Ultrasonography and Lens Implantation

Dr. P. A. M. Léonard, Lange Leemstraat 128, Antwerpen (Belgium) In order to be able to determine the power of the implant lens pre-operatively, the following data should be available for both eyes: radius of the cornea, depth of anterior eye chamber, length of the axis, refraction. The question arises to what degree these data, all acquired before the operation, may be subject to certain variations as a result of the operation; to find an answer to this question, a number of eyes were treated by one and the same operator (Dr. C. D. Binkhorst) and followed up ad hoc: in 24 eyes the cornea proved to vary as follows: 8 times an increase of 0.3 D; 3 times a decrease of 0.45 D and 13 times no difference. The same comparison was made for the length of the axis in 26 eyes: 12 times no change, 11 times 0.2 mm increase after the operation, and 3 times a decrease of 0.2 mm. The reliability of the data with respect to the end refraction was checked in 31 eyes that could be measured accurately after the operation and in which, according to the manufacturer, the power of the implant was 19.50 D. In 23 cases there was an average difference of 1.2 D (to be interpreted as a greater value attributed to the axis length in relation to the real condition) and in four eyes an average difference of of 0.60 D in opposite sense (shorter axis length measured than real) in another four eyes there was no difference. The possible sources of error are indicated. LEONARD 277 Discussion Binkhorst: We are of course faced with cataractous lenses in which the velocity of the ultrasonic waves can be greater than in other clear lenses. Can colleague Leonard say what is the maximal error expressed in millimeters axis length? Leonard: According to Jansson and others, the velocity in cataractous lenses may vary between 1,540 and 1,660 m/sec; this implies errors of 0.2-0.3 mm. Binkhorst: There are still a few unmentioned problems in the deíermination of the optimal lens power. One of them is the prediction of the postoperative depth of the anterior eye segment. I have never seen any relationship with the preoperaíive depth. A suitable basis may be the distance from the corneal apex to the plane through the iris root. We placed a specially constructed small instrument, provided with a micrometer screw, at the level of the iris basis (visualized by diascleral trans-illumination) and brought it into contact with the corneal apex. So far the instrument has been used too little to evaluate its usefulness. The average of 2.8 mm, formerly found by me in 29 pseudophakous eyes, may be too low in the light of the present technique. Nowadays this average will be rather in the neighborhood of 3.2-3.5 mm. Leonard: For the iris clip lenses there is a difference in anterior eye chamber between determinations in the sitting position, for example with the Jaeger, and in the lying position with