Radial keratotomy for residual myopia after photorefractive keratectomy

Marvin L. Kwitko, MD, Sayed Jovkar, MD, Hua Yan, MD, Moustafa Atas, MD

ABSTRACT

Purpose: To evaluate the safety, efficacy. and complications of radial keratotomy (RK) after photorefractive keratectomy (PRK) for myopia.

Setting: Laser Ultravision Institute. Montreal. Canada.

Methods: Surgically induced refractive and visual acuity changes were retrospec­tively evaluated in 14 eyes of 10 patients treated with RK after PRK. All patients had simple myopia or compound myopic astigmatism. Minimum follow-up was 6 months.

Results: Three eyes (21 %) had one PRK. 7 (50%) had two treatments, and 4 (29%) had three. Eleven eyes (79%) required four-incision RK and 3 (21%), eight-incision RK. All patients had improved uncorrected visual acuity. Six months after the RK re­treatment. there was a significant reduction in spherical equivalent of 2.93 diop-ters :!: 1.53 (SO) (P < .05). No intraoperative or postoperative complications occurred except overcorrection (two cases).

Conclusion: Radial keratotomy is an effective, safe method for treating undercorrected myopia after PRK. Further study and analysis of this series of patients are planned. J Cataract Refract Surg 1998; 24:315-319

P hotorefractive keratectomy (PRK) can ablate mi­

croscopic layers of tissue to reduce the curvature of

the cornea. I- 3 Radial keratotomy (RK) involves making

radial incisions in the cornea with a calibrated diamond

knife. The incisions weaken the peripheral cornea,4

which then moves anteriorly under the influence of

intraocular pressure (lOP), causing a compensatory

posterior movement and flattening of the central cornea.

From the Department of Ophthalmology, McGill University, and St. Mary's Hospital and Jewish General Hospital, Montreal, Quebec, Canada (Kwitko, Jovkar), Department of Ophthalmology, Tianjin Medical University Hospital, People's Republic of China (Yan), and Department of Ophthalmology, University of Firat, Eiazig, Turkey (Atas).

The side effects of excimer laser refractive surgery include corneal haze, irregular astigmatism, decentration,

undercorrection or overcorrection, delayed epithelial

healing, contact lens intolerance, and visual symptoms

such as halos, glare, and monocular diplopia. 5.6 Al­

though excimer laser PRK is effective, predictable, and

safe in treating myopia/-9 undercorrections can persist

in some highly myopic eyes, even after one or more

repeated procedures. These undercorrections are the

result of the technique's limitations and the unique

tissue response of each eye.10-14 The residual refraction

treated initially by PRK can be corrected by PRK or RK

in some patients.

Reprint requests to Marvin L. Kwitko, MD, 5591 Cote des Neiges, Montreal, Quebec H3 T 1 Y8, Canada.

Several studies have reported PRK re-treatment for

undercorrection resulting from the initial PRK treat­

ment. 10-

14 However, to our knowledge, the re-treatment

J CATARACT REFRACT SURG-VOL 24, MARCH 1998 315

RK AFTER PRK FOR UNDERCORRECTION

of undercorrection by RK has not been reported. This Table 1. Nomogram for four-incision RK.

study assessed the safety, efficacy, and complications of RK to correct residual myopia after PRK.

Patients and Methods

This retrospective study analyzed the results of RK to treat undercorrected myopia after PRK in 14 eyes of 10 patients. Inclusion criteria for the initial PRK treatment were contact lens intolerance, dissatisfaction with spectacle correction, 21 years or older, stable myopia, and best corrected visual acuity (BCVA) of 20/40 or better. Exclusion criteria included previous corneal disease, uveitis, glaucoma, collagen vascular disease, and use of systemic corticosteroids. The inclu­sion criteria for RK after PRK were a refractive power greater than 1.50 diopters (D), persistent myopia after multiple previous PRK treatments, or patient request.

Preoperative examinations included manifest and cycloplegic refractions, slitlamp biomicroscopy, ultra­sonic pachymetry, corneal sensitivity (Cochet-Bonnet anesthesiometer), keratometry, videokeratography (Eye­Sys) , and measurements of Snellen visual acuity, pupil size in dim and normal light, and lOP.

PRJ( Protocol

The patient was placed in a supine position be­neath the operating microscope delivery system of the ExciMed UV200LA (Summit Technology) or Technolas Keracor 116 (Chi ron Vision Corp.) excimer laser. A drop of proparacaine 0.5% was applied to the eye as a topical anesthetic and a lid speculum used to expose the cornea. The corneal epithelium was then removed by mechanical scraping with a blunt spatula for an optical zone of 7.0 mm. With the patient fixating on the fixation light, corneal ablation was performed. At the

end of the procedure, a contact lens was placed and a drop of diclofenac sodium (Voltaren®) and oxyfloxacin (Ocuflox®) were instilled in the eye.

Patients were followed daily until complete re­

epithelialization. The contact lens was then removed, and fluorometholone (FML Forte®) drops were in­stilled four times daily for 1 month and then tapered to three times daily for 2 months. Follow-up examinations were performed at 1, 2, 3, and 6 weeks and 3 and 6 months.

Optical ZOne (mm)

ComIctIon (0) Age 20 Age 30 Age 40 Age &0, Age 60

1.50 4.00 4.50 4.75 5.00 5.50

2.00 3.50 4.00 4.50 4.75 5.25

2.25 3.25 3.50 4.00 4.25 4.75

2.50 3.25 3.50 4.00 4.25 4.75

2.75 3.00 3.25 3.75 4.00 4.50

3.00 3.00 3.25 3.75 4.00 4.50

3.50 3.50 3.75 4.25

4.00 3.00 3.50 4.00

4.50 3.25 3.75

5.00 3.00 3.50

6.00 3.00

Note: Age given in years

RJ( Protocol Corneal anesthesia was achieved with proparacaine

hydrochloride 0.5%. With the patient fixating on the operating microscope light, the center of the pupil was marked. The diamond knife was calibrated with a microscope. The blade was set at 110% of the thinnest eight paracentral intraoperative pachymetry measure­ments 1.5 mm from the optical center.

A back-cutting knife was set into the cornea at the optical zone and with steady guidance, an incision made to the limbus (one pass). The nomograms used are shown in Tables 1 and 2. At the end of the procedure, topical antibiotic drops were instilled on the cornea and an eyepatch was applied. Patients were examined at 1 day and 1 week, during which they took antibiotics, and at 1 month postoperatively. After re­epithelialization, fluorometholone 0.1 % was instilled four times daily for 1 month and then tapered to three times daily for another month.

Results Minimum follow-up for all patients was 6 months.

Age of the 5 men and 5 women ranged from 26 to 68 years. The mean interval between PRK re-treat­ments was about 3.25 months (range 3 to 4 months) and between PRK and RK re-treatment, about 20 months (range 4 to 27 months). Three eyes (21 %) had one PRK, 7 (50%) had a second PRK, and 4 (29%) had a third PRK. Of the 14 treated eyes,

316 J CATARACT REFRACT SURG-VOL 24, MARCH 1998

RK AFTER PRK FOR UNDERCORRECTION

Table 2. Nomogram for eight-incision RK.

Optical Zone (mm) (WomanlMan)

Correction (D) Age 20 Age 30 Age 40 Age 50 Age 60

1.50* 4.75/5.00 5.00 5.25 5.50 5.75

2.00* 4.50/4.75 4.75/5.00 5.50 5.25 5.75

2.50* 4.25/5.00 4.50/4.75 4.75 5.00 5.50

3.00* 400/4.25 4.25/4.50 4.75 5.00 5.25

3.50* 3.75/4.00 4.00 4.25 4.75 5.00

4.00* 3.50/3.75 3.75 4.00 4.50 4.75

4.50* 3.25/3.50 3.50 3.75 4.25 4.50

5.00 3.00/3.25 3.25 3.50 4.00 4.25

5.50 3.00 3.25 3.25 3.75 4.00

6.00 3.00 3.00 3.00 3.50 3.75

7.00 3.25 3.50

8.00 3.00 3.25

Note: Age given in years. If one value is given for optical zone size, it applies to both men and women. *Consider using a smaller optical zone and four-incision RK if recommended optical zone is larger than 4.0 mm

11 (79%) received four-incision RK and 3 (21%), eight-incision RK.

Visual Acuity Uncorrected visual acuity (UCVA) ranged from

20/300 to 20/400 preoperatively, 20/60 to 20/400 after PRK, and 20/20 to 20/80 6 months after RK. All patients had an improved UCVA after the RK re­treatment. Nine patients (64%) had a UCVA of 20/40 or better.

Refraction Table 3 shows refraction over time. Preoperative

and postoperative refractions were manifest refractions. When the astigmatism was 0.750 or less, the spherical equivalent was used. In eyes with the RK treatment after PRK, the mean spherical equivalent was -7.95 0 ± 2.92 (SO) before PRK, - 3.50 ± 1.56 0 after PRK, and -0.61 ± 1.14 0 6 months after RK (Figure 1). There was a significant reduction in spherical equiva­lent of 2.93 ± 1.53 0 6 months after RK (P < .05).

Overcorrection Overcorrection was defined as a change in spherical

equivalent in excess of the original refraction. Six months after RK, two eyes were overcorrected. In one,

with a pre-RK refraction of -5.00 0, the overcorrec­

tion was 1.75 O. In the other, with a pre-RK refraction of -2.50 0, the overcorrection was about 0.50 O. There were no other complications including corneal perforation, corneal edema, delayed epithelialization, and corneal ulcers.

The keratometry, computerized videokeratography, pupil measurements, and corneal sensitivity results will be published later.

PostRK 0

·2

rI.l a. -4 ~ ..... Q.

PreRK

I I

= -6 ... ~

-8

-10 -'--

Figure 1. (Kwitko) Change in spherical equivalent. The black squares denote the mean and the bars, the standard deviation.

J CATARACT REFRACT SURG-VOL 24, MARCH 1998 317

RK AFTER PRK FOR UNDERCORRECTION

Table 3. Summary of refractive data.

Pa· Age tlent Sex, f(em) 'Eye UCVA BCVA

Retrac­tfon (D)

RK

Clear zone fnd. (10m) sIons UCVA BCVA

ReI't'ac>, ,I!on(O}

RK-Induced RJfractive

" Change

M

2 M

3 F

4 M

5 F

6 F

7 F

54

26

34

51

30

41

42

L 20/400 20/50 -12.00 -1.25 x 170 3

R 20/400 20/20 -7.00

R 20/400 20/20 -4.50 2

L 20/400 20/20 -5.50 2

R 20/400 20/20 -5.50 -0.75 x 90 3

R 20/400 20/20 -6.00

L 20/400 20/20 -6.00

R 20/400 20/40 -10.25 -3.00 x 14 3

R 20/300 20/20 -5.25 2

20/300 20/50

20/80 20/20

20/80 20/20

20/100 20/20

20/60 20/20

20/80 20/20

20/100 20/20

20/400 20/40

20/100 20/20

-5.00

-1.75

-3.25

-4.00

-2.50

-2.00

-2.75

-5.00

-2.25

3.00

3.75

3.25

3.00

4.25

4.00

3.25

3.50

4.00

8

4

4

4

4

4

4

8

4

20/60 20/50

20/20 20/20

20/25 20/20

20/20 20/20

20/30 20/20

20/30 20/20

20/30 20/20

20/50 20/40

20/20 20/20

-1.25

o -0.75

-0.50

-100

-100

-0.75

+1.75

o

-3.75

-1.75

-2.50

-3.50

-150

-100

-2.00

-6.75

-2.25

L 20/300 20/20 - 5.25 2 20/100 20/20 -1.50 4.50 4 20/20 20/20 o -1.50

8 F 38 R 20/400 20/40 -9.25 -100 x 20 2 20/200 20/40 -4.50 4.00 4 20/50 20/40 plano -100 x 20 -4.50

L 20/400 20/40 -12.00 3 20/100 20/40 -2.50 4.00 4 20/40 20/40 +0.50 -3.00

9 M 59 L 20/400 20/40 -8.50 -0.50 x 180 2 20/200 20/40 -6.00 3.25 8 20/80 20/40 -3.25 - 2. 75

10 M 68 R 20/400 20/25 -11.00 2 20/300 20/25 -6.00 3.00 4 20/60 20/25 -175 -4.25

Note: The postoperative refractions are spherical equivalents. The complete refraction is listed only if astigmatism was 1.00 D or greater.

Discussion

Changing the shape of the cornea with the excimer laser is a more recently developed technique than RK. Photo refractive keratectomy is safe, predictable, and effective in treating myopia. However, undercorrection after PRK still occurs in eyes with high myopia because of individual corneal tissue response. 10-14

There are several approaches to treating under­correction after PRK. Snibson et al. 13 found that re­treatment with PRK appeared to enhance the results of previous PRK, although it was less successful than the initial procedure. In a study by Epstein and coauthors, 14

the majority of PRK regressions were successfully re­treated with PRK. Seiler and coauthors l5 reported that repeated photoablation seemed to be valuable for treat­

ing undercorrection after PRK. Another technique to treat undercorrection after

PRK is RK. We evaluated the safety of RK treatment

after PRK. There was no loss of BCVA, and all patients had improved UCVA. No intraoperative or postopera­tive complications occurred except overcorrection (two cases). Uncorrected visual acuity remained stable from 1 to 6 months after RK.

Table 4 compares our results using RK with previ­ous reports using PRK to re-treat residual myopia. The

Table 4. Summary of results of PRK and RK re-treatments for residual myopia after PRK.

Matta 'O 22

Sutton" 18

POp'2 56

Snibson '3 48

Epstein14

Present

17

14

Results at (Months)

12

6

12

12

6

6

UCVA = uncorrected visual acuity 'Only first author listed tOf intended correction

Percentage Of Patients

UCVA 20140 Within or Better :::!: 1.00 ot

77 82

50 50

76' 50'

64 69

65

64

59

71

'Authors divided patients into two subgroups: no haze and

previous haze; percentages represent the subgroup with previous haze

percentage of eyes achieving a UCVA of20/40 or better and of eyes within ± 1.00 D of intended correction were similar for both RK and PRK re-treatment. Thus,

both PRK and RK were effective in treating under­correction after PRK.

In our study, there was a significant reduction in mean spherical equivalent from post-PRK (-3.50 +

318 J CATARACT REFRACT SURG-VOL 24, MARCH 1998

RK AFTER PRK FOR UNDERCORRECTION

1.56 D) to post-RK (-0.61 ± 1.14 D). Although the

number of eyes and follow-up were limited, the treat­

ment of RK after PRK for residual myopia appears to

be effective. We will follow these patients and study the

long-term effects of RK for undercorrection after PRK.

References

1. Kim }H, Hahn TW, Lee YC, et al. Photorefractive keratectomy in 202 myopic eyes: one year results. Refract Corneal Surg 1993; 9(2 suppl):SII-SI6

2. Kwitko ML, Gow}, Bellavance F, Wu}. Excimer laser photo refractive keratectomy: one year follow-up. Oph­thalmic Surg Lasers 1996; 27(suppl):S454-S457

3. Seiler T, Wollensak}. Myopic photorefractive keratec­tomy with the excimer laser: one-year follow-up. Oph­thalmology 1991; 98:1156-1163

4. Rashid ER, Waring GO III. Complications of radial and transverse keratotomy. Surv Ophthalmol 1989; 34(2): 73-106

5. Seiler T, Holschbach A, Derse M, et al. Complications of myopic photo refractive keratectomy with the excimer laser. Ophthalmology 1994; 101: 153-160

6. Halliday BL. Refractive and visual results and patient satisfaction after excimer laser photorefractive keratec­tomy for myopia. Br} Ophthalmol 1995; 79:881-887

7. Wu HK, Demers PE. Photorefractive keratectomy for myopia. Ophthalmic Surg Lasers 1996; 27:29-44

8. Lee YC, Park CK, Sah WJ, et al. Photorefractive keratec­tomy for undercorrected myopia after radial keratot­omy: rwo-year follow up.} Refract Surg 1995; 11 (suppl): S274-S279

9. Kwitko ML, Gow}A, Bellavance F, Woo G. Excimer photo refractive keratectomy after undercorrected radial keratotomy. } Refract Surg 1995; 11 (suppl):S280-S283

10. Matta CS, Piebenga LW, Deitz MR, Tauber). Excimer retreatment for myopic photorefractive keratectomy fail­ures. Ophthalmology 1996; 103:444-451

11. Sutton G, Kalski RS, Lawless MA, et al. Excimer retreatment for scarring and regression after photore­fractive keratectomy for myopia. Br} Ophthalmol1995; 79:756-759

12. Pop M, Aras M. Photorefractive keratectomy retreatments for regression. Ophthalmology 1996; 103: 1979-1984

13. Snibson GR, McCarry CA, Aldred GF, et al. Retreatment after excimer laser photo refractive keratectomy. Am } Ophthalmol 1996; 121 :250-257

14. Epstein D, Tengroth B, Fagerholm P, Hamberg-Ny­strom H. Excimer retreatment of regression after photo­refractive keratectomy. Am } Ophthalmol 1994; 117: 456-461

15. Seiler T, Derse M, Pham T. Repreated excimer laser treatment after photorefractive keratectomy. Arch Oph­thalmoI1992; 110:1230-1233

J CATARACT REFRACT SURG---VOL 24. MARCH 1998 319