Investigation of ciliary body inner diameter in Chinese myopic adults using ArcScan Insight® 100.

BACKGROUND

Ciliary body inner diameter (CBID) was recently reported as a new parameter for Implantable Collamer Lens (ICL) sizing. This study aimed to characterize CBID in Chinese myopic adults using the novel ArcScan Insight 100 very high-frequency ultrasound biomicroscope, identify its associated ocular anatomical factors, and assess its influence on Implantable Collamer Lens (ICL) size recommendations.

METHODS

In this cross-sectional study, 107 myopic eyes of 58 Chinese adults were enrolled. Anterior segment parameters, including CBID, were measured using ArcScan Insight 100. Linear mixed-effect models (LMMs) were fitted to identify determinants of CBID while accounting for inter-eye correlation. The relative contributions of independent variables were evaluated using partR2 . ICL sizes calculated via the Reinstein formula (incorporating CBID) were compared with those from the STAAR OCOS formula (based on white-to-white diameter).

RESULTS

The mean CBID was 10.80 ± 0.48 (range 9.76 to 11.97) mm. Multivariate LMM analysis revealed that wider CBID was independently associated with younger age (P = 0.045), lower crystalline lens rise (CLR, P = 0.011), wider sulcus-to-sulcus diameter (STS, P < 0.001), and smaller STS lens rise (STSL, P = 0.017). PartR2 analyses identified STS (partR² = 0.595) as the dominant contributor, explaining 59.5% of CBID variability. ICL sizes recommended by the Reinstein formula differed significantly from OCOS-based sizes (F = 4.672, P = 0.010), with 49% agreement.

CONCLUSIONS

ArcScan Insight 100 allows direct measurement of CBID using a standardized protocol. In Chinese myopic adults, CBID was normally distributed and was mainly associated with STS. The Reinstein formula, which incorporates CBID, resulted in different ICL size recommendations for half of the eyes compared to the traditional WTW-based method. These findings demonstrate that incorporation of CBID can alter preoperative ICL size recommendations, though its direct effect on postoperative vault prediction requires future surgical validation.