Journal of Refractive Surgery

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Retrospective Comparison of Simultaneous and Non-Simultaneous Bilateral Radial Keratotomy

Hamilton Moreira, MD; Amir H Kolahdouz-Isfahani, MD; Joseph S Englanoff, MD; Arman P Fasano, MD; Argyrios Ziogas, MS; Richard Villaseñor, MD; Peter J McDonnell, MD

Abstract

ABSTRACT

PURPOSE: Many radial keratotomy surgeons advocate bilateral simultaneous surgery, in which there is an inherent, although rare, risk of bilateral sight-threatening complications such as microbial keratitis. This study was designed to evaluate the refractive outcomes of simultaneous and nonsimultaneous radial keratotomy performed by a single surgeon.

METHODS: We retrospectively compared the results of radial keratotomy performed simultaneously (both eyes operated on the same day, 20 patients) versus non-simultaneously (right and left eyes operated on different days, 71 patients) by a single surgeon. Both eyes had the same surgical procedure, including clear zone diameter and number of incisions.

RESULTS: The refractive results of bilateral simultaneous and non-simultaneous surgery were largely equivalent for all parameters analyzed except one. The variability of the difference in postoperative refractive error between right and left eyes was less for those patients undergoing simultaneous surgery (p = .0008).

CONCLUSION: Our data suggest that performing radial keratotomy as a bilateral simultaneous procedure increases the symmetry of the refractive effect. In view of recent reports of sight-threatening risks such as bilateral microbial keratitis following bilateral keratotomy, however, the potential risks and benefits of bilateral surgery should be carefully considered before operating on both eyes on the same day. [J Refract Corneal Surg. 1994;10:545-549. J

RESUME

INTRODUCTION: Bien des chirurgiens de la kératotomie radiaire recommandent la chirurgie bilatérale en même temps, ce qui entraine une risque, quoique rare, de kératite infectieuse bilatérale. Cette étude a été fait afin d'évaluer les résultats réfractifs de la kératotomie radiaire bilatérale achevée par le même chirurgien, simultanément et individuellement.

METHODES: Nous avons comparé rétrospectivement les résultats de la kératotomie radiaire bilatérale réalisée simultanément sur 29 patients avec ceux réalisée dans les deux yeux sur les jours différents. Les deux yeux ont subi exactement la même chirurgie, ce qui inclut la taille de la zone optique et nombre d'incisions, par le même chirurgien.

RESULTATS: Les résultats réfractifs de Ia chirurgie bilatérale simultanée et non-simultanée furent équivalentes dans tous les paramètres analysés sauf un. La variation dans la différence d'erreur refractive entre l'oeil droit et gauche est moindre chez les patients opérés simultanément (p = 0,0008).

CONCLUSIONS: Nos données suggèrent que la réalisation de la kératotomie radiaire biltérale et simultané entraîne un effet réfractif plus symétrique. Cependant, en vue des comptes rendus des risques menaçant Ia vision, comme Ia kératite infectieuse bilatérale, les risques et les avantages de la chirurgie bilatérale simultanée doivent êtres considérés avant d'opérer les deux yeux simultanément. (Translated by Robert Mack, MD, Kansas City, Mo.)

SOMMARIO

PREMESSA: Una significativa percentuale di chirurghi di cheratotomia radiale propugnano l'intervento bilaterale e simultaneo, sebbene consci dei possibili, rari, rischi di compromissione funzionale bilaterale, o di cheratiti infettive. Scopo di questo studio é di valutare i risultati refrattivi della simultanea e non simultanea cheratotomia radiale effettuata da uno stesso operatore.

METODI: Noi abbiamo retrospettivamente comparato i risultati della cheratotomia radiale effettuata dal medesimo chirurgo simultaneamente (entrambi gli occhi di 29 pazienti operati il medesimo giorno) con i risultati ottenuti in interventi non simultanei (gli occhi di 71 pazienti operati in giorni diversi). Entrambi gli occhi hanno subito la medesima tecnica chirurgica, compresa la stessa zona ottica ed il medesimo numero delle incisioni.

Abstract

ABSTRACT

PURPOSE: Many radial keratotomy surgeons advocate bilateral simultaneous surgery, in which there is an inherent, although rare, risk of bilateral sight-threatening complications such as microbial keratitis. This study was designed to evaluate the refractive outcomes of simultaneous and nonsimultaneous radial keratotomy performed by a single surgeon.

METHODS: We retrospectively compared the results of radial keratotomy performed simultaneously (both eyes operated on the same day, 20 patients) versus non-simultaneously (right and left eyes operated on different days, 71 patients) by a single surgeon. Both eyes had the same surgical procedure, including clear zone diameter and number of incisions.

RESULTS: The refractive results of bilateral simultaneous and non-simultaneous surgery were largely equivalent for all parameters analyzed except one. The variability of the difference in postoperative refractive error between right and left eyes was less for those patients undergoing simultaneous surgery (p = .0008).

CONCLUSION: Our data suggest that performing radial keratotomy as a bilateral simultaneous procedure increases the symmetry of the refractive effect. In view of recent reports of sight-threatening risks such as bilateral microbial keratitis following bilateral keratotomy, however, the potential risks and benefits of bilateral surgery should be carefully considered before operating on both eyes on the same day. [J Refract Corneal Surg. 1994;10:545-549. J

RESUME

INTRODUCTION: Bien des chirurgiens de la kératotomie radiaire recommandent la chirurgie bilatérale en même temps, ce qui entraine une risque, quoique rare, de kératite infectieuse bilatérale. Cette étude a été fait afin d'évaluer les résultats réfractifs de la kératotomie radiaire bilatérale achevée par le même chirurgien, simultanément et individuellement.

METHODES: Nous avons comparé rétrospectivement les résultats de la kératotomie radiaire bilatérale réalisée simultanément sur 29 patients avec ceux réalisée dans les deux yeux sur les jours différents. Les deux yeux ont subi exactement la même chirurgie, ce qui inclut la taille de la zone optique et nombre d'incisions, par le même chirurgien.

RESULTATS: Les résultats réfractifs de Ia chirurgie bilatérale simultanée et non-simultanée furent équivalentes dans tous les paramètres analysés sauf un. La variation dans la différence d'erreur refractive entre l'oeil droit et gauche est moindre chez les patients opérés simultanément (p = 0,0008).

CONCLUSIONS: Nos données suggèrent que la réalisation de la kératotomie radiaire biltérale et simultané entraîne un effet réfractif plus symétrique. Cependant, en vue des comptes rendus des risques menaçant Ia vision, comme Ia kératite infectieuse bilatérale, les risques et les avantages de la chirurgie bilatérale simultanée doivent êtres considérés avant d'opérer les deux yeux simultanément. (Translated by Robert Mack, MD, Kansas City, Mo.)

SOMMARIO

PREMESSA: Una significativa percentuale di chirurghi di cheratotomia radiale propugnano l'intervento bilaterale e simultaneo, sebbene consci dei possibili, rari, rischi di compromissione funzionale bilaterale, o di cheratiti infettive. Scopo di questo studio é di valutare i risultati refrattivi della simultanea e non simultanea cheratotomia radiale effettuata da uno stesso operatore.

METODI: Noi abbiamo retrospettivamente comparato i risultati della cheratotomia radiale effettuata dal medesimo chirurgo simultaneamente (entrambi gli occhi di 29 pazienti operati il medesimo giorno) con i risultati ottenuti in interventi non simultanei (gli occhi di 71 pazienti operati in giorni diversi). Entrambi gli occhi hanno subito la medesima tecnica chirurgica, compresa la stessa zona ottica ed il medesimo numero delle incisioni.

Radial keratotomy has been performed in the United States since November 1978. * Over the years, numerous improvements in surgical technique, as well as in prospective evaluation of individual patient variables, have been incorporated to try to improve the outcome of this procedure.24 Despite all of these modifications, however, predicting the change in refraction after radial keratotomy remains limited.5 To more accurately predict the outcome of radial keratotomy, the surgeon must attempt to achieve a reproducible surgical technique, but must also consider the variabilities of age and individual wound healing. It is primarily because of this latter variable that surgeons who perform radial keratotomy today often prefer non-simultaneous surgery; this way, results of the first eye can be examined before operating on the second eye.6 Other ophthalmologists, however, are proponents of a single procedure, whereby both eyes undergo radial keratotomy in one sitting.7 Perhaps it is surmised that predictability of outcome is improved since a more uniform procedure is performed, compared to nonsimultaneous surgery. Furthermore, since over 90% of individuals with preoperative refractive errors have a discrepancy of =sl.00 diopter (D) between the two eyes,8 it is conceivable that a simultaneous procedure would yield greater symmetry of effect postoperatively than would a nonsimultaneous procedure.

Herein we present the results of radial keratotomy performed simultaneously and non-simultaneously. A comparison of the change in refraction after radial keratotomy, the accuracy of predictability, and the symmetry of effect are evaluated.

Table

Table 1Data on Two Groups of Patients Receiving Bilateral Radial Keratotomy (RK)

Table 1

Data on Two Groups of Patients Receiving Bilateral Radial Keratotomy (RK)

MATERIALS AND METHODS

We reviewed a computerized data base that listed patients who had undergone bilateral radial keratotomy performed by the same surgeon (R. V.) between July 1982 and February 1989. All surgeries consisted of either four or eight radial incisions, without any transverse incisions.

Surgical Technique

A diamond knife was set at 100% of the thinnest paracentral corneal thickness as measured by an ultrasonic pachometer. The clear zone diameter varied between 3.00 and 5.00 mm, with 0.25millimeter increments, depending on the preoperative refractive error. The clear zone was marked by using a visual axis marker of appropriate diameter centered on the corneal light reflex while the patient fixated on a coaxial fiberoptic light source mounted within the operating microscope. Radial incisions were initiated at the edge of the marked clear zone and extended peripherally to within 0.5 mm of the limbus (centrifugal direction).

Population

All patients had undergone either simultaneous or non-simultaneous bilateral radial keratotomy. Simultaneous bilateral radial keratotomy was performed on 29 patients who desired simultaneous surgery because it was more convenient for them or because they were unable to make two long trips to the Los Angeles area. However, only 20 patients had a minimum postoperative follow-up period of greater than or equal to 1 year. The patients' ages ranged from 18 to 61 years, with a mean age of 37.0 ± 11.8 years (mean ± standard deviation); there were 11 women and 9 men (Table 1). The range of cycloplegic refractive errors preoperatively was -2.13 to -9.13 (spherical equivalent refraction). The order in which radial keratotomy was performed on the two eyes of each patient was randomly assigned and designated as eye #1 or eye #2 for the purpose of statistical analysis.

The data base was searched to find patients who had undergone non-simultaneous bilateral keratotomy and who matched the simultaneous patients for sex, age (within 2 years), refractive error (within 0.50 D), no transverse incisions, and a minimum postoperative follow-up period of greater than or equal to 1 year for each eye. This non-simultaneous bilateral surgery group consisted of 71 patients whose ages ranged from 20 to 59 years (mean, 36.9 ± 9.0 years); there were 37 women and 34 men (Table 1). The range of cycloplegic refractive error preoperatively was -1.25 to -9.50 (spherical equivalent refraction). Radial keratotomy was performed first on the nondominant eye, designated as eye #1, in this group.

Table

Table 2Pre- and Postoperative Refractive Errors (D, Mean ± SD) in Two Groups of Patients Receiving Bilateral Radial Keratotomy (RK)

Table 2

Pre- and Postoperative Refractive Errors (D, Mean ± SD) in Two Groups of Patients Receiving Bilateral Radial Keratotomy (RK)

The refractive error that was taken at the time of the last office visit was used as the postoperative result and also as the endpoint of the follow-up period. Refractive errors are presented as the spherical equivalent refraction. Chi square, Wilcoxon rank sums test, F-test, and nonparametric analysis of variance (ANOVA) were performed. Significance level was defined as p ≤ .05.

RESULTS

There was no significant difference in the number of four- and eight-incision surgeries performed between the two groups. The most frequently used clear zone diameter in both groups was 3.00 mm, and the distribution between the two groups was not significantly different.

The average follow-up periods in the nonsimultaneous and simultaneous groups were 36. 1 ± 17.8 and 41.6 ± 19.4 months (mean ± standard deviation), respectively, which was not a statistically significant difference (Table 1).

The average preoperative refractive errors for eye #1 in the non-simultaneous and simultaneous groups were -4.27 ± 1.61 D and -5.09 ± 2.32 D, respectively; this difference was not statistically significant. The average preoperative refractive errors for eye #2 in the non-simultaneous and simultaneous groups were -4.14 ± 1.57 D and -4.93 ± 2.15 D, respectively; this difference was also not statistically significant (Table 2).

The average postoperative refractive errors for eye #1 in the non-simultaneous and simultaneous groups were -0.37 ± 1.00 D and -0.35 ± 1.54 D, respectively; this difference was not statistically significant. The average postoperative refractive errors for eye #2 in the non-simultaneous and simultaneous groups were -0.27 ± 1.29 D and -0.34 ± .70 D, respectively; this difference was also not statistically significant (Table 2).

Table

Table 3Postoperative Difference in Refractive Error (D) Between Right and Left Eye*

Table 3

Postoperative Difference in Refractive Error (D) Between Right and Left Eye*

The mean postoperative refractive error in eye #2 of the non-simultaneous group was analyzed against the mean postoperative refractive error of both eyes in the simultaneous group. The values were - 0.27 ± 1.29 D and -0.34 ± 1.60 D, respectively; no statistically significant difference was noted.

Symmetry in postoperative refraction between the two groups was analyzed by calculating the difference between postoperative refractive error in eye #1 and eye #2 of each group. The mean differences between eye #1 and eye #2 in the non-simultaneous and simultaneous groups were -0.10 ± 1.23 D and - 0.01 ± 0.54 D, respectively, and these values were not significantly different. However, the difference between the standard deviations, 1.23 and 0.54, was statistically significant (p < .0001). Furthermore, the mean difference between eye #1 and eye #2 of both groups was calculated only for those eyes in which the preoperative refractive error differed by 1.00 D or less. With this condition, the mean differences in the postoperative refractive error between eye #1 and eye #2 in the non-simultaneous and simultaneous groups were -0.13 ± 1.24 and -0.04 ± 0.55, respectively (Table 3). The mean difference was not significantly different, yet once again the standard deviation difference, 1.24 and 0.55, was statistically significant (p < .0008) (Figure).

Overcorrection was defined as postoperative refractive error of +1.00 D or greater. The overall overcorrection rates in the non-simultaneous and simultaneous groups were 8.5% and 12.5%, respectively, and these values were not significantly different. Within the non-simultaneous group, the overcorrection rate in eye #2 was 11.3%, which was twice the rate of overcorrection in eye #1 (5.6%) (Table 4). However, this difference was not statistically significant.

Figure: The postoperative refractive error difference between the right and left eyes of those patients with a preoperative refractive error difference between eyes of «1.00 diopter, demonstrating the increased symmetry of effect associated with simultaneous radial keratotomy.

Figure: The postoperative refractive error difference between the right and left eyes of those patients with a preoperative refractive error difference between eyes of «1.00 diopter, demonstrating the increased symmetry of effect associated with simultaneous radial keratotomy.

Undercorrection was defined as postoperative refractive error of - 1.00 D or less. The overall undercorrection rates in the non-simultaneous and simultaneous groups were 18.3% and 32.5%, respectively, and this difference was not statistically significant (p = .053). Within the non-simultaneous group, the undercorrection rate in eye #2 was 22%, and the rate of undercorrection in eye #1 was 14%. However, this difference was not statistically significant.

DISCUSSION

A major drawback to radial keratotomy is the inability to accurately predict the outcome. As reported in the PERK Study, the width of the prediction 90% interval for the refractive change was 4.42 D.5 With radial keratotomy for myopic correction, where the surgery is elective and alternative means of optical correction exist, many believe the degree of predictability of outcome should be higher. In an attempt to enhance this predictability, some surgeons advocate a non-simultaneous procedure.6 Taking into consideration the variability of individual wound healing, the non-dominant eye initially undergoes radial keratotomy and then, depending on the change in refraction after this procedure, adjustments are made to optimize the results of the second procedure, which is performed on the dominant eye.

Contrary to this view, there are those who prefer to perform a single, simultaneous radial keratotomy procedure.7 Some possible advantages to this approach are: not subjecting the patient to the expense or inconvenience of two procedures; and postoperative symptoms such as pain and photophobia, although intensified, are experienced only once. Furthermore, in their opinion, consistency of surgical technique can negate the variability of individual wound healing, thereby producing optimal refractive change with radial keratotomy. The sharpness of the blade, the steadiness of the surgeon's hand, and so on are presumed to be less varied in one sitting. Therefore, a surgeon applying these principles, along with an appropriate nomogram for an individual patient, might be more likely to produce more consistently symmetrical results than if done in two separate procedures.

Table

Table 4Percentage of Overcorrections

Table 4

Percentage of Overcorrections

In our study of 71 patients who underwent nonsimultaneous radial keratotomy and 20 patients who underwent simultaneous radial keratotomy, an analysis of the data was performed to address the relative merits of non-simultaneous versus simultaneous surgery. Initially, a comparison of the overall refractive change after radial keratotomy was performed, regardless of whether it was the first or second eye to be operated on. Taking into account that the difference in the preoperative refractive error among the two patient groups was not statistically significant, the results showed that the overall difference in refractive error postoperatively among the two patient groups was likewise not statistically significant. Therefore, it appears that performing radial keratotomy simultaneously on both eyes in one sitting does not improve the accuracy of predicting the outcome of radial keratotomy.

The issue of adjusting for individual wound healing by observing the outcome of the first eye and then modifying one's technique upon operating on the second eye was also addressed. How would the results of the change in refraction of the second eye in the non-simultaneous group compare with those in the simultaneous group? In approaching this, one has to first appreciate the fact that in the simultaneous group there is actually no "first* or "second" eye. Both eyes are operated on in one sitting, so the combination of both eyes can represent either the "first" or "second" eye. Keeping this in mind, as well as once again noting no statistically significant difference in preoperative refractive error, we compared the postoperative results of the second eye of the non-simultaneous group with the combined postoperative results of the simultaneous group. We found no statistically significant difference between the two. Once again, we were able to show that performing radial keratotomy on both eyes in one sitting does not improve the outcome as compared with non-simultaneous radial keratotomy. On the other hand, to our surprise, these results showed also that there was no measurable benefit to the second eye in performing non-simultaneous radial keratotomy. The theory of improving the outcome of the second eye by observing the results of surgery on the first eye was not supported.

Another issue pursued was that of symmetry of results following radial keratotomy. Although anisometropia is not a major complication of this surgery, the PERK Study showed that 14% of patients had four to eight Snellen lines difference in the uncorrected visual acuity between their two eyes, while only 1% of the patients had this great of a discrepancy prior to surgery.8 This emphasizes the potential clinical problem of asymmetry of refraction induced by radial keratotomy. Keeping this in mind, and remembering that the majority of patents who undergo radial keratotomy have symmetrical myopia before surgery, it would appear logical to assume that simultaneous radial keratotomy would yield greater symmetry of results than would nonsimultaneous radial keratotomy. To assess this, patients from each group who had a preoperative refractive error difference of ^1.00 D between eyes were classified as having symmetrical myopia and were selected for this analysis. Of the 71 patients in the non-simultaneous group, 57 met this requirement, as did 17 of 20 patients in the simultaneous group. A comparison of the mean postoperative refractive error differences between eye #1 and eye #2 of the two groups showed no statistically significant difference. However, in comparing the standard deviations of the postoperative refractive error differences between eye #1 and eye #2 of the two groups, a statistically significant difference was shown p < .0008). The postoperative refractive error differences between eyes #1 and #2 were less variable in the simultaneous group. Therefore, the concept of simultaneous radial keratotomy yielding a more reproducible surgical result is supported, and it appears that performing radial keratotomy simultaneously does increase the symmetry of effect.

One final point of concern that we addressed in our study was the issue of overcorrection. Overcorrection, especially in patients with presbyopia, is a common and particularly undesirable complication of radial keratotomy. Those surgeons who advocate non-simultaneous radial keratotomy might have the advantage of forewarning by awaiting the results of the first eye. Therefore, they would presumably generate fewer overcorrections as a whole, and fewer bilateral overcorrections, in comparison to those surgeons who perform simultaneous radial keratotomy. To assess this, patients from each group with a postoperative refractive error S= + 1.00 D in either eye were considered to be overcorrected. A comparison between the simultaneous and non-simultaneous groups of these overcorrected patients showed no statistically significant difference between the two. Hence, it appears from the results of this study that performing radial keratotomy in two separate sittings does not protect one from the miscalculations of overcorrection. In like manner, these results do not demonstrate a relative increase in overcorrection by performing simultaneous radial keratotomy.

Based on our findings, it appears that simultaneous radial keratotomy enhances symmetry of results when compared to non-simultaneous radial keratotomy. All other parameters analyzed showed no significant difference. The possibility of a severe occurrence, such as microbial keratitis, that would complicate the procedure and endanger both eyes must be weighed against the possible benefits of bilateral simultaneous surgery. Because serious, vision-threatening complications of radial keratotomy are uncommon (less than 1%), our small study would not be expected to include such problems. Nevertheless, occasional patients may suffer bilateral microbial keratitis with visual loss after bilateral surgery.9

This a retrospective study, with the limitations inherent to such studies. A prospective, randomized clinical study comparing simultaneous versus nonsimultaneous radial keratotomy would be necessary to unequivocally compare the results achieved. Whether such a study would be justified in light of the possibility of bilateral complications is a matter of controversy.

REFERENCES

1. Arrowsmith PN, Marks RG. Visual, refractive, and keratometric results of radial keratotomy: a two-year follow-up. Arch Ophthalmol. 1987;105:76-80.

2. SaIz JJ. Radial keratotomy. In: Thompson FB, ed. Myopia Surgery: Anterior and Posterior Segments. New York, NY: Macmillan Publishing, Ine; 1990:31-65.

3. Swinger CA. Variables in radial keratotomy. In: Cornea, Refractive Surgery, and Contact Lens. Transactions of the New Orleans Academy of Ophthalmology. New York, NY: Raven Press; 1987:89-110.

4: Hanna KD, Jouve FE, Waring GO III. Preliminary computer simulation of the effects of radial keratotomy. Arch Ophthalmol. 1989;107:911-918.

5. Waring GO III, Lynn MJ, Fielding B, the PERK Study Group. Results of the Prospective Evaluation of Radial Keratotomy (PERK) study 4 years after surgery for myopia. JAMA. 1990;263:1083-1091.

6. Thornton SP. One- vs two-stage procedure (response). J Refract Corneal Surg. 1989;5:125

7. Crabb JL. One- vs two-stage procedure (letter). J Refract Corneal Surg. 1989;5:125.

8. Lynn MJ, Waring GO III, Nizam A, the PERK Study Group. Symmetry of refractive and visual acuity outcome in the Prospective Evaluation of Radial Keratotomy (PERK) study. J Refract Corneal Surg. 1989;5:75-81.

9. Szerenyi K, McDonnell JM, Smith RE, Irvine JA, McDonnell PJ. Keratitis as a complication of bilateral, simultaneous radial keratotomy, Am J Ophthalmol. 1994;117:462-467.

Table 1

Data on Two Groups of Patients Receiving Bilateral Radial Keratotomy (RK)

Table 2

Pre- and Postoperative Refractive Errors (D, Mean ± SD) in Two Groups of Patients Receiving Bilateral Radial Keratotomy (RK)

Table 3

Postoperative Difference in Refractive Error (D) Between Right and Left Eye*

Table 4

Percentage of Overcorrections

10.3928/1081-597X-19940901-12

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