Crystalline lens biometry using A-scan ultrasound and the Orbscan device

Purpose: To analyze the lens biometry obtained by Orbscan and A-scan ultrasound in normal eyes. Material and methods: The lens thickness obtained by A-scan ultrasound and the anterior curvature of the crystalline lens obtained by Orbscan were prospectively recorded in 280 normal eyes (including eyes with ametropia) of 140 patients (10-95 years of age). The correlation of lens biometry with the contralateral measure, patient age and sex, subjective refraction, and other ocular biometric parameters (anterior chamber depth, iridcorneal angle, corneal diameter, central pachymetry, pupil, corneal radii of curvature, and posterior segment length) was assessed. Results: The lens anterior curvature showed no significant correlation in particular with the subjective spherical equivalent; however, the quality of this measure was poor: the reproducibility of the lens anterior curvature was low (the average difference between two successive Orbscan measurements was 14.4%). The correlation with the contralateral eye was poor (r(s)=0.55; p<0.001 versus r(s)=0.97; p<0.001 for lens thickness). Lens thickness showed the strongest correlation with the patient's age (r(s)=0.82; p<0.001); it increased by 0.26 mm per decade. Lens thickness correlated with anterior chamber depth (r(s)= -0.72; p<0.001) and iridocorneal angle (r(s)=-0.65; p<0.001). The last two parameters also correlated with age (r(s)=-0.68; p<0.001 and r(s)=-0.62; p<0.001, respectively). Anterior chamber depth and iridocorneal angle decreased by -0.21 mm and -1.7 degrees, respectively, per decade. Conclusion: Lens thickness is mainly influenced by age and correlates with the anterior chamber depth and the iridocorneal angle. The influence of aging on anterior segment biometry essentially consists in an increase in lens volume.