Changes in corneal thickness after daily and extended wear of hydrogel lenses: a comparison of optical and ultrasonic pachometry

Central corneal thickness of both eyes of 18 normal subjects was measured in a study comparing a Haag-Streit optical pachometer and an ultrasonic pachometer (Teknar Ophthasonic, preset velocity 1630 m/sec). All subjects were awake for 3 hours before measurements to reduce swelling of the cornea from overnight eye closure. Reliability was assessed by a three-way analysis of variance between repeated measurements for the optical and ultrasonic pachometers. The former revealed a systematic right–left difference, the left cornea being significantly thicker. The correlation coefficient indicates that the link between the two variables is 0.92 and 0.88 for right and left eyes, respectively. It is concluded that, for clinical purposes, optical and ultrasonic pachometry techniques are comparable. The effect of the daily and extended-wear contact lenses on central corneal thickness also was studied. The degree of change (morning vs evening) in corneal thickness of the polymacon group was lower and decreased with the wear, whereas in the etafilcon A group the change was greater and almost constant with the time of wear.