Journal of Refractive Surgery

The articles prior to January 2013 are part of the back file collection and are not available with a current paid subscription. To access the article, you may purchase it or purchase the complete back file collection here

Original Articles 

Regression of Effect Following Radial Thermokeratoplasty in Humans

Sandy T Feldman, MD; William Ellis, MD; Joseph Frucht-Pery, MD; Arturo Chayet, MD; Stuart I Brown, MD

Abstract

ABSTRACT: Radial thermokeratoplasty is a new refractive surgical technique designed to reduce hyperopia and/or astigmatism. Four patients underwent this surgery between February and March 1988 and were monitored postoperatively for the refractive effect and evidence of endothelial cell damage. Immediately following surgery, all eyes were overcorrected, but with time regression of the effect occurred. By 10 to 12 months postoperatively, only 18% of the desired effect remained. No decrease in the central endothelial cell density occurred during this time. Further investigation into the predictability and stability of results is needed to evaluate the longterm effectiveness of this technique. [Refractive and Corneal Surgery. 1989; 5:288-291].

Abstract

ABSTRACT: Radial thermokeratoplasty is a new refractive surgical technique designed to reduce hyperopia and/or astigmatism. Four patients underwent this surgery between February and March 1988 and were monitored postoperatively for the refractive effect and evidence of endothelial cell damage. Immediately following surgery, all eyes were overcorrected, but with time regression of the effect occurred. By 10 to 12 months postoperatively, only 18% of the desired effect remained. No decrease in the central endothelial cell density occurred during this time. Further investigation into the predictability and stability of results is needed to evaluate the longterm effectiveness of this technique. [Refractive and Corneal Surgery. 1989; 5:288-291].

Radial thermokeratoplasty is a new surgical technique designed by Fyodorov to reduce hyperopia and astigmatism. The efficacy of this technique has not yet been established. The purpose of this study is to report the results of four cases with follow-up between nine and 12 months.

SUBJECTS AND METHODS

Four eyes of four patients underwent radial thermokeratoplasty for hyperopia with or without astigmatism by one surgeon (WE), under Food and Drug Administration/Investigational Device FDA/IDE No. G880151. Informed consent was obtained after the nature of the procedure was explained carefully and under supervision of the internal review committee of the Eye Center of Northern California. Preoperative examination included visual acuity, manifest and cycloplegic refraction, keratometry, gonioscopy, corneal diameter, corneal rigidity, biomicroscopy of the cornea and anterior chamber, intraocular pressure, and retinal examination. Patients were excluded from surgery if their angles were deemed closeable. The surgical procedure was determined according to the Fyodorov computerized program which utilized corneal thickness, diameter, rigidity, keratometry, anterior chamber depth, axial length, intraocular pressure, and refraction in its calculations.

Topical anesthesia was applied. The corneal thickness was determined by ultrasonic pachymetry. After calibration against a block type gauge, the guarded thermal probe was adjusted to 110% of the central thickness. The visual axis, optical and radial zones were marked and burns were produced by automatically inserting the preset wire probe into the cornea for 0.3 seconds. The wire probe was heated to a temperature of 600° C by the Fyodorov thermal unit. The surgical instrumentation and methodology were previously reported by Caster.1 Three to four burns depending upon the amount of hyperopia, were placed along each of the radial zones. If astigmatism was present, additional rays were added at the flat meridian or an elliptical optical zone was utilized. The surgical procedure for each case is shown in !able 1. At the end of surgery, topical gentamicin (Garamycin) was applied, a collagen shield was placed, and the eye was patched.

The clinical characteristics for the four patients are summarized in Tables 1 to 3. All patients were scheduled for daily follow-up examinations until epithelialization occurred and then at 2 weeks, 1, 3, 6, 9 and 12 months. An independent observer performed refractions, ultrasonic pachometry (Technar Pachysonic II), and endothelial cell counts (Bioptics, LSM 2000 Variable Frame Cell Count).

Table

TABLE 1Operative Data Radial ThermokeratoplastyTABLE 2Preoperative and Postoperative Measurements in OU Eyes Receiving Radial Thermokeratopiasty

TABLE 1

Operative Data Radial Thermokeratoplasty

TABLE 2

Preoperative and Postoperative Measurements in OU Eyes Receiving Radial Thermokeratopiasty

Statistical analysis was performed with the Statview 512+ program (Calabasas, Calif) on a Macintosh SE computer. Two tailed, paired t-tests were used to compare preoperative and postoperative values. A P value of < 0.05 was considered significant.

RESULTS

The surgical procedure was performed without difficulty in three eyes. However, during surgery on the fourth eye (case two), the automated wire probe failed to retract after the fourth burn. The procedure was terminated and completed four days later after repair of the thermal unit.

Immediately after surgery, slit-lamp biomicroscopy revealed that all corneas were clear centrally and between the coagulation sites (Figure 1). With time, the scars became less dense but larger than the initial burns. Epithelial inclusion cysts, iron lines, variability of depth, and corneal neovascularization of peripheral burns were other observed changes. Corneal scarring varied among the patients (Figure 2).

The results of surgery for the four patients are shown in Tables 2 and 3. The average mean preoperative refraction was +3.91 ± .51 diopters while the mean postoperative spherical equivalent manifest refraction at 1 month was - 1.94 ± 1.14 D (range -3.63 to -1.13 D), at 3 months was +0.07 ±.90 D (range -0.75 to +1.25 diopters) at 6 months was +1.21 ± 0.81 D±D(range+0.37to+2.00D),and at 9 months was +1.94 ± 0.73 D (range +1.37 to +3.00 D). The mean preoperative average central keratometric power was 44.42 ± 1.63 D (3 eyes) while the mean postoperative measurement at last follow-up (9 to 12 months) was 46.02 ± 1.05 D. The effect regressed with time in all eyes (Figure 3). The mean central corneal thickness was .506 ± .017 mm preoperatively and .502 ±.023 mm postoperatively (P > .05). Measurements of the central cornea] thickness of both eyes in case 2 may have been inaccurate preoperatively or postoperatively. The mean endothelial cell counts were not significantly reduced and hexagonal morphology was preserved. In case 4, polymegathism was noted centrally in both the operated and unoperated eyes postoperatively. This patient was refitted with a contact lens in the operated eye 8 months after surgery and also wore a contact lens in the contralateral eye.

Table

TABLE 3Central Corneal Thickness and Endothelial Cell Counts Before and After Radial ThermokeratoplastyFigure 1: Slit-lamp photograph of an eye immediately following radial thermokeratoplasty. The cornea is clear between the opacities of coagulation.Figure 2: Slit-lamp photograph of an eye (case 1) 1 year following radial thermokeratoplasty. The cornea is clear between the opacities.

TABLE 3

Central Corneal Thickness and Endothelial Cell Counts Before and After Radial Thermokeratoplasty

Figure 1: Slit-lamp photograph of an eye immediately following radial thermokeratoplasty. The cornea is clear between the opacities of coagulation.

Figure 2: Slit-lamp photograph of an eye (case 1) 1 year following radial thermokeratoplasty. The cornea is clear between the opacities.

DISCUSSION

Thermal remodeling of corneal shape has been reported for almost 100 years.2 The rationale for utilizing heat to reshape the cornea stems from the fact that corneal collagen shrinks at temperatures of 55 to 600C3. In the earlier studies, the delivery of heat to the corneal surface was accomplished through hand held cauteries,24 surface heating probes,5 radiofrequency waves,6 and heated brass rings.7 Recently, Fyodorov has designed a new instrument capable of producing intrastromal burns to 6000C within a desired corneal depth to produce collagen shrinkage and thereby steepen the central cornea. Three to four burns are placed along each of 6 to 12 radiais to reduce hyperopia. This report describes the results of four early cases of radial thermokeratoplasty for hyperopia correction.

Figure 3: Change in spherical equivalent (manifest refraction) compared to time after radial thermokeratoplasty in four eyes. There is a gradual loss of effect in all eyes during the 4-year postoperative period. (LD = case1.PS= case 2, JM = case 3, VG = case 4).

Figure 3: Change in spherical equivalent (manifest refraction) compared to time after radial thermokeratoplasty in four eyes. There is a gradual loss of effect in all eyes during the 4-year postoperative period. (LD = case1.PS= case 2, JM = case 3, VG = case 4).

Four patients who underwent unilateral radial thermokeratoplasty were followed for almost 1 year. Radial thermokeratoplasty initially reduced hyperopia; however the effect was not stable. AU eyes achieved their refraction closest to emmetropia at the 3-month visit but there was a progressive decrease in effect throughout the observed postoperative period. No patient achieved a stable refraction by 9 months (Figure 3). Fyodorov has also noted regression in some eyes with fading of scars (unpublished communication). He advised against performing surgery in the second eye in such patients. De novo production of collagen by fibroblasts may be responsible for the regression of effect, although the exact cause is unknown.

The surgical complications were few. One operation was interrupted by loose wiring in the foot pedal control responsible for retraction of the automated probe. Burns were sometimes irregularly placed along the pre-marked radial zones since the thin wire probe bent easily. Also, burns were not uniform in size or depth and were occasionally placed closer than desired to each other and to the limbus. Technical advances in instrumentation and experience with the surgical technique may overcome these problems

These patients experienced a moderate amount of discomfort for 24 to 72 hours postoperatively. Epithelial healing occurred within 72 hours in all patients. Filaments were noted in case 4 at the 2week visit and epithelial plugs were noted in case 3. Recurrent erosions and persistent epithelial defects were not observed. As expected, neovascularization occurred at burn sites placed near the limbus. Peripheral burns induced by cautery in rabbit corneas have been shown to cause increased polymorphonuclear leukocyte infiltration and neovascularization whereas central burns do not cause neovascular ingrowth.8 With time, the initial opacification was less but the area was somewhat enlarged. Burns too close to each other resulted in confluency. Fibroblastic invasion and deposition of new collagen beneath and surrounding the scar may have been responsible for the fading and spreading observed.

The results of this limited study suggest that the stability of radial thermokeratoplasty is not reached almost 1 year after surgery and that only low amounts of hyperopia may be corrected. The predictability in all four individuals fell short of that desired for refractive surgical procedures. Prior studies utilizing heat to modify corneal shape have also failed to show a predictable and stable result.4,7,10,12 Additional investigation is necessary to establish the long-term effectiveness of this procedure.

REFERENCES

1. Caster AI. The Fyodorov technique of hyperopia correction by thermal coagulation: A preliminary report. Journal of Refractive Surgery. 1988; 105-108.

2. Lans LJ. Experimentelle untersuchunger über die entstehung von astigmatismus duch nicht-perforirende corneawunden. Albrecht von Graefes Arch Klin Exp Ophthalmol. 1898; 45:117-152.

3. Stringer EH, Parr J. Shrinkage temperature of eve collagen. Nature. 1964; 203:107.

4. O'Connor R. Corneal cautery for high myopic astigmatism. Am J Ophthalmol. 1933; 16:337.

5. Gassett AR, Shaw EL, Kaufman HE, et al. Thermokeratoplasty. Trans Am Acad Ophthalmol Otolaryngol. 1973; 77:441-454.

6. Rowsey JJ, Doss JD. Preliminary report of Los Alamos keratoplasty techniques. Ophthalmology. 1981; 88:755-760.

7. Gruenberg P, Manning S, Miller D, et al. Increase in rabbit corneal curvature by heated ring application. Ann Ophthalmol. 1981; 13:67-70.

8. Schanzlin DJ, Cyr RJ, Friedlander MD. Histopathology of corneal neovascularization. Arch Ophthalmol. 1983; 101:472-474.

9. Shaw E. Collagen shrinkage procedures for keratoconus and corneal astigmatism. Int Ophthalmol Clin. 1983; 23:127-135.

10. Rowsey JJ. Electrosurgical keratoplasty: update and retraction. Invest Ophthalmol VTs Set. 1987; 28:224.

TABLE 1

Operative Data Radial Thermokeratoplasty

TABLE 2

Preoperative and Postoperative Measurements in OU Eyes Receiving Radial Thermokeratopiasty

TABLE 3

Central Corneal Thickness and Endothelial Cell Counts Before and After Radial Thermokeratoplasty

Figure 1: Slit-lamp photograph of an eye immediately following radial thermokeratoplasty. The cornea is clear between the opacities of coagulation.

Figure 2: Slit-lamp photograph of an eye (case 1) 1 year following radial thermokeratoplasty. The cornea is clear between the opacities.

10.3928/1081-597X-19890901-04

Sign up to receive

Journal E-contents