Anterior chamber depth measured by two methods in myopic and hyperopic phakic IOL implant

To evaluate the accuracy and reliability of the optical versus ultrasonic measurement of anterior chamber depth (ACD) in a group of patients affected by high myopia or hyperopia, before phakic IOL implant.

18 consecutive patients (34 eyes) were enrolled in this study, and asked to undergo phakic IOL implant to correct high myopia or hyperopia. The mean age was 29.5 (SD 3.4) years, the male/female ratio was 10/8. 13 patients (24 eyes) were myopic (mean myopia -16.17 (4.39) D, range -9 to -24 D), whereas five patients (10 eyes) were hyperopic (mean hyperopia 7.4 (2.01) D, range 5.5-11 D). For each patient, ACD was evaluated comparing an optical system (Orbscan topograph system) with a standard A-scan ultrasound system. To evaluate the reliability of the two methods, the average of three optical and 10 ultrasonic consecutive measurements were considered. Statistical analysis was performed by means linear regression.

The average difference between optical and ultrasound values was 0.17 (0.1) mm (4.68% (2.52%)). There was a constant underestimation of the ACD with the optical system compared with the ultrasound measurement, more evident in the hyperopic eyes (5.20% (1. 95%)) than in myopic ones (4.46% (2.72%)). The reliability of measurements, as showed by the standard deviation values, was higher in the optical system (0.03 (0.02)) than in the ultrasound (0.1 (0. 05)), with a statistical difference (p<0.001). The linear regression analysis between optical and ultrasound measurements was 0.8992 (p<0. 0001).

The optical measurement of ACD is an accurate and reliable technique in high myopic and hyperopic eyes. It gives a small underestimation of the ACD values, but it could be preferable to the ultrasound technique, because it demonstrates more repeatability and has the advantages of a non-contact technique.