High Hyperopia after Radial Keratotomy

High Hyperopia after Radial Keratotomy

Table 2. Eye measurements of patients who may be affected by the SRK(f cusp. Axial Length (mm) Corneal Curvature (D) Short eye 24 K> 52.5 K> 49.5 K...

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Table 2. Eye measurements of patients who may be affected by the SRK(f cusp. Axial Length (mm)

Corneal Curvature (D)

Short eye <22 Average eye 22-24 Long eye >24

K> 52.5 K> 49.5 K> 48.3

send or fax a brief report of the K-readings, axial lengths, and preoperative refraction in both eyes to John Retzlaff, M.D., 2900 Barnett Rd., Medford, OR 97504; facsimile (503) 773-8666. If you would like power calculation advice on the patient, we will call you. If the patient has had IOL surgery, include the IOL style and A-constant or ACD constant and the postoperative refraction in the report so we can add the case to our database.

REFERENCES I. Retzlaff J, Sanders DR, Kraff Me. Development of the SRKjT intraocular lens implant power calculation formula. J Cataract Refract Surg 1990; 16:333-340 2. Binkhorst RA. Intraocular Lens Power Calculation Manual-A Guide to the Author's TI-58/59 IOL Power Module, 2nd ed. New York, Binkhorst M.D., P.e., 1981 3. Holladay JT, Praeger TC, Chandler TY, Musgrove KH. A three-part system for refining intraocular lens power calculations. J Cataract Refract Surg 1988; 14:17-24 4. Fyodorov SN, Kolonko AU. Estimation of optical power of the intraocular lens. Vestn Oftalmol 1967; 4:27 5. Olsen T. Theoretical approach to intraocular lens calculation using Gaussian optics. J Cataract Refract Surg 1987; 13:141-145 6. Retzlaff JA, Sanders DR, Kraff Me. Lens Power Calculation-A Manual for Ophthalmologists and Biometrists, 3rd ed. Thorofare, NJ, Slack, Inc, 1990

Antibacterial Concentrations

60 ~g/cc. Solutions used in corneal transplantation, which contained 1,000 ~g/cc of vancomycin were found to be safe. While gentamicin is highly retinotoxic, and concentrations of 4 to 8 ~gjcc might constitute a suitable compromise for prophylactic purposes in pars plana vitrectomy, the corneal endothelium tolerates concentrations of this drug in excess of I00 ~g/cc. I see no reason to use potentially ineffective dosages of antibiotics, provided effective concentrations are safe. The recommendations given by Drs. Kansas, Willerscheidt, and Gimbel may be misprints; 1 if they are not, the mentioned concentrations of 0.5 ~g/cc for gentamicin and 0.5 ~g/cc for vancomycin in the irrigating fluid must be regarded as homeopathic or placebo treatment. From my own experience of more than 20 years of using antibiotics in irrigating solutions, I would suggest concentrations of 20 to 40 ~g/cc of gentamicin (10 to 20 mg/500 ml balanced salt solution) and 50 ~g/cc of vancomycin (25 mg/500 ml balanced salt solution) for anterior segment procedures with an intact posterior capsule. 2 If a substantial anterior vitrectomy has to be performed, this irrigating fluid might be replaced by one that contains lower concentrations of these antibiotics. A further comment to Dr. Gills' suggestions: no amount of "added use of steroids and nonsteroidals" will prevent a bacterial endophthalmitis. Klaus D. Teichmann, M.D. Riyadh, Saudi Arabia

REFERENCES I. Masket S, ed. Consultation section. J Cataract Refract Surg 1993; 19: 108-111 2. Fechner PU, Teichmann KD. Medikamentose Augentherapie, ed 3 (English: Medical Eye Therapy). Stuttgart, Enke, 1991; 345

High Hyperopia after Radial Keratotomy

To the Editor: To the Editor: I read with interest the article by Yehuda Waisberg, In the consultation section regarding antibacterial prophylaxis in cataract surgery,1 several surgeons rec- M.D., Ph.D., "Bilateral High Hyperopia After Radial ommended concentrations of antibiotics in the irrigat- Keratotomy" (J Cataract Refract Surg 1992; 19:88-89), ing solutions that I consider too low. Unfortunately, on a procedure performed in 1981. I was somewhat antibiotics do not sterilize solutions instantaneously; disappointed that a thorough description of the proceeven at bactericidal concentrations they require hours to dure was not given. For example, how small was the kill susceptible bacteria. Some of the concentrations optical zone, were there perforations, and so forth. Also, mentioned may be suitable for inhibiting bacterial at that time many physicians, including myself, periodgrowth, but they are not bactericidal. As there is suffi- ically attempted to cut to Descemet's. Some radial kercient turnover of aqueous humor to dilute the antibiotics atotomy (RK) courses would describe the difference in to less than half their original levels within a few hours, appearance between Descemet's and stroma. We were these should be high enough to guarantee bactericidal also doing multiple stepped incisions and sometimes concentrations for several hours. cutting between the steps. Dr. Gills uses 8 ~g/cc of gentamicin and 10 ~gjcc of I agree with Dr. Waisberg's comment that overcorvancomycin. Bactericidal levels for vancomycin in se- rections are common after RK, but only to a point. rum have been determined to vary between 20 and Articles published early in the 1980s showed overcor446


rection rates between 10% and 15%, and I feel this is consistent with my own early performance. Since 1986, we have run three separate in-house studies of approximately 125 patients and found overcorrection rates of 1% to 2%, and none of these were over 3 diopters (D). I think this has occurred because our perforation rate is extremely low, in the 1% to 2% range. Also, since 1986 I have stopped being so aggressive in trying to cut to 99% depth, and we have strongly instructed patients not to rub their eyes for many years after their RK. Most recently, we came across a patient who had had bilateral RK in 1986. She presented in 1991 with 4.5 0 of hyperopia in her right eye and 1.00 in the left. It turns out that she, since childhood, had slept on her stomach and the right side of her face (right eye). Subsequently, Dr. Canrobert Oliveira ofBrazilia, Brazil, has identified at least ten patients, and Dr. David Davis of Hayward, California, has three, who have this type of unilateral progression and who sleep on their stomach and, therefore, on one eye primarily. In conclusion, at this point in time I think overcorrections are very uncommon, both short- and long-term after RK, if one avoids perforation, goes for an 85% to 95% depth of cut, and strongly advises patients not to chronically rub/knuckle their eyes and to avoid sleeping on their stomach with their face into the pillow or laying on one of their arms. I instruct patients who just have to give their eye a good rub to place their index finger at the outer canthus on bone and simply massage and stretch the lids back and forth with a circular motion over the bone. That feels almost as good. Maurice E. John, M.D. Jeffersonville, Indiana

Yehuda Waisberg, M.D., replies: I appreciate your interest in my recent article on bilateral high hyperopia after RK. As you can find in this case report, RKs were performed in 1986 and not in 1981 as you stated. The surgeries were not performed by myself; although I am a cataract surgeon I do not perform refractive surgery. Both eyes of the patient were operated on by a refractive surgeon in the city in which I live but I do not have precise descriptions of the procedures. My article includes the description of the biomicroscopy of the operated eyes: "eight radial and four transverse keratotomy scars in both corneas with some epithelial cysts in the scars and a central free area between 3 mm and 4 mm." There are no signs of gross perforations; applanation of the central cornea in both eyes can be easily seen in the slitlamp. You present your personal rates of overcorrections after RK. In fact, it was not my purpose to present statistics or discuss this subject but just to report what I consider an unusual and severe complication ofRK that occurred in my patient.

I read with interest your comments on the possible role of eye rubbing and sleeping position on RK results and I would appreciate seeing published results of a well-planned research on this subject.

Effect of Contact Between Lens and Capsule To the Editor: With disappointment I read the article on the consequences of YAG-Iaser capsulotomy in pseudophakic eyes. Like so many others, it fails to address the one clinically important question in this context: Is capsulotomy less dangerous on a capsule that is in tight contact with the posterior surface of the intraocular lens (lOL) than if the capsule is only in loose or no contact with the IOL? I have described,2 and since 1986 have been using, a lens that protrudes comparatively far into the vitreous and keeps the capsule on stretch. I assume that YAG capsulotomy in eyes with a super-reversed lens type causes little if any disturbance in the eye since (1) little energy is required because the capsule is near the nodal point of the eye, wherefore a small opening is clinically sufficient, and (2) the capsulotomy causes an optical opening only, while the barrier between the anterior and posterior segments of the eye is maintained. This bars debris from reaching the anterior chamber angle and aqueous from reaching the retina, thereby preventing postoperative glaucoma and cystoid macular edema. My clinical impression is that the assumption just enunciated is correct. But it is unproven by statistical means. I would have expected the authors to at least have mentioned the type of IOLs (convex-plano or planoconvex) that were implanted in the eyes of the patients in their study. P.U. Fechner, M.D. Hannover, Germany REFERENCES 1. Altamirano D, Mermoud A, Pittet N, et al. Aqueous hu-

mor analysis after Nd:YAG laser capsu!otomy with the laser flare-cell meter. J Cataract Refract Surg 1992; 18: 554-558 2. Fechner PU, Trier HG. Super-reversed intraocular lens. J Cataract Refract Surg 1990; 16:471-476

Carl P. Herbort, M.D., replies: I would like to congratulate Dr. Fechner on his very interesting work in lens design and hope that his assumptions will be verified in the future and will not remain unproven by statistical means.