Prospective Clinical Study of Radial J<eratotomy VERINDER S. NIRANKARI, MD, LEEDS E. KATZEN, MD, RICHARD D. RICHARDS, MD, JAMES W. KARESH, MD, VINOD LAKHANPAL, MD, EMORY BILLINGS, BA
Abstract: A prospective clinical study of radial keratotomy was conducted at the University of Maryland. Results of surgery on 33 eyes of 19 patients with a minimum follow-up of seven months and a mean of 13.8 months are reported. There were eight patients (15 eyes) who needed adequate unaided visual acuity for occupational purposes. Preoperative visual acuity was 20/400 in 79% of eyes. Postoperative visual acuity was 20/50 or better in 48% of cases. However, in patients with preoperative refractive errors of 5 diopters or less, postoperative visual acuity was 20/50 or better in 84% of cases. Average decrease in myopia was 2.5 diopters. Decrease in myopia following radial keratotomy did not correlate with corneal curvature or whether 8 or 16 incision technique was used. However, there was a very significant (P = 0.001) difference in postoperative visual acuity of patients with refractive error of 5 diopters or less, as compared to those with greater than 5 diopters of myopia. Complications included corneal scarring, vascularization, and glare. No microperforation or endothelial cell loss was observed. [Key words: corneal curvature, endothelial cell loss, myopia, radial keratotomy, refractive error.] Ophthalmology 89:677 -683, 1982
Surgical correction of myopia by radial keratotomy has aroused great interest in the United States. Earlier studies by Fyodorovl and others2,3 have shown that myopia can be reduced but that the results are unpredictable and have significant side effects such as microperforations, endothelial cell loss, glare, and fluctuation in vision.2 ,3
A prospective clinical study of radial keratotomy was undertaken at the University of Maryland. Surgery was performed by one of us (LEK) at another hospital. Pre- and post-operative evaluations were done independently at the University Hospital.
From the Department of Ophthalmology, University of Maryland School of Medicine, Baltimore, Maryland.
Presented at the Eighty-sixth Annual Meeting of the American Academy of Ophthalmology, Atlanta, Georgia, November 1-6, 1981.
Reprint requests to Verinder S. Nirankari, MD, Cornea Service, University of Maryland, 22 S. Greene Street, Baltimore, MD 21201.
All patients undergoing radial keratotomy were informed of the experimental nature of the procedure and signed the approved informed consent. The unpredictable results of the surgery, as well as possible risks and complications, were explained in detail. Patients selected were 18 years and older, with at least a two-year history of stable refractive myopia of between 1.75-9 diopters, less than 2 diopters of astigmatism, and without any evidence of corneal disease. A major emphasis was placed on selecting candidates who were determined to enter occupations requiring specified visual acuity uncorrected by spectacles or contact lenses.
Independent evaluations of all patients were done before operation, one week, one month, three months, six months, and one year after operation, and included a detailed ophthalmic history, refractive error. corrected and uncorrected visual acuity, slit-lamp biomi-
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OPHTHALMOLOGY. JUNE 1982 • VOLUME 89 • NUMBER 6
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croscopy, pachymetry, keratometry, tonometry, and clinical specular microscopy. Surgery was performed as an outpatient procedure under topical anesthesia consisting of 0.5% proparacaine. The pupil was left in its normal state for the markings of the optical center. The patient was asked to fixate on the coaxial light that was shielded with a blue filter. Using a dull Russian
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Fig 3. Preop vision without correction.
CF
marking trephine of 3-mm size, the central clear zone was marked. The original blade used was a 76-A Beaver blade (later we switched to a Sputnik blade or Alcon feather blade). The blade was placed into a Katena Swiss blade holder at a depth equal to the central corneal thickness. The exact placement of the blade was set using the Bores and Kraemer blade
NIRANKARI, et al • RADIAL KERATOTOMY
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gauges. Sixteen incisions were used in the first 25 eyes and eight incisions in the last eight eyes. Initially, the incisions were carried 1 mm beyond the limbus into the sclera; later 1 mm of clear cornea at the limbus was left intact. The incision depth was checked with the Fyodorov depth gauge and deepened again if necessary. The incisions were irrigated with balanced salt solution. Gentamycin (3 mg/cc) and atropine (1% eyedrops were instilled, and the eye patched for 24 hours. Antibiotic steroid drops were used qid for two weeks.
RESULTS
Thirty-three eyes of 19 patients were involved in the study. These were consecutive patients with none lost to follow-up. Fourteen patients had bilateral surgery and five patients had unilateral surgery. There were nine women and ten men, and three patients (four eyes) had repeat surgery. These three patients had initially good results, but showed regression of their myopia decrease on follow-up over a three-month period. There were eight patients (15 eyes) who were operated upon who needed adequate unaided visual acuity for occupational purposes such as police force, flight school, merchant marines, etc. There were an additional four patients (seven eyes) who were contact lens failures. Patients ranged in age from 18 to 54 years, with a mean of 28 years. Follow-up varied from seven months to 23 months, with a mean of 13.8 months. Preoperative refractive error varied from -1.75 to -9.00 diopters, with a mean of -4.80 diopters (± 1.92) (Fig O. Postoperative refractive error varied from plano to -6.25 diopters, with a mean of -2.37 diopters (±1.99) (Fig 2). There was an average myopia decrease of 2.50 diopters, with a range of -0.50 to -6.75 diopters (±1.84).
Preoperative uncorrected visual acuity varied from 20/80 to count fingers with a majority (79%) being 201 400 or worse (Fig 3). Postoperative uncorrected visual acuity was 20/50 or better in 48% of eyes (Fig 4). Thirty-two out of 33 eyes had vision correctable to 20/20. One patient developed central corneal scarring and vision was correctable only to 20/30. Preoperative keratometry ranged from 41.25 to 46.75, with a mean
20/100 20/200 20/300 20/400
of 44.28 (± 1.40). Postoperative keratometry ranged from 39.62 to 45.75, with a mean of 42.77 (± 1.46) with an average decrease in K of 1.51 diopters (±1.09) (Fig 5). Patients were divided into two groups. Group 1 included patients with preoperative refractive errors of 5 diopters or less. There were 19 eyes of 11 patients, and 74% had 20/400 vision or worse (range 201 80-counting fingers). Sixteen of 19 eyes in this group (84%) achieved postoperative uncorrected vision of 20/50 or better (Fig 6). Group 2 included patients with greater than 5 diopters of myopia and constituted 14 eyes of nine patients. Seventy-one percent had preoperative vision of counting fingers (range 201 200-counting fingers). Only one patient in this group had postoperative uncorrected vision of 20/20 (Fig 7). The decrease in myopia in both the groups was, however, around 2.5 diopters. There were no corneal perforations during surgery. Endothelial cell photography by the Heyer Schulte specular microscope was done on 12 eyes of nine patients. The average preoperative central cell density was 2882 cells/mm2
• Follow-up specular microscopy at three months revealed no cell loss in any patient, with an average postoperative cell density being 2900 cells/mm2 • No determination could be made as to the correlation between the depth of the cuts to postoperative results. This was due to the fact that each cut was of a different depth and varied from
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Fig 6. Postop vision (uncorrected) of patients with preop refractive error of 5 diopters or less of myopia.
80 to 30% of the corneal thickness in the same eye as seen by slit-lamp biomicroscopy. Generally, the cuts were approximately 50% deep. This may be one reason we did not encounter any microperforations or endothelial cell loss.
The data was further analyzed using nonparametric statistical methods, including the Wilcoxon rank sum test, the Mann-Whitney test for comparison of unpaired samples, and Spearman rank correlation test for determining the degree of relationship between two dependent variables. The variables examined included pre- and post-operative visual acuity, pre- and postoperative refractive error, pre- and post-operative
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Fig 7. Postop vision (uncorrected) patients with preop refractive error of > 5 diopters of myopia.
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keratometry, corneal flattening, and surgical techniques using 16 or 8 radial cuts. There was no significant difference in either postoperative visual acuity or postoperative refractive error when either 8 or 16 radial incision technique was used. A good positive correlation (r 2 = +.707) was shown to exist between pre- and post-operative keratometric values (Fig 8). However, preoperative keratometric values could not be correlated to either postoperative visual acuity or postoperative refractive error. A fair positive correlation (r2 = + .523) was shown between preoperative refractive error and postoperative visual acuity. Pre- and post-operative refractive errors also demonstrated a moderate to good positive relationship (r2 = + .643) (Fig 9), but no correlation could be found between preoperative refractive error and postoperative keratometry values. The preoperative refractive errors of the patients were then examined by separating them into two groups. Patients in Group 1 had preoperative refractive errors equal to or less than 5 diopters, and Group 2 patients had greater than 5 diopters of refractive error. No significant difference could be found in the amount of corneal flattening achieved by these groups. However, there was a very significant (P = 0.001) difference between the postoperative visual acuity achieved by these two groups. The median visual acuity of those in group 1 was 20/30 and those in group 2 was 20/200. An examination was made to de-
NIRANKARI, et al • RADIAL KERATOTOMY
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termine if there was any difference between patients with postoperative visual acuities of 20/50 or better and those with postoperative visual acuities of less than 20/50. The amount of corneal flattening achieved by each of these groups could not be shown to be significantly different. However, the preoperative refractive errors of these two groups were significantly different (P = 0.001). Those patients with postoperative visual acity of 20/50 or better had a lower mean preoperative refractive error (3.64 diopters) than those with postoperative visual acuity ofless than 20/50 (5.85 diopters).
Complications in these patients included regression of flattening that usually occurred within the first three months, epithelial cysts in the keratotomy scars, scars along the incisions, deep corneal vascularization along
the incisions, 2 mm inside the limbus that have not shown any progression, and central corneal scarring (Table 1). Central corneal scarring occurred in three eyes, all of which had central corneal erosions and keratitis following surgery, with resultant central anterior stromal scarring (Fig 10). However, only one patient had decrease to 20/30 in her best corrected visual acuity. Significant glare was not a problem in our study. One patient complained of glare weeks after surgery, but eight months later had only mild glare, noted especially at night. Variable vision was seen in most patients immediately following surgery, with vision being better in the morning and worse in the night, but this problem disappeared on follow-up in 30/33 eyes. Only three eyes (two patients) complained of variable vision on long-term follow-up .
Fig 9. Comparison of pre- and post-operative refractive errors indicating a moderately good positive correlation. Spearman rank correlation 's = +.643 .
DISCUSSION
Surgical correction of myopia by radial keratotomy remains a highly controversial procedure. This ongoing study was conducted to clarify whether this procedure was effective and predictable and what complications occurred, both short- and long-term. The data on the first 33 eyes of 19 patients with a minimal follow-up of seven months (mean 13.8 months) were studied. There were eight patients (15 eyes) who were entered into this study who desired unaided visual acuity of approximately 20/50 in one eye and 20/100 in the other eye for occupational needs. There were an additional four patients (seven eyes) who were contact lens failures.
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Table 1. Complications of Radial Keratotomy
Perforations Epithelial cysts Deep corneal vascularization Central scarring
0/33 4/33 2/33 3/33
In agreement with earlier studies , we could not find any difference in the results with 8 vs 16 cutS.4- 6 The depth of the cuts were approximately 50% in most cases. This was in spite of the fact that the blade setting was 100% of the central corneal thickness. No endothelial cell loss has been observed in our patients .
Fig 10. Left eye showing central corneal scarring.
NIRANKARI, et al • RADIAL KERATOTOMY
This is in contradistinction to earlier reports,2,3 but both these studies showed a significant rate of microperforation (15-20%) and also the depth of their cuts were 80-90% of the corneal thickness, which may account for this variance. However, as there is a possibility of continuing cell loss following surgery, 7
long-term follow-up is essential to clarify this observation. Forty-eight percent of patients achieved 20150 or better vision. However, if patients with a myopia of 5 diopters or less are considered, then 84% of these achieved vision of 20150 or better. There was a significant difference (P < 0.001) between this group and those with myopia of >5 diopters. Only one patient (one eye) failed to achieve vision correctable to 20/20. She showed central corneal scarring and vision was correctable to 20/30 (Fig 10). Glare was not a major problem in our study, and only one patient complained of glare and then only at night.
In our study, patients with a refractive error of 5 diopters or less are the most likely candidates to achieve satisfactory results with this procedure, irrespective of their keratometric values, or whether they had 8 or 16 radial incisions. It is our opinion, based on evaluating 33 eyes with a mean follow-up of 13.8 months, that this procedure does result in lessening of myopia and improvement of vision, especially in myopes of 5 diopters or less. However, long-term follow-up and both extensive clinical and experimental
studies, which are now in progress, are essential before the long-term efficacy of this procedure can be accurately assessed.
REFERENCES
Fyodorov SN, Durnev VV. Operation of dosaged dissection of corneal circular ligament in cases of myopia of mild degree. Ann Ophthalmol 1979; 1'1:1885-90.
3. Cowden JW, Bores LD. A clinical investigation of the surgical correction of myopia by the method of Fyodorov. Ophthalmology 1981; 88:737-41.
4. Schachar RA, Black TO, Huang T. A physicist view of radial keratotomy with practical surgical implications. In: Schachar RA, Levy NS, Schachar L, eds Keratorefraction. Denison. Texas: LAL publishing , 1980; 195-220.
5. Jester JV, Venet T, Lee J, et al. A statistical analysis of radial keratotomy in human cadaver eyes. Am J Ophthalmol 1981 : 92:172-7.
6. Jester JV, Steel D, Salz J, et al. Radial Keratotomy in non· human primate eyes. Am J Ophthalmol1981 ; 92:152-71.
7. Yamaguchi T, Polack FM, Safer A, et al. Electron microscopic study of anterior radial keratotomy on monkey and rabbit corneas. ARVO Abstracts. Invest Ophthalmol Vis Sci 1981; 20(Suppl):68
