Chinese and Caucasian ocular topography and soft contact lens fit

The aim was to evaluate the effect of ocular topography on soft contact lens fit in Chinese and Caucasians.

This study evaluated 547 subjects from two ethnic groups, Caucasian (n = 250) and Chinese (n = 297), at investigational sites in three locations: Wenzhou, China, Melbourne, Australia and Jacksonville, USA. Subjects underwent measurement of a range of ocular topographic variables using identical equipment and protocols, including: apical corneal radius (CR), corneal shape factor (CSF) in the two principal meridians, horizontal visible iris diameter (HVID), vertical palpebral aperture (PA), upper lid angle (ULA) and inter-canthal angle (ICA). Subjects were fitted with a spherical lens in two base curves (BCs) (1·Day ACUVUE, 8.50, 9.00 mm) and a toric soft lens (Accelerated Stabilization Design).

The steeper base curve (8.50 mm) spherical lenses gave an acceptable overall lens fit with 98 per cent or more of subjects in both groups, while the flatter lens (9.00 mm) was acceptable in a significantly higher proportion of the Chinese compared to Caucasian group (96 versus 82 per cent, p < 0.0001) . The main difference in fit between groups was for centration; there was significantly less decentration with the Chinese group (8.50 BC: 39 versus 72 per cent, p < 0.0001; 9.0 BC: 63 versus. 85 per cent, p = 0.02). The 8.5 mm base curve showed good centration (none or slight decentration) for 97 per cent of Caucasian eyes and 96 per cent of Chinese eyes. With both groups, there were some significant correlations between lens fit and ocular topographic variables, most notable between upper lid angle and toric lens orientation with the Chinese subjects. Regression analysis also showed key predictive values relating to lens fit.

Detailed ocular measurements suggest anatomical differences between Chinese and Caucasian populations that should be considered in soft lens design. The spherical and toric lenses tested in this study fitted a large proportion of both Chinese and Caucasian eyes and are robust to the ocular differences noted.