen in many subjects. Histologic sections demonstrate large, darkly pigmented melanocytes that are densely distributed in the macaque choroid, while melanocytes in humans are smaller, less pigmented, and variably distributed. Optical coherence tomography reflectivity patterns of the choroid appear to correspond to the density, size, and pigmentation of choroidal melanocytes. Mean choriocapillary thickness was similar between the two species (19.3 ± 3.4 vs. 19.8 ± 3.4 μm, P = 0.615), but choroidal thickness may be lower in macaques than in humans (191.2 ± 43.0 vs. 266.8 ± 78.0 μm, P < 0.001). Racial differences in uveal pigmentation also appear to affect the visibility of the choriocapillaris and CSJ on EDI-OCT. Conclusions Pigmented uveal melanocytes affect choroidal morphology on EDI-OCT in rhesus macaque and human eyes. Racial differences in pigmentation may affect choriocapillaris and CSJ visibility, and may influence the accuracy of choroidal thickness measurements.

Refining the definition of the choroidal–scleral interface

Editor, W e read the article by Ram et al. (2016) with great interest. The authors reported a series of cases describing the use of toric intraocular lens (IOL) in children with significant developmental cataract and preexisting corneal astigmatism. They concluded that toric IOL implantation is an effective option for the correction of corneal astigmatism in children and thereby it significantly improves postoperative visual outcome. We congratulate and applaud their primary effort on this topic. The results displayed in the article are interesting and exciting. However, we believe that some concerns do deserve further discussion and more consideration. First, we fear that some important and necessary ophthalmologic examinations may be ignored in the present study, for example examination of corneal topography and thickness. The corneal tomographers, such as Pentacam, can provide the three-dimensional mapping of the cornea and make subtle elevations more pronounced, which is very critical to detect the early or subclinical keratoconus (de Sanctis et al. 2008). We want to enquire whether the authors had ever considered that some of the recruited childrenmay suffer from the early or subclinical keratoconus. As well known, a diagnosis of clinically evident keratoconus is rarely disputed. However, the differential diagnosis of early forms of keratoconus is still a challenge for clinicians (Davidson et al. 2014). Therefore, we strongly recommend that all the patients should undergo a more comprehensive ophthalmologic examination when a larger clinical research is undertaken in future. Second, the authors have only recorded the postoperative keratometric cylinder at one year. We think that the corneal keratometer should be performed at eachpostoperative visit. Then, we can obtain the change in corneal astigmatismwith advance in time. These results also provide useful information whenplanning toric IOL implantation in children. So, what do you think?