Personal Experience with Cataract Surgery

relatively unlimited. l The importance of adjusting predictions to actual postoperative results has repeatedly been stressed. 2 In addition, the relations between implanted lens power and axial length are considered to be nonlinear.3 Therefore, the low ability of the theoretical formulas to adjust to clinical results and the linearity of the terms used in the empirical formulas limit the accuracy of these formulas. To overcome these limitations, we suggest combining the nonlinear terms of axial length and corneal power used in a theoretical formula with constants derived by statistical analysis of clinical results. According to the suggested method, axial length and corneal power measurements of patients with cataract are placed in one of the theoretical formulas. The lens implant power actually required should also be placed in the same formula. This value can be easily calculated using the postoperative refraction and the power of the lens implant used. 4 Then, constants used in the theoretical formula chosen are replaced by new constants, derived from a multivariant regression analysis. To simplify calculations, a constant anterior chamber depth may be assumed. This method provides a new group of formulas which combines both theoretical and empirical approaches. A formula obtained by this method may be regarded as an empirical modification of the theoretical formulas or as an empirical formula that uses the nonlinear terms of the theoretical formulas. The formula obtained is, as any other empirical formula, subject to constant modification, aiming at eliminating any consistent errors. By expanding their formerly limited ability to be modified, an improvement of the theoretical formulas is to be expected. In addition, the use of the nonlinear terms of axial length and corneal power, derived from the optical eye model, in statistical formulas may improve empirical formulas as well. R. Rasooly, M.D. London, England

S. Merin, M. D. D. BenEzra, M.D., Ph.D.

Jerusalem, Israel

REFERENCES 1. Hoffer KJ: Preoperative cataract evaluation: Intraocular lens power calculation. Int Ophthalmol elin 22(2):37-75, 1982 2. Halliday BL: Calculation of intraocular lens power-results in practice. Trans Ophthalmol Soc UK 105:435-440, 1986 3. Sanders D, RetzlaffJ, KraffM, Kratz R, et al: Comparison of the accuracy of the Binkhorst, Colenbrander, and SRK T " implant power prediction formulas. Am Intra-Ocular Implant Soc J 7:337-340, 1981

J CATARACT REFRACT

4. Retzlaff J: Posterior chamber implant power calculation: Regression formulas. Am Intra-Ocular Implant Soc J 6:268-270, 1980

PERSONAL EXPERIENCE WITH CATARACT SURGERY To the Editor: I am 81 years old and the last of my bilateral cataracts was removed about 16 months ago. The first cataract was removed about nine months prior to the last one. With a reasonable amount oflight, I am able to read the newspaper without spectacles using only the implants. Generally speaking, I feel that the operations turned out very well. I was employed by RCA for 34 years and my work was on theater sound and projection equipment as well as large screen TV and the installation and maintenance of electron microscopes. Electron microscopes use very small pinholes and I found out that they were very good instruments (the pinholes) for acquainting one with the inside of the eye. I was able to keep tabs on the growth of the cataract in my left eye for about a year before an operation and implantation of a lens. Using the same pinhole method, I was able to see the birth of my second cataract and followed it to maturity. I developed another method for viewing the cataract about four months before that operation. I estimate that the new method (patent pending) gave about a ten times improvement of the details. A few days after my last operation, I noticed a broad horizontal band of light. The device I used showed a narrow dark line near the center of the lens. I brought this matter to the attention of my ophthalmologist and was told that there was a fold in the capsule. I followed that fold with the use of my new device and after several months the fold worked out of the scene. I have had six bone fractures and in every case the doctor has invited me to see all X-rays connected with the injuries. Why doesn't the ophthalmologist let patients see for themselves the extent of the cataracts? Why is it general practice for the ophthalmologists to project the Snellen chart on the worst possible type of viewing screen? For uniform illumination a specular screen should not be used - a white matte type is much better. I have been a member of the Society of Motion Picture and Television Engineers for more than 50 years. Almost any good text on optics will confirm my opinion of a specular screen. M.W. Gieskieng

Denver, Colorado

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