Year : 1983 | Volume
: 31 | Issue : 7 | Page : 860--865
Ongoing prospective clinical study of radial keratotomy
Verinder S Nirankari, Leeds E Katzen, James W Karesh, Richard, D Richares, Vinod Lakhanpal
Department of Ophthalmology, University of Maryland, School of Medicine, Baltimore, Maryland, USA
Verinder S Nirankari
Department of Ophthalmology, 22 S Greene Street, Baltimore, Maryland-21201
|How to cite this article:|
Nirankari VS, Katzen LE, Karesh JW, Richard, Richares D, Lakhanpal V. Ongoing prospective clinical study of radial keratotomy.Indian J Ophthalmol 1983;31:860-865
|How to cite this URL:|
Nirankari VS, Katzen LE, Karesh JW, Richard, Richares D, Lakhanpal V. Ongoing prospective clinical study of radial keratotomy. Indian J Ophthalmol [serial online] 1983 [cited 2021 Jun 13 ];31:860-865
Available from: https://www.ijo.in/text.asp?1983/31/7/860/29687
Over the past several years radial keratotomy for the correction of myopia has been the subject of much interest and controversy amongst ophthalmologists. Despite its increasing use, the results of such surgery remain unpredictable,,. In addition, the varying amounts of myopia reduction achieved by this type of keratorefractive surgery are often accompanied by post-operative side effects including glare, fluctuating vision, mieroperforations, endophthalmitis, endothlial cell loss, and corneal scarring,,,,,.
A prospective study of radial keratotomy has been ongoing at the University of Maryland, School of Medicine, for the past three years. Surgery was performed by one of the authors (LEK) at another hospital. Patients were evaluated independently both preand post-operatively at University Hospital. We report here our additional experience with this procedure.
MATERIALS AND METHODS
The surgical technique and research protocol have been previously described.
Patients selected were all at least 18 years of age, had 1.75 to 12.50 diopters of stable myopia with a maximum of 2.50 diopters of astigmatism, and had no evidence of any ocular disease. A major emphasis was placed on selecting patients who required specified uncorrected visual acuity in order to enter a variety of occupations (fireman, policeman, F.B.I. agents, pilots, merchant marines, etc.).
Patients were independently evaluated preoperatively, and at one week, one month, three months, six months, one year, two years, and three years post-operatively. Examination included a complete ophthalmic history, refraction, determination of corrected and uncorrected visual acuity, slit lamp biomicroscopy, keratometry, tonometry, and specular microscopy.
Changes from our previously reported surgical techniques included the use of a diamond blade instead of an Alcon feather blade or Sputnick blade and increased use of 8 instead of 16 incisions over the past 12 months. A 3 mm central optical zone continued to be utilized. The incisions were carried from the central optical zone to within 1 mm of the limbus. Reoperations were carried out by either deepening existing incisions or creating 8 new incisions.
The data was analyzed using the Pearson's product moment correlation, the Chi-square statistic with Yates' correction, and the Student's t-test.
Patients ranged in age from 19 to 57 years with a mean of 32 years. There were 23 males and 10 females. All were consecutive patients with none lost to follow-up. There were 52 eyes that underwent a single operation and six eyes (five patients) that underwent two operations. The latter group was analyzed separately. Follow-up varied from six months to 38 months with a mean of 19 months. Fifty percent of operated eyes had 8 radial incisions and fifty percent had 16 radial incisions. Preoperative uncorrected visual acuity ranged from 20%70 to count fingers. The majority of patients (74%) had 20/400 or worse uncorrected visual acuity. In all cases preoperative visual acuity could be corrected to at least 20/20 with the appropriate refractive error correction. Preoperative refractive errors ranged from-1.75 diopters to-12.25 diopters (mean-4.63 diopters). Preoperative keratometry ranged from 40.74 diopters to 46.75 diopters (mean 44.04 diopters).
Post-operatively, uncorrected visual acuity varied from 20/20 to 20/400. A vision of 20/40 or better was achieved by 48% of the operated eyes. A comparison of preoperative and postoperative visual acuity is seen in [Figure 1]. Refractive errors ranged from +3.25 diopters to-8.25 diopters (mean-1.93 diopers). Errors between +.75 diopters and-1.00 diopters were present in 43% of the operated eyes. A comparison of preoperative and post-operative refractive error is seen in [Figure 2]. The average change in refractive error was 2.70 diopters of myopia decrease. [Figure 3]. This was highly significant (p 5sub when compared to our second 25 eyes, when comparing final visual acuity, chagne in refractive error or in the degree of corneal flattening.
Six eyes (five patients) in our study were reoperated. Three eyes had initial good visual results, but regressed over a three-month period. The other three eyes did not show an adequate change in visual acutiy or refractive error following the initial surgery. All of these patients desired good uncorrected visual acuity for occupational purposes. In three cases surgery consisted of deepening the original 16 incisions, and in the other three cases where 8 incisions had been made initially, 8 new incisions were made. In these six eyes, the first procedure resulted in an average of 2.52 diopters change in refractive error, while the second procedure resulted in an additional average change of 1.12 diopters of myopia. Following this procedure, two eyes still failed to achieve a final uncorrected visual acuity of 20/50 or better. In both these eyes their refractive myopia increased after the second surgery. In one from-1.75 diopters to-3.25 diopters and in the other from3.00 diopters to-4.00 diopters.
Complications encountered in our patients included symptoms of glare and fluctuating vision. In all patients these symptoms completely resolved over a six month period, except for one patient who complained of glare after eight months but not after one year. The depth of the radial incisions varied from 30% to 80% of corneal thickness in the same eye, with an average depth of 50%. There were no microperforations in our series. Three patients had central scarring associated with corneal erosions and keratitis following surgery. Only one of these patients achieved a decreaes in best corrected vision to 20/30. All other patients achieved a best corrected vision of at least 20/20. Endothelial cell photography by the Heyer Schulte specular microscope was done on 22 eyes of 15 patients. Only one patient showed an 11% loss of endothelial cells at three months follow-up examination. One patient was overcorrected to a +3.50 diopter refractive error. Five patients developed post-operative cylinders of 1.50 to 2.50 diopters. Seven eyes showed regression of their post-operative refractions to within 1 diopter or less of their preoperative refractrions. As previously reported, epithelial cysts, dense scarring along the radial incisions, and deep corneal vascularization along the incisions were also seen [Table 1].
Radial keratotomy for the correction of myopia remains a controversial procedure. The present study was undertaken to determine the long term safety and efficacy of this procedure as weel as the factors that might predict its outcome. Over the past 12 months an additional 25 eyes of 14 patients have been examined in our prospective study of radial keratotomy. This brings a total to 58 eyes in 33. patients with an average follow-up of 19 months.
Unlike other reports,, there were no microperforations in our series and only one incidence of endothelial cell loss. This is probably related to the depth of the incision in our cases (average of 50% of corneal thickness) when compared to those in the other seriers (80 to 90% of corneal thickness).
Surgical overcorrection and post-operative cylinder did occur in a small number of cases, as did regression of the initial refractive changes. In the six eyes where a second procedure was performed, on the average, and additional 1.12 diopter of change was achieved. The reasons behind the occurrence of this small additional change remain unclear. Glare and fluctuating vision, while a problem in the short term, failed to remain a ,problem beyond a six to 12 month operative period.
Like other reports,,, no difference in postoperative results could be found between 8 and 16 radial incisions. The average change in refractive error for all 58 eyes was 2.70±.34 diopters. Possibly a greater change could be effected with deeper cuts. However, the risk of microperforations, endophthalmitis, and endothelial cell loss would probably be increased. A continuing problem was the inability to control the depth of incisions despite knowledge of corneal thickness, the conscious effort ofthe surgeon, and the appropriate setting of the blade length equal to the central corneal thickness.
A major difficulty with radial keratotomy is the inability to predict surgical results. Earlier studies have been unable to relate such factors as corneal thickness, number or depth of incisions or preoperaive keratometry measurements to changes in refractive error or vision,,. However, we were able to predict with a high degree of accuracy (p<.001) the average amount of change in both refractive error (2.70±.34 diopters) and keratometric measurements (1.51±.30 diopters) that could be obtained by radial keratotomy as performed in our institution. These data explain the significant (p<.005) difference in the visual results achieved by eyes with 5 diopters or less of myopia and eyes with greater than 5 diopters of myopia. Smaller refractive errors will be closer to emmetropia following the procedure. Therefore, these eyes will have better visual acuities.
Our ongoing study of radial keratotomy confirms that this procedure results in a reduction of refractive myopia and a flattening of the cornea. Continuing problems appear to be whether the results of such surgery can be accurately predicted, whether such results can be maintained over the long term, and the effect of this procedure on corneal function.
The ongoing prospective clinical study of radial keratotomy at the University of Maryland now includes 58 eyes of 33 patients. 52 eyes underwent a single operation, whereas six eyes underwent two operations. Follow-up was a minimum of six months and a mean of 19 months. Preoperative vision was 20/400 or less in 74% of eyes. Post-operative vision was 20/40 or better in 48% of eyes. There was an average myopia decrease of 2.70 diopters and an average corneal flattening of 1.51 diopters. Patients with preoperative refractive errors of 5 diopters or less achieved 20/40 or better vision in 65% of eyes, as compared to only 19% in eyes with preoperative refractive errors greater than 5 diopters. This is highly significant (p<.005). There was no difference in the results achieved by our first 33 eyes when compared to our second 25 eyes. The decrease in myopia did not correlate with corneal curvature, or whether 8 or 16 incisions had been used. No microperforations were seen and only one case of endothelial cell loss was observed. Glare and fluctuating vision was not a significant problem in our series.
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