- Email: [email protected]
Experience with Hexagonal Keratotomy
2. Holladay JT: Evaluating the intraocular lens optic. Surv Ophthalmol 30:385-390, 1986 3. Sellman TR, Lindstrom RL: Effect of a plano-convex posterior chamber lens on capsular opacification from Elschnig pearl formation. ] Cataract Refract Surg 14:68-72, 1988 4. Sterling S, Wood TO: Effect of intraocular lens convexity on posterior capsule opacification. ] Cataract Refract Surg 12:655-657, 1988 5. Lindstrom RL, Harris WS: Management of the posterior capsule following posterior chamber lens implantation. Am Intra-Ocular Implant Soc] 6:255-258, 1980 6. Harris WS: An approach to intraocular lens implantation. In: Rosen ES, Jaining WM, Arnott EJ, eds, Intraocular Lens Implantation. St Louis, CV Mosby Co, 1984, pp 376-382 7. Drews RC: The Pearce tripod posterior chamber intraocular lens: An independent analysis of Pearce's results. Am IntraOcular Implant Soc J 6:259-262, 1980 8. Shah GR, Gills JP, Durham DG, Ausmus WH: Three thousand YAG lasers in posterior capsulotomies: An analysis of complications and comparison to polishing and surgical discission. Ophthalmic Surg 178:473-477, 1986
THE 9 DIOPTER SURPRISE REVISITED To the Editor: In a recent issue of the Journal, Drs. James J. Salz and August L. Reader III published a paper on implant exchanges for incorrect power (Lens implant exchanges for incorrect power: Results of an informal survey. ] Cataract Refract Surg 14:221-224, 1988). The authors describe some very unusual cases and I am sure there are similar cases in many practices that are never reported. The large errors encountered resemble the "9 diopter surprise" described in the early 1970s when implant surgery first became popular in the United States. For those of us old enough to remember, a clinical method was used to calculate the intraocular lens power and the axial length was not routinely measured prior to surgery. It is interesting to note that the incorrect power in most cases reported in the survey are due to gross errors in the original axial length measurement. Large errors in axial length measurement occur when the technician has problems identifying the normal ultrasound pattern, such as in an uncooperative patient or in the presence of intraocular pathology. The problem becomes more complicated. in the very long and very short eye in which the retinal echospike does not rise as high as in the average eye. There is no fool-proof method to avoid an error in axial length measurement, but I would like to share a protocol followed in our office that has proven to be very effective: 1. Bilateral axial length measurements are performed by a certified technician. Each eye is measured three times and Polaroid pictures are taken. Consistency is very important; for the past 12 years we have used the same ultrasound unit, the same 580
J CATARACT REFRACT
technicians, and the same immersion technique. Variations in the ultrasound probe design, in the sound velocity, or in the technique can cause up to 0.5 mm difference in the measurement. 2. One week prior to surgery, I personally review the Polaroid pictures of the measurements. If they are not satisfactory, the patient is recalled and the eye is remeasured. When needed, a B-scan examination will rule out intraocular pathology. 3. The ultrasound results are then correlated with the clinical data and a choice of an implant is made. In most cases, both eyes are within 0.5 mm of each other and the ultrasound results correlate with the clinical data: hypermetropes usually measure less than 23 mm, emmetropes between 23 mm and 24 mm, and true myopes over 24 mm. However, discrepancies will be encountered in some cases. The surgeon should then use his or her clinical judgment in analyzing the data, because it is ultimately his or her responsibility. If the surgeon is not satisfied with the calculations or suspects a possible error, he or she should have the measurements repeated either under his or her supervision or by an outside consultant. It is then, and only then, that a potential 9 diopter surprise can be avoided. H. John Shammas, M.D.
Lynwood, California
EXPERIENCE WITH HEXAGONAL KERATOTOMY To the Editor: I would like to add my clinical experience to the research data reported by my colleagues Drs. Albert C. Neumann and George R. McCarty (Hexagonal keratotomy for correction of low hyperopia: Preliminary results of a prospective study. ] Cataract Refract Surg 14:265-269, 1988). I have performed hexagonal keratotomy on 138 patients (194 eyes) since May 5, 1987. Results on the first 50 eyes of patients 1 through 29 have indicated significant visual acuity improvement in 100% of the cases (Table 1). As presented at the Symposium on Cataract, IOL and Refractive Surgery in Los Angeles in March 1988, the findings on these patients were as follows: Preoperatively • Mean spherical refraction was + 2.97 diopters (D). • Average cylinder was 0.64 D. • Average spherical equivalent was + 2.65 D. • Average K-readings were 43.28 D. • Visual acuity without correction was 20/100. Five eyes were 20/400 or worse. Postoperatively • Average refractive change was 2.80 D. The refractive change increased and appeared to be at approximately its final result about six months after sur-
SURG-VOL 14, SEPTEMBER 1988
Table 1. Results in 50 eyes one month or more postoperatively with cycloplegic refraction. Optical Zone
Number of Eyes
Average Diopter Change
6.00
2
1.00
5.75
3
1.83
5.50
7
2.00
5.25
4
2.93
5.00
34
2.65
gery; the results would be somewhat greater after six months. • Average sphere was + 0.30 D. • Average cylinder was 0.90 D. • Average keratometry increased by 2.49 D. In addition: • Endothelial cell loss averaged 0.3%. • Induced astigmatism was greater than 1 D for four patients. To date, in our first 100 cases we have not had any microperforations, which may account for the low level of astigmatism postoperatively in these patients. Additionally, in tracking these patients, there has been no significant change in the endothelial cell count and there have been no complications to report. In our experience, side effects have been quite similar to those with radial keratotomy. In a few cases, we have patched longer than the first day because of some temporary corneal edema. And we caution the patients to protect their eyes from severe trauma even more so than in radial keratotomy, primarily because, unlike radial keratotomy, the hexagonal keratotomy incisions intersect and touch, weakening the unhealed eye. Finally, because of the intersecting incisions, hexagonal keratotomy requires exceptional surgical accuracy and skill. Extreme care must be taken to make incisions of proper depth. Thus, based on this wider study of 50 eyes (plus another 144 hexagonal keratotomy surgeries performed since then), our findings indicate that the results of hexagonal keratotomy surgery to date demonstrate the excellent promise of this procedure for hyperopic and presbyopic patients. Ronald P. Jensen, M.D.
Glendale, California
UNNECESSARY ALARM ABOUT LOVASTATIN AND CATARACTS To the Editor: The drug lovastatin is being marketed by Merck Sharp & Dohme under the trade name Mevacor®. This J CATARACT REFRACT
medication is a potent agent to lower serum levels of cholesterol; it works by inhibiting an enzyme that catalyzes an early rate-limiting step in cholesterol synthesis. Although some cataracts were produced in dogs given at least 50 times the maximum human dose for prolonged periods,l results in humans have been equivocal. Lovastatin appears to be only a weakly cataractogenic agent, if it is one at all, and only after years of administration. 2 A more recent report suggests that in fact lovastatinhas no adverse effects at all on the human lens. 3 Nevertheless, the manufacturers recommend initial and periodic ophthalmological examinations of patients taking this drug to check for cataract development. Material has appeared in the ophthalmological literature supporting this recommendation. 4 I question whether these exhortations really are in the patients' best interest. Patients taking lovastatin all have dangerously high levels of serum cholesterol. Such levels, it is now accepted, carry an unquestioned increased risk of cardiac and cardiovascular morbidity and mortality. Indeed, many of the patients I see have already suffered one or more myocardial infarctions, and a significant percentage have had coronary artery bypass surgery. These patients, when started on lovastatin, express concern about the apparent risk to their eyes and vision that perhaps is associated with the drug. I wonder if it is really necessary to frighten these patients in this way and to make them undergo the expense of periodic screening for cataracts that may be related only mildly to the use of this drug. Consider the extremely low morbidity and excellent recovery from modern cataract surgery and intraocular lens implantation. Contrast this with the life-threatening dangers of continued high cholesterol levels, usually in a subset of patients who already have had significant cardiac and! or cardiovascular morbidity. In these patients, I cannot conceive of any lens changes that would justify any reduction or elimination of this drug. Any patient who needs this drug should take it without concern for his or her visual future, grateful that he or she lives in an era in which such a medication is available. However, the prescribing physician must react to the package insert, and, in the medicolegal climate in which we live, badger the 20/20 patient into obtaining initial and periodic ophthalmological examinations. What is the point of such examinations? Any patient taking lovastatin (or any patient not taking lovastatin, for that matter) who has decreased vision should be encouraged to consult an ophthalmologist. Otherwise, patients ill enough to require lovastatin should not be forced to worry about "blindness" and the evils of cataracts. Let us hope that the federal authorities come to appreciate that the realities of modern cataract
SURG-VOL 14, SEPTEMBER 1988
.581
THE 9 DIOPTER SURPRISE REVISITED To the Editor: In a recent issue of the Journal, Drs. James J. Salz and August L. Reader III published a paper on implant exchanges for incorrect power (Lens implant exchanges for incorrect power: Results of an informal survey. ] Cataract Refract Surg 14:221-224, 1988). The authors describe some very unusual cases and I am sure there are similar cases in many practices that are never reported. The large errors encountered resemble the "9 diopter surprise" described in the early 1970s when implant surgery first became popular in the United States. For those of us old enough to remember, a clinical method was used to calculate the intraocular lens power and the axial length was not routinely measured prior to surgery. It is interesting to note that the incorrect power in most cases reported in the survey are due to gross errors in the original axial length measurement. Large errors in axial length measurement occur when the technician has problems identifying the normal ultrasound pattern, such as in an uncooperative patient or in the presence of intraocular pathology. The problem becomes more complicated. in the very long and very short eye in which the retinal echospike does not rise as high as in the average eye. There is no fool-proof method to avoid an error in axial length measurement, but I would like to share a protocol followed in our office that has proven to be very effective: 1. Bilateral axial length measurements are performed by a certified technician. Each eye is measured three times and Polaroid pictures are taken. Consistency is very important; for the past 12 years we have used the same ultrasound unit, the same 580
J CATARACT REFRACT
technicians, and the same immersion technique. Variations in the ultrasound probe design, in the sound velocity, or in the technique can cause up to 0.5 mm difference in the measurement. 2. One week prior to surgery, I personally review the Polaroid pictures of the measurements. If they are not satisfactory, the patient is recalled and the eye is remeasured. When needed, a B-scan examination will rule out intraocular pathology. 3. The ultrasound results are then correlated with the clinical data and a choice of an implant is made. In most cases, both eyes are within 0.5 mm of each other and the ultrasound results correlate with the clinical data: hypermetropes usually measure less than 23 mm, emmetropes between 23 mm and 24 mm, and true myopes over 24 mm. However, discrepancies will be encountered in some cases. The surgeon should then use his or her clinical judgment in analyzing the data, because it is ultimately his or her responsibility. If the surgeon is not satisfied with the calculations or suspects a possible error, he or she should have the measurements repeated either under his or her supervision or by an outside consultant. It is then, and only then, that a potential 9 diopter surprise can be avoided. H. John Shammas, M.D.
Lynwood, California
EXPERIENCE WITH HEXAGONAL KERATOTOMY To the Editor: I would like to add my clinical experience to the research data reported by my colleagues Drs. Albert C. Neumann and George R. McCarty (Hexagonal keratotomy for correction of low hyperopia: Preliminary results of a prospective study. ] Cataract Refract Surg 14:265-269, 1988). I have performed hexagonal keratotomy on 138 patients (194 eyes) since May 5, 1987. Results on the first 50 eyes of patients 1 through 29 have indicated significant visual acuity improvement in 100% of the cases (Table 1). As presented at the Symposium on Cataract, IOL and Refractive Surgery in Los Angeles in March 1988, the findings on these patients were as follows: Preoperatively • Mean spherical refraction was + 2.97 diopters (D). • Average cylinder was 0.64 D. • Average spherical equivalent was + 2.65 D. • Average K-readings were 43.28 D. • Visual acuity without correction was 20/100. Five eyes were 20/400 or worse. Postoperatively • Average refractive change was 2.80 D. The refractive change increased and appeared to be at approximately its final result about six months after sur-
SURG-VOL 14, SEPTEMBER 1988
Table 1. Results in 50 eyes one month or more postoperatively with cycloplegic refraction. Optical Zone
Number of Eyes
Average Diopter Change
6.00
2
1.00
5.75
3
1.83
5.50
7
2.00
5.25
4
2.93
5.00
34
2.65
gery; the results would be somewhat greater after six months. • Average sphere was + 0.30 D. • Average cylinder was 0.90 D. • Average keratometry increased by 2.49 D. In addition: • Endothelial cell loss averaged 0.3%. • Induced astigmatism was greater than 1 D for four patients. To date, in our first 100 cases we have not had any microperforations, which may account for the low level of astigmatism postoperatively in these patients. Additionally, in tracking these patients, there has been no significant change in the endothelial cell count and there have been no complications to report. In our experience, side effects have been quite similar to those with radial keratotomy. In a few cases, we have patched longer than the first day because of some temporary corneal edema. And we caution the patients to protect their eyes from severe trauma even more so than in radial keratotomy, primarily because, unlike radial keratotomy, the hexagonal keratotomy incisions intersect and touch, weakening the unhealed eye. Finally, because of the intersecting incisions, hexagonal keratotomy requires exceptional surgical accuracy and skill. Extreme care must be taken to make incisions of proper depth. Thus, based on this wider study of 50 eyes (plus another 144 hexagonal keratotomy surgeries performed since then), our findings indicate that the results of hexagonal keratotomy surgery to date demonstrate the excellent promise of this procedure for hyperopic and presbyopic patients. Ronald P. Jensen, M.D.
Glendale, California
UNNECESSARY ALARM ABOUT LOVASTATIN AND CATARACTS To the Editor: The drug lovastatin is being marketed by Merck Sharp & Dohme under the trade name Mevacor®. This J CATARACT REFRACT
medication is a potent agent to lower serum levels of cholesterol; it works by inhibiting an enzyme that catalyzes an early rate-limiting step in cholesterol synthesis. Although some cataracts were produced in dogs given at least 50 times the maximum human dose for prolonged periods,l results in humans have been equivocal. Lovastatin appears to be only a weakly cataractogenic agent, if it is one at all, and only after years of administration. 2 A more recent report suggests that in fact lovastatinhas no adverse effects at all on the human lens. 3 Nevertheless, the manufacturers recommend initial and periodic ophthalmological examinations of patients taking this drug to check for cataract development. Material has appeared in the ophthalmological literature supporting this recommendation. 4 I question whether these exhortations really are in the patients' best interest. Patients taking lovastatin all have dangerously high levels of serum cholesterol. Such levels, it is now accepted, carry an unquestioned increased risk of cardiac and cardiovascular morbidity and mortality. Indeed, many of the patients I see have already suffered one or more myocardial infarctions, and a significant percentage have had coronary artery bypass surgery. These patients, when started on lovastatin, express concern about the apparent risk to their eyes and vision that perhaps is associated with the drug. I wonder if it is really necessary to frighten these patients in this way and to make them undergo the expense of periodic screening for cataracts that may be related only mildly to the use of this drug. Consider the extremely low morbidity and excellent recovery from modern cataract surgery and intraocular lens implantation. Contrast this with the life-threatening dangers of continued high cholesterol levels, usually in a subset of patients who already have had significant cardiac and! or cardiovascular morbidity. In these patients, I cannot conceive of any lens changes that would justify any reduction or elimination of this drug. Any patient who needs this drug should take it without concern for his or her visual future, grateful that he or she lives in an era in which such a medication is available. However, the prescribing physician must react to the package insert, and, in the medicolegal climate in which we live, badger the 20/20 patient into obtaining initial and periodic ophthalmological examinations. What is the point of such examinations? Any patient taking lovastatin (or any patient not taking lovastatin, for that matter) who has decreased vision should be encouraged to consult an ophthalmologist. Otherwise, patients ill enough to require lovastatin should not be forced to worry about "blindness" and the evils of cataracts. Let us hope that the federal authorities come to appreciate that the realities of modern cataract
SURG-VOL 14, SEPTEMBER 1988
.581