Radial keratotomy in perspective

Radial keratotomy is a surgical procedure to reduce or eliminate myopia. Advocates of radial keratotomy stress the dependence, inconvenience and restrictions of glasses or contact lenses. However, opponents of this procedure stress that invasive surgery on a healthy eye, regardless of the reason, is unethical. Candidates for radial keratotomy include adults with myopia between -2,00 and -8,00 diopters and who cannot tolerate contact lenses or glasses. The pre-operative evaluation and surgical techniques are briefly discussed. Complications of this procedure include sensitivity to glare, fluctuating vision, perforations, postoperative infections and corneal scarring. Overcorrections and undercorrections may also occur. It is shown that, although radial keratotomy is effective in the low-to-moderate myopia group, its effect in individual eyes is not totally predictable.     

Radial keratotomy in a patient with keratoconus

A 33-year-old patient had radial keratotomy performed on both eyes for relief of longstanding myopia. Minimal reduction of myopia was obtained, and the patient underwent a second radial keratotomy in both eyes. Best corrected visual acuity decreased, and the patient had a marked, irregular astigmatism postoperatively. Careful ophthalmologic evaluation revealed that the patient had keratoconus bilaterally. Following a failed trial of contact lens wear, the patient underwent a penetrating keratoplasty of the right eye. Pathologic evaluation revealed findings of keratoconus, as well as radial keratotomy scars. This case report illustrates the importance of a complete ophthalmologic examination possibly including videokeratography, prior to keratorefractive surgery.     

Radial keratotomy: prospective evaluation of safety and efficacy

One hundred five consecutive radial keratotomy procedures were followed for one year postoperatively. There was greatest correction of myopia with less than 8 diopters of preoperative correction, and correction to a lesser degree with more than 8 diopters of preoperative correction. There were no severe complications. Size of central optical zone, number of incisions, graduation of incisional depth, central corneal thickness, patient age, intraocular pressure, and sex are of value in predicting the success of the procedure.     

Radial keratotomy in myopia of 6 to 12 diopters using full-length deepening incisions

Radial Keratotomy was performed in 409 eyes with myopia of -6 to -12 diopters using eight incisions and deepening them from the optic zone to the limbus. The mean preoperative spherical equivalent refraction was -7.83 D and the mean postoperative was -1.02 D. Fifty-eight percent of the eyes were corrected to within 1 D of emmetropia and 38% achieved an uncorrected visual acuity of 20/40 or better.     

Ab interno radial keratotomy

We describe a modified approach to perform radial keratotomy which was tested in human donor eyes. Using a Beaver blade #5910, the sclera was entered tangentially 1 mm from the limbus up to the edge of the optical zone while staying in the deep stroma. The shaft was rotated 90 degrees, allowing the cutting edge to dissect from the deep stroma to the epithelium in a radial fashion. The procedure was repeated resulting in eight radial incisions. An average of 8.20 diopters (standard deviation SD = 2.40 D) of flattening was obtained in 20 human donor eyes. Histopathologic study of the radial incisions in another group of 10 donor eyes revealed a mean depth of 58.9% of corneal thickness. (SD = 12.4%). The present technique allows radial keratotomy to be performed without the sophisticated instrumentation necessary for the "external" approach.     

A comparison of one-stage radial keratotomy with two-stage radial keratotomy in myopia

To determine the efficacy of one-stage compared with two-stage radial keratotomy, a study was designed to compare both eyes of the same patient with moderate myopia; one eye was operated in one stage and the fellow eye in two stages. The surgical technique was identical in all four procedures of the two patients. Although the case for greater effectiveness with one-stage radial keratotomy cannot be proven on the basis of only a few cases, one-stage surgery appears to be more effective and more predictable.     

Five-year results of radial keratotomy

We present 5-year findings on 198 consecutive radial keratotomy surgeries. Follow-up was obtained on 134 (68%) of these eyes. Mean spherical equivalent (SE) was -4.3 diopters before surgery, average keratometry was 44.11 D, and 75% of eyes had uncorrected distance acuity of 20/400 or worse. Average SE was -0.52 D for eyes seen at 5 years, which compares with -0.78 D for eyes examined at 18 months. Seventeen percent of eyes show at least a 1-D change in refraction from 18 months to 5 years compared with 13% between 18 months and 3 years. Fifty-six percent of eyes are within 1 D of emmetropia at 5 years, compared with 66% at 18 months. Uncorrected visual acuity was at least 20/40 in 62% of eyes seen at 5 years and in 73% of eyes seen at 18 months. Ten percent of eyes have lost at least two lines of best-corrected visual acuity from before surgery to 5 years later. Factors are identified that relate to loss of uncorrected and best corrected acuity over 5 years. Average keratometry at 5 years is 40.7 D, as compared with 41.2 D at 18 months. Long-term keratometric results appear less stable than refractive results and a theory for this instability is presented. The results indicate radial keratotomy to be safe and effective for the vast majority of patients in this series for 5 years postoperatively.     

Hexagonal keratotomy for corneal steepening

Hexagonal keratotomy is evaluated for treatment of hyperopia, presbyopia, and radial keratotomy over-response. Initial indications are that this modality appears promising. Sixteen patients were evaluated and one complication is discussed.     

Factors that affect keratotomy depth

The authors investigated nine factors which can affect the depth of incisions performed during refractive keratotomy: (1) vertical vs oblique-cutting edge of the knife blade, (2) direction of cutting, (3) cutting velocity, (4) American vs Russian technique, (5) intraocular pressure (IOP), (6) initial vs final incisions, (7) sharpness of knife blade, (8) single vs double footplate, and (9) square vs double-edged blade. These variables were examined independently, performing at least 40 incisions for each experimental parameter studied. The depth of the resulting incisions was measured histologically using the micrometer eyepiece. The average and the standard deviation were calculated. The paired Student's t-test was used to establish significant differences between the two conditions investigated for each parameter. Factors that were demonstrated to increase significantly the depth of the incisions included: the vertical-cutting edge, the triple-edged diamond knife, the sharpness of the knife, and the single foot knife. High velocity in performing the incisions and, to a lesser extent, low IOP were the main factors that induced irregularity in depth.     

Learning curve for radial keratotomy

I prospectively evaluated my own learning curve for radial keratotomy (RK) by comparing the results achieved in two groups: 20 consecutive eyes on which I performed RK without having had previous experience with the procedure (group 1); and 20 other eyes, matched for age, sex, and preoperative refractive error, on which I performed RK after I had performed the procedure 250 times (group 2). Although there were nine microperforations in group 1 and none in group 2, the postoperative refractions and uncorrected visual acuities were similar in both groups. Since the microperforations had no adverse effect on the visual results, it is reasonable to conclude that there was, in effect, no learning curve involved in my experience with RK.     

Vacuum Fixation Ring for radial keratotomy

The Vacuum Fixation Ring helps stabilize the eye during radial keratotomy. It elevates the intraocular pressure, making the cornea rigid, and improves the control for deep reproducible incisions. The instrument is designed for use with topical anesthesia and a variety of diamond or steel knives.     

Relaxing keratotomy for post-keratoplasty high astigmatism

Seventeen patients underwent relaxing keratotomy for post-keratoplasty high astigmatism (range 8.5 to 18.0 diopters). The mean reduction in cylinder was 7.53 (+/- 3.13 SD) diopters, with a range from 2.5 to 11.5 diopters. There was a trend toward a more myopic spherical equivalent of 1.69 (+/- 2.29 SD) diopters with a range of 0.43 diopters of flattening to 5.5 diopters of steepening. Perforations occurred in two patients, but none had a permanent negative outcome.     

Inflammatory cell responses to radial keratotomy

Radial keratotomy stimulates the influx of polymorphonuclear cells (PMNs) into the tear film and stroma. These cells do not degranulate and are gone in four days. Incisions fill with persistent epithelial plugs, and extracellular matrix (ECM) replacement does not occur. In contrast, a thermal burn stimulates a prolonged influx of PMNs into the tear film and stroma, where they degranulate and remove damaged tissue. ECM replacement in a few weeks suggests that factors released by activated PMNs may stimulate normal wound healing in the cornea.     

Persistence of diurnal fluctuation after radial keratotomy

Three patients were examined before 8:00 AM and after 7:00 PM to determine diurnal changes in uncorrected visual acuity, refractive error, and average central keratometric power at 3 months, 4 years, and 6 years after radial keratotomy. The average absolute diurnal change in the spherical equivalent refraction increased over time: 0.26 diopters at 3 months, 0.75 D at 4 years, and 1.29 D at 6 years. Diurnal change in the absolute average keratometric values were not progressive: 0.35 D at 3 months, 0.27 D at 4 months, and 0.40 D at 6 years. Computer-assisted corneal topographic analysis demonstrated diurnal changes in the topography that may be subtle and not necessarily reflected in the average keratometry values. These limited data suggest that wound healing over several years may not restore stability to the cornea.     

Blindness following retrobulbar anesthesia for astigmatic keratotomy

Retrobulbar anesthesia has become the most common form of anesthesia used in ophthalmic surgery. Acute blindness is a rare but known complication of retrobulbar anesthesia given for intraocular surgery. I report a case of acute, permanent blindness caused by direct trauma to the optic nerve when retrobulbar anesthesia was used for an astigmatism correction procedure. Complications, sometimes probably too incidental or insignificant to be noticed, probably occur far more frequently than a review of the literature would indicate. Using dull shorter needles, proper eye positioning, and injection technique will minimize risk of injury to the optic nerve. Another alternative under review is the use of peribulbar anesthesia. Perhaps the best way to prevent a complication from a retrobulbar injection, however, is to carefully and judiciously consider whether any injection at all is needed.