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Photorefractive Keratectomy for Severe Postkeratoplasty Astigmatism
Photorefractive Keratectomy for Severe Postkeratoplasty Astigmatism Mauro C a m p o s , M.D., Lars Hertzog, B.S., Jenny Garbus, B.S., Martha Lee, P h . D . , and Peter J. M c D o n n e l l , M . D .
We performed cylindric corneal ablations with the excimer laser on 12 patients to correct severe, disabling astigmatism after keratoplasty. In some patients, an additional ablation was performed to correct myopia. Patients were followed up for an average of eight months (range, six to 14 months). Uncorrected visual acuity improved in nine patients, and nine of the 12 patients had a decrease in refractive cylinder at last follow-up. The mean preoperative refractive cylinder was 7.0 ± 3.6 diopters, which decreased to a mean of 3.1 ± 2.6 diopters at one month (P = .0003) and 4.3 ± 2.9 diopters at last follow-up (P = .03). Keratometric astigmatism decreased from 7.5 ± 3.9 diopters preoperatively to 5.2 ± 3.9 diopters at the last follow-up (P = .001). Mean spherical equivalent was reduced from - 7 . 4 ± 4.2 diopters preoperatively to —3.3 ± 4.4 diopters postoperatively (P = .003). Postoperative corneal haze, when present, did not reduce visual acuity. Excimer laser superficial keratectomy thus appears to be safe when used for postkeratoplasty ametropia, although substantial regression may limit its effectiveness in some patients. I HE OUTCOME of penetrating keratoplasty has improved with advances in microsurgical tech niques, more stringent criteria for selection of donor material, and better postoperative care. The visual recovery after such a surgical proce dure, however, is often adversely affected by
Accepted for publication June 26, 1992. From the Doheny Eye Institute, and Department of Ophthalmology, University of Southern California School of Medicine, Los Angeles, California. This study was supported by a grant from the Autry Foundation, Los Angeles, California (Dr. McDonnell). Reprint requests to Peter J. McDonnell, M.D., Doheny Eye Institute, 1450 San Pablo St., Los Angeles, CA 90033.
severe postoperative astigmatism despite a clear graft.1 Several surgical options have been described for correction of this postoperative astigmatism, but the results remain relatively unpredictable. 26 Photorefractive keratectomy with the 193-nm excimer laser is under investigation as an op tion for treatment of refractive errors and for excision of superficial cornea opacities. To cor rect myopia, a radially symmetric surgical pro cedure is performed with greater ablation depth centrally than peripherally 79 ; to excise superficial corneal opacities, a uniform ablation depth is used. 10 A nonradially symmetric ap proach to tissue ablation with flattening of the steep meridian for correction of corneal astig matism has been described in plastic spheres, animals, and human eyes.11·12 We used this tech nique for correction of severe astigmatism after keratoplasty.
Patients and Methods The laser used was a 193-nm argon-fluoride excimer laser (Twenty-Twenty, VISX, Inc., Sunnyvale, California). The detailed methods of this procedure have been described previous ly.1112 To correct astigmatism, a large-diameter laser beam is passed between a set of parallel blades. The separation between the blades is controlled by computer (with the slit opening during the procedure), and the resultant varia ble slit is used to control the laser delivery much as the iris diaphragm is used for correc tion of myopia. As in laser treatment to correct myopia, 240 steps are used. By using the slit, the resultant corneal flattening is only in the meridian perpendicular to the long axis of the slit (mechanical axis); no refractive change is intended along the mechanical axis. Alignment of the mechanical axis with the astigmatic axis of the patient is achieved by rotating the slit
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mechanism with computer control. Ablations were performed by using a fluence of 160 m j / cm2 and a repetition rate of 5 Hz. To calibrate the laser, we performed toric ablations in polymethylmethacrylate blocks and the induced cylinder was measured with a lensometer, as described previously. 11 Informed consent was obtained from all pa tients after the nature and risks of the proce dure were explained. To be eligible for the study, the patients must have had demonstrable improvement in visual acuity when corrected with the phoropter, but we did not require that they be correctable to 20/20. It was common for visual acuity to be correctable with contact lenses to a level one or two lines better than with spectacles, a consequence of a component of irregular astigmatism. Twelve patients were included in this study. None of these patients could tolerate contact lenses or the high cylindric correction needed in spectacles. Other sur gical options were offered to the patients. This investigational procedure is under a protocol approved by the Food and Drug Administration and the Institutional Review Board of the Uni versity of Southern California. Preoperative ex aminations included slit-lamp microscopy and photography for documentation. An experi enced examiner performed refraction, keratom etry, ultrasonic pachymetry, and computer-as sisted corneal topography preoperatively and postoperatively. The potential visual acuity was tested by contact-lens overrefraction or the Potential Acuity Meter if necessary (PAM, Men tor O & O Inc., Norwell, Massachusetts). Cor neal haze was graded preoperatively and post operatively as 0 (none), 0.5 (barely detectable), 1 (easily detectable, but not affecting refraction or retinoscopy), 2 (easily detectable and inter fering with retinoscopy and refraction), and 3 (obscuring iris details). The patients were then placed under the excimer laser, topical proparacaine hydrochloride was applied, and a circular protractor was placed on the globe at the corneoscleral limbus and oriented by using a landmark observed at the slit lamp preoperatively. A few pulses were then applied with the slit maximally narrowed to ensure proper orientation of the slit relative to the corneal cylinder and to acquaint the patient with the sensations associated with la ser ablation. The corneal epithelium was then removed with a blunt spatula, after which the eye was fixed by using a vacuum fixation ring, and the area of treatment centered over the entrance pupil, while the patient fixated on a
flashing centration light. The computer was programmed to perform cylindric ablations greater than or equal to 80% of the preoperative cylindric error, adjusted to the corneal plane. In one patient with postkeratoplasty astigmatism that measured 12 diopters, we programmed 50% correction and in two other patients a 66% correction was attempted. The desired refrac tive change was programmed into the computer in minus cylinder form (for example, piano - 6 . 0 0 x 180 designed to induce 6 diopters of flattening in the vertical meridian). The blades are oriented by the computer to be parallel to the axis of refractive cylinder expressed in mi nus cylinder form, thereby flattening the cornea in the appropriate (steeper) meridian. Patients were treated postoperatively with a combination tobramycin sulfate (0.3%)/dexamethasone sodium phosphate (0.1%) ointment and semipressure patching, and were examined daily or every other day until reepithelialization was complete. They were then treated with 1% prednisone acetate four times daily for two weeks, three times daily for four weeks, and twice daily for four more weeks. Two weeks and one, two, three, four, and six months postoper atively, refraction, keratometry, ultrasonic pachymetry, and computer-assisted topogra phy were performed by the same masked ob server. A paired two-tailed f-test was used to compare preoperative and postoperative meas urements. Data were computed as mean ± standard deviation.
Results Patients—We performed superficial toric ab lations with the excimer laser on 12 patients who had disabling postkeratoplasty astigma tism that had persisted for more than one year after removal of all corneal sutures. All patients were contact-lens intolerant and were unable to tolerate the high cylindric prescription in their spectacles. Prekeratoplasty diagnoses were keratoconus (Patients 3 through 6, 8, 9, 11, and 12), herpes (Patient 1), Fuchs' dystrophy (Pa tient 7), corneal scar (Patient 10), and chemical burn (Patient 2). Preoperative measurements disclosed that all patients except one (Patient 2) had potential visual acuity of 20/20. Patient 2, with a history of posttraumatic endophthalmitis, had a preoperative potential visual acuity of 20/60 as determined by the Potential Acuity Meter. Preoperative and postoperative refrac-
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TABLE 1 PATIENT DATA* PREOPERATIVE
POSTOPERATIVE
VISUAL ACUITY
PATIENT NO.,
VISUAL ACUITY
GENDER,
REFRACTION
WITH CORRECTION
DESIRED CORRECTION
WITHOUT
WITH
(DIOPTERS)
WITHOUT CORRECTION
REFRACTION
AGE (YRS)
(DIOPTERS)
CORRECTION
CORRECTION
TIME (MOS)
1,M, 76 2, M, 37 3, M, 72 4, F, 27 5, F, 52 6, M, 44 7, F.83 8, M, 63 9, F, 29 10, F, 80 11,M, 46 12, M, 36
+3.50 -12.00 x 5 -0.75 -6,00 x 135 -6.50 -2.25 x 42 -3.00 -5.00 x 157 -9.25 -4.00 x 55 -4.00 -5.00 x 106 -1.00 -6.00 x 170 -5.00 -14.00 x 133 -13.25 -6.25 x 55 -6.50 -8.50 x 42 -2.75 -3.75 x 29 +2.50-11.00 x 135
3/200 20/400 20/400 20/100 20/400 20/200 20/300 20/400 10/400 5/200 10/200 20/400
20/40 20/100 20/30 20/30 20/30 20/30 20/30 20/100 20/20 20/30 20/25 20/20
Piano -6.00 Piano -10.00 -3.00 -2.25 Piano -4.75 -8.5 -3.75 Piano -4.75 -2.00 -4.00 -6.00 -12.00 -11.50-4.00 -2.75 -6.75 -1.75 -3.75 -10.00
Piano -8.00 x 178 Piano -2.75 x 18 -5.00 -2.75 x 25 +2.50 -0.50 x 6 -1.50 -6.00 x 33 + 1.50-10.50 x 113 -0.50+1.00 x 180 + 12.50 -6.00 x 148 +5.00 -2.50 x 64 +0.50 -3.00 x 144 +0.50 -3.50 x 111 +3.50 -6.00 x 136
20/400 20/100 20/400 20/30 20/400 3/200 20/25 20/300 10/200 20/100 20/80 20/100
20/25 20/60 20/30 20/20 20/20 20/30 20/20 20/50 20/20 20/30 20/20 20/25
9 14 7 12 7 6 6 6 6 7 6 7
"Corrected visual acuity represents visual acuity with spectacles.
tive error, visual acuity, and keratometric measurements were determined (Tables 1 and 2). The patients were followed up for a mini mum of six months, and for a mean of eight months (range, six to 14 months). Visual acuity—Uncorrected visual acuity im proved by at least one Snellen line in nine of 12 patients (75%), decreased by one line in one patient, and did not change in two patients (Table 1). The visual acuity corrected with spec tacles improved in seven patients by at least one line, decreased in one patient, and was unchanged in four patients. The visual acuity of Patient 6, whose uncorrected visual acuity ( 3 / 200) was improved markedly with spectacles (20/30), had even greater improvement ( 2 0 / 25) with a gas-permeable contact lens. Refractive astigmatism—Photorefractive ker atectomy was performed on the basis of the total measured refractive cylinder corrected for the corneal plane in most of the patients. The attempted correction was plotted against the achieved correction (Rz = 0.40) (Fig. 1). Patient 1, who had 12 diopters of astigmatism preoperatively, had a target correction of 6 diopters of cylinder, and Patients 7 and 9 had corneal ablations calculated to correct 66% of the initial refractive cylinder. The mean changes in refrac tive cylinder were determined (Fig. 2). The mean preoperative refractive cylinder was 7.0 ± 3.6 diopters. One month postoperatively, a significant reduction in refractive cylinder was achieved (3.1 ± 0.7 diopters, P = .001). A slight
regression in the effect was first noticed two months postoperatively, and the average cor rection at most recent follow-up was 38%. The difference in the axis of refractive cylinder preoperatively and at the last follow-up disclosed a shift in the axis that ranged from 1 to 173 degrees, with a mean shift of 58 ± 62 degrees. Four patients (Patients 1, 2, 4, and 10) had overcorrection of their astigmatism, with a shift in the cylinder axis of more than 100 degrees. TABLE 2 KERATOMETRIC CYLINDER*
PATIENT
PREOPERATIVE
POSTOPERATIVE
NO.
DIOPTER
AXIS
DIOPTER
AXIS
1 2 3 4 5 6 7 8 9 10 11 12
17.38 5.50 3.12 4.37 6.50 7.63 4.38 12.37 6.36 8.37 5.38 8.75
95 53 3 75 150 16 82 41 174 175 115 45
13.75 1.88 3.60 3.17 6.50 6.25 1.87 10.50 2.50 4.00 0.60 8.70
87 109 110 78 142 19 108 43 154 38 108 58
'Mean (± standard deviation) preoperative keratometric cyl inder, 7.5 ± 4.0; mean (± standard deviation) postoperative keratometric cylinder, 5.2 ± 3.9 (P < .001).
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6-
Q
4"
y = 1.3568 + 0.67380X
R2
= 0.402 D
2-
oo •o
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Ηχ·*
-2^,— ^
-4-
a
a
a
--— o
-6" -8'
-16
I
-14
'
l
-12
—
1
'
1
-10
Attempted
-2 Weeks After
Correction
Surgery
Fig. 1 (Campos and associates). Attempted correc tion vs achieved correction after photorefractive ker atectomy for correction of postkeratoplasty astigma tism.
Fig. 2 (Campos and associates). Refractive cylinder (mean ± standard error) over time after photorefrac tive keratectomy for correction of postkeratoplasty astigmatism.
Excluding these four patients with overcorrected astigmatism, the change in refractive cylin der axis was 20.3 ± 25 degrees. Keratometric astigmatism—The average pre operative keratometric corneal cylinder was 7.5 ± 3.9 diopters (Table 2). Considering the kera tometric cylinder at the last follow-up of each patient, the average corneal cylinder was 5.2 ± 3.9 diopters (P = .001). Nine patients had a decrease in the corneal cylinder of at least 1.3 diopters, two patients did not have any change in keratometric cylinder, and the other patient showed an increase in corneal cylinder of 0.48
diopter, although the uncorrected visual acuity in this patient (Patient 3) did not change. The mean changes in the keratometric cylinder were determined (Fig. 3). The maximum decrease in the keratometric cylinder was noticed within three months postoperatively. Spherical equivalent—The mean preoperative spherical equivalent was - 7 . 4 ± 4.2 diopters. The mean changes in the spherical equivalent were determined (Fig. 4). Within the first eight weeks postoperatively, the mean spherical equivalent approached zero, and represented a
-6-*
Weeks After Surgery
Fig. 3 (Campos and associates). Keratometric cylin der (mean ± standard error) over time after photore fractive keratectomy for correction of postkeratoplas ty astigmatism.
Weeks After
Surgery
Fig. 4 (Campos and associates). Spherical equiva lent (mean ± standard error) over time after photore fractive keratectomy for correction of postkeratoplas ty astigmatism.
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hyperopic shift that persisted until 16 weeks (Fig. 4). A slight decrease in the surgical effect on the spherical equivalent was noticed after four months in most of the patients. At the six-month follow-up, Patient 3 had a substan tial regression of the surgical effect that had been present two months postoperatively (Fig. 5). Patient 4, with an intended cylindric correc tion of - 4 . 7 5 diopters, had a reduction in myopia from - 3 . 0 0 diopters preoperatively to - 1 . 0 0 diopters postoperatively (Fig. 6). Patient 6, with an intended correction of 5.00 diopters of cylinder, developed a hyperopic shift in the spherical error; at the last follow-up, mean spherical equivalent was —3.3 ± 4.4 diopters (P = .003). Pachymetry—The patients had a substantial decrease of the corneal thickness as an effect of excimer laser ablation. Two months postopera tively, the mean postoperative corneal thick ness increased temporarily (Fig. 7). At the last follow-up, the average corneal thickness was 0.46 ± 0.05 mm (P < .0001), with an average reduction of 0.09 ± 0.05 mm.
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Complications—In one patient (Patient 2), the epithelial defect had healed by 11 days postop eratively, whereas in all the other patients the defect healed within three days postoperative ly. Patieht 1 developed recurrent herpes sim plex epithelial keratitis four weeks after keratoplasty (successfully treated with topical trifluridine). Another recurrence in this patient ten months after photorefractive keratectomy resulted in graft failure caused by apparent subsequent immunologie rejection. Despite fre quent admonitions to report immediately any possible problems, this patient did not inform us in both instances of the decrease in vision and development of conjunctival injection for a week or longer after onset of symptoms, which delayed initiation of appropriate therapy. Oth er possible complications, such as corneal re jection, infection, or recurrent erosions, did not develop in our patients. Corneal haze—The amount of corneal haze was graded by one of us (P.J.M.) for all patients. All of the corneas were graded as clear (0) preoperatively. The amount of haze postopera-
Fig. 5 (Campos and associates). Color-coded keratograph of Patient 3 obtained before (top left), at one month (top right), and seven months postoperatively (bottom left). The central cornea is less astigmatic at one month, but substantial regression of the surgical effect is noted at seven months.
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Fig. 6 (Campos and associates). Color-coded keratograph of Patient 4 obtained preoperatively (left) and eight months postoperatively (right). An overall flattening of the cornea was achieved, with apparent inferotemporal decentration of the zone of flattening. tively ranged from 0.5 (barely detectable) to 1.0 (easily detectable, but apparently not interfer ing with retinoscopy or refraction). Pain—The amount of pain experienced by these postkeratoplasty patients was generally mild and much less intense than that experi enced by most patients we have treated with photorefractive keratectomy who have not had previous keratoplasty or other corneal surgical procedures.
Discussion Although several techniques for correction of severe astigmatism after keratoplasty have been described, the refractive outcomes of these pro cedures, and particularly the predictability, are still unsatisfactory. 261316 The limited surgical success is probably related to a poor under standing of the donor-host tissue relationship, which might be affected by such factors as faulty surgical technique (trephination and su ture placement) and postoperative care. At tempts to correct postkeratoplasty astigmatism with relaxing incisions and compression su tures have yielded fairly unpredictable re sults. 16 Our results in this initial group of pa tients, after a single superficial ablation with the excimer laser, are not demonstrably superi or to results of other small published surgical series in which incisions and compression su tures were used. Whether re-treating patients with undercorrected astigmatism will improve our overall results is unknown.
We wanted to evaluate the safety and efficacy of toric superficial corneal ablations for reduc ing postkeratoplasty astigmatism. Analysis of the corneal reepithelialization rate showed that the wound healing was not delayed in these postkeratoplasty patients when compared with the previously described reepithelialization rate in patients after photorefractive keratecto my for correction of myopia.17,18 The delayed reepithelialization (11 days) in one patient may have been a consequence of the corneal alkali burn for which the keratoplasty was performed, and of mildly decreased tear production (con firmed by a preoperative Schirmer test). The 0.60-1
?
0.55
«I
«M t
0.50
5
0.45
O
0.40 H
1
1
1
1
1
1
1
0
4
8
12
16
20
24
28
Weeks After
Surgery
Fig. 7 (Campos and associates). Corneal thickness (mean ± standard error) as measured with ultrasonic pachymeter over time after photorefractive keratec tomy for correction of postkeratoplasty astigmatism.
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amount of corneal haze in these patients was minimal and appeared not to affect the final vision. The absence of intraoperative complica tions and of postoperative corneal infections or graft rejections, and relatively minor pain ex perienced by these patients, suggest that this is a fairly safe surgical procedure. Other surgical techniques for correction of postkeratoplasty astigmatism have been associated with various intraoperative and postoperative complica tions; relaxing incisions have resulted in corne al abscesses19 and perforations,20 and allograft reactions have complicated wedge resections (Table 3).21 Uncorrected visual acuity improved in nine patients, but only two patients had uncorrected visual acuity of better than 20/40. All of our patients had best-corrected visual acuities of better than 20/60, which is comparable to pre vious results.1011 Nine of the 12 patients had a reduction in refractive cylinder to a level that was tolerable with spectacles. Disparity be tween refractive and keratometric cylinder and changes in each were common; Patient 6, for example, had a reduction of 1.4 diopters on keratometric cylinder, but an increase in refrac tive cylinder of 5.5 diopters. Other investiga tors82 have also demonstrated that refractive and keratometric cylinder may differ substan tially in postkeratoplasty patients. We observed a delayed loss of the initially achieved effect 12 weeks postoperatively (Fig. 5). It can be disappointing for patient and
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surgeon alike to observe an initially excellent optical result at one or two weeks postopera tively be lost as regression occurs. Other studies using the excimer laser for refractive surgical procedures have shown a regression of the initial effect also, usually within one to three months postoperatively.1718 We looked for a re lationship between changes in corneal thick ness over time and regression of refractive effect postoperatively, but no correlation could be demonstrated in our patients. Patients 6, 8, and 12, who had the most regression of refrac tive change, had a stable, unchanging corneal thickness postoperatively, even during and af ter the regression. Other studies using the excimer laser for photorefractive keratectomy for myopia have indicated better results in patients whose pre operative myopia was less than 5.00 diop ters.17·18 In our study, we did not observe a similar correlation between preoperative cylindric error and the accuracy of the surgical outcome. In five patients we noted a corneal flattening in excess of that predicted merely on the basis of flattening the steep meridian. The preopera tive flat meridian, in which a uniform depth of ablation is created, was also flattened (Fig. 6). As we have noted before,12 this extra effect will have to be considered when programming an astigmatic correction with the excimer laser. Surgical management of disabling astigma tism after keratoplasty is currently unsatisfac-
TABLE 3 PREVIOUS STUDIES OF SURGICAL TREATMENT FOR POSTPENETRATING KERATOPLASTY ASTIGMATISM COMPARED WITH OUR STUDY PROCEDURE STUDY (IN ORDER OF PUBLICATION)
NO. OF
USED TO PLAN SURGICAL TECHNIQUE
REDUCTION OF
(DIOPTERS)
PERIOD (MOS)
4 16 14 21
Arcuate keratotomy
Keratometry
75.0
8.40
Arcuate keratotomy
Keratometry
42.5
4.25
4 8.2
Arcuate keratotomy
Keratometry
60.0
7.50
Not available
Arcuate keratotomy and Keratometry compression sutures
67.0
6.56
6 to 9
McCartney and associates19
11
Relaxing incisions and compression sutures
Intraoperative keratoscopy
68.0
7.95
13.5
Cohen, Tripoli, and Noecker14
7 5
Arcuate keratotomy
Photokeratoscopy
69.8
6.52
7
Arcuate keratotomy or relaxing incisions
Photokeratoscopy
37.7
3.00
Not available
7
Relaxing incisions and compression sutures
Computer-assisted corneal topography
81.1
8.20
12.3
Photorefractive keratectomy
Refraction
38.0
2.30
7.7
Troutman and Swinger3 Krachmer and FenzP Sugar and Kirk13 Mandel, Shapiro, and Krachmer2'
Maguire and Bourne15 Frangieh, Kwitko, and McDonnell" Our study
CASES
12
SURGICAL TECHNIQUE
ASTIGMATISM (%)
KERATOMETRIC CYLINDER REDUCTION POSTOPERATIVE
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tory. O n the basis of o u r r e s u l t s , t h e u s e of t h e excimer laser to p e r f o r m toric a b l a t i o n s in p a t i e n t s w i t h severe a s t i g m a t i s m after k e r a t o p l a s ty a p p e a r e d to be safe, b u t the refractive r e s u l t s r e g r e s s e d s u b s t a n t i a l l y in s o m e p a t i e n t s , t y p i cally at a b o u t or after t h r e e m o n t h s . We h a v e yet to r e - t r e a t any p a t i e n t s w i t h u n d e r c o r r e c t e d astigmatism, and thus cannot comment on w h e t h e r a r e p e a t surgical p r o c e d u r e w o u l d yield b e t t e r r e s u l t s .
References 1. Swinger, C. A.: Postoperative astigmatism. Surv. Ophthalmol. 31:219, 1987. 2. Lavery, G. W., Lindstrom, R. L., Hofer, L. A., and Doughman, D. V.: The surgical management of corneal astigmatism after penetrating keratoplasty. Ophthalmic Surg. 16:165, 1985. 3. Troutman, R. C , and Swinger, C : Relaxing inci sion for control of postoperative astigmatism follow ing keratoplasty. Ophthalmic Surg. 11:117, 1980. 4. Lindstrom, R. L., and Lindquist, T. D.: Surgical correction of postoperative astigmatism. Cornea 7:138, 1988. 5. Villaseflor, R. A., and Stimac, G. R.: Clinical results and complications of trapezoidal keratotomy. J. Refract. Surg. 4:125, 1988. 6. Krachmer, J. N., and Fenzl, R. E.: Surgical cor rection of high postkeratoplasty astigmatism. Relax ing incision vs wedge resection. Arch. Ophthalmol. 98:1400, 1980. 7. Marshall, J., Trokel, S„ Rothery, S„ and Krueger, R. R.: Photoablative reprofiling of the cornea using an excimer laser. Photorefractive keratectomy. Laser Ophthalmol. 1:21, 1986. 8. Taylor, D. M., L'Espérance, F. A., Jr., Del Pero, R. A., Roberts, A. D., Gigstad, J. E., Klintworth, G., Martin, C. A., and Warner, J.: Human excimer laser lamellar keratectomy. A clinical study. Ophthalmolo gy 96:654, 1989. 9. McDonald, M. B., Frantz, J. M., Klyce, S. D„ Beuerman, R. W., Varnell, R., Munnerlyn, C. R., Clapham, T. N., Salmeron, B., and Kaufman, H. E.: Central photorefractive keratectomy for myopia. The blind eye study. Arch. Ophthalmol. 108:799, 1990. 10. Stark, W. J., Gilbert, M. L., Goodman, G. L., Gottsch, J. D., Trokel, S., and Munnerlyn, C : Phototherapeutic keratectomy preliminary report. ARVO
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abstracts. Supplement to Invest. Ophthalmol. Vis. Sci. Philadelphia, J. B. Lippincott, 1990, p. 245. 11. McDonnell, P. J., Moreira, H., Garbus, J., Clapham, T. N., D'Arcy, J., and Munnerlyn, C. R.: Photorefractive keratectomy to create toric ablations for correction of astigmatism. Arch. Ophthalmol. 109:710, 1991. 12. McDonnell, P. J., Moreira, H., Clapham, T. N., D'Arcy, J., and Munnerlyn, C. R.: Photorefractive keratectomy for astigmatism. Initial clinical results. Arch. Ophthalmol. 109:1370, 1991. 13. Sugar, J., and Kirk, A. K.: Relaxing keratotomy for post-keratoplasty high astigmatism. Ophthalmic Surg. 14:156, 1983. 14. Cohen, K. L., Tripoli, N. K., and Noecker, R. J.: Prospective analysis of photokeratoscopy for arcuate keratotomy to reduce postkeratoplasty astigmatism. Refract. Corneal Surg. 5:388, 1989. 15. Maguire, L. J., and Bourne, W. M.: Corneal topography of transverse keratotomies for astigma tism after penetrating keratoplasty. Am. J. Ophthal mol. 107:323, 1989. 16. Frangieh, G. T., Kwitko, S., and McDonnell, P. J.: Prospective corneal topographic analysis in surgery for postkeratoplasty astigmatism. Arch. Ophthalmol. 109:506, 1991. 17. Seiler, T., Kahle, G., and Kriegerowski, M.: Excimer laser (193nm) myopie keratomileusis in sighted and blind human eyes. Refract. Corneal Surg. 6:165, 1990. 18. McDonald, M. B., Liu, J. C , Byrd, T. J., Abdelmegeed, M., Andrade, H. A., Klyce, S. D., Varnell, R., Munnerlyn, C. R., Clapham, T. N., and Kaufman, H.: Central photorefractive keratectomy for myopia. Partially sighted and normally sighted eyes. Oph thalmology 98:1327, 1991. 19. McCartney, D. L., Whitney, C. E., Stark, W. J., Wong, S. K., and Bernitsky, D. A.: Refractive kerato plasty for disabling astigmatism after penetrating keratoplasty. Arch. Ophthalmol. 105:954, 1987. 20. Lugo, M., Donnenfeld, E. D., and Arentsen, J. J.: Corneal wedge resection for high astigmatism following penetrating keratoplasty. Ophthalmic Surg. 18:650, 1987. 21. Mandel, M. R., Shapiro, M. B., and Krachmer, J. H.: Relaxing incisions with augmentation sutures for the correction of postkeratoplasty astigmatism. Am. J. Ophthalmol. 103:441, 1987. 22. Judge, D., Gordon, L., Vander Zwagg, R., and Wood, T. O.: Refractive versus keratometric astigma tism postkeratoplasty. Refract. Corneal Surg. 6:174, 1990.
We performed cylindric corneal ablations with the excimer laser on 12 patients to correct severe, disabling astigmatism after keratoplasty. In some patients, an additional ablation was performed to correct myopia. Patients were followed up for an average of eight months (range, six to 14 months). Uncorrected visual acuity improved in nine patients, and nine of the 12 patients had a decrease in refractive cylinder at last follow-up. The mean preoperative refractive cylinder was 7.0 ± 3.6 diopters, which decreased to a mean of 3.1 ± 2.6 diopters at one month (P = .0003) and 4.3 ± 2.9 diopters at last follow-up (P = .03). Keratometric astigmatism decreased from 7.5 ± 3.9 diopters preoperatively to 5.2 ± 3.9 diopters at the last follow-up (P = .001). Mean spherical equivalent was reduced from - 7 . 4 ± 4.2 diopters preoperatively to —3.3 ± 4.4 diopters postoperatively (P = .003). Postoperative corneal haze, when present, did not reduce visual acuity. Excimer laser superficial keratectomy thus appears to be safe when used for postkeratoplasty ametropia, although substantial regression may limit its effectiveness in some patients. I HE OUTCOME of penetrating keratoplasty has improved with advances in microsurgical tech niques, more stringent criteria for selection of donor material, and better postoperative care. The visual recovery after such a surgical proce dure, however, is often adversely affected by
Accepted for publication June 26, 1992. From the Doheny Eye Institute, and Department of Ophthalmology, University of Southern California School of Medicine, Los Angeles, California. This study was supported by a grant from the Autry Foundation, Los Angeles, California (Dr. McDonnell). Reprint requests to Peter J. McDonnell, M.D., Doheny Eye Institute, 1450 San Pablo St., Los Angeles, CA 90033.
severe postoperative astigmatism despite a clear graft.1 Several surgical options have been described for correction of this postoperative astigmatism, but the results remain relatively unpredictable. 26 Photorefractive keratectomy with the 193-nm excimer laser is under investigation as an op tion for treatment of refractive errors and for excision of superficial cornea opacities. To cor rect myopia, a radially symmetric surgical pro cedure is performed with greater ablation depth centrally than peripherally 79 ; to excise superficial corneal opacities, a uniform ablation depth is used. 10 A nonradially symmetric ap proach to tissue ablation with flattening of the steep meridian for correction of corneal astig matism has been described in plastic spheres, animals, and human eyes.11·12 We used this tech nique for correction of severe astigmatism after keratoplasty.
Patients and Methods The laser used was a 193-nm argon-fluoride excimer laser (Twenty-Twenty, VISX, Inc., Sunnyvale, California). The detailed methods of this procedure have been described previous ly.1112 To correct astigmatism, a large-diameter laser beam is passed between a set of parallel blades. The separation between the blades is controlled by computer (with the slit opening during the procedure), and the resultant varia ble slit is used to control the laser delivery much as the iris diaphragm is used for correc tion of myopia. As in laser treatment to correct myopia, 240 steps are used. By using the slit, the resultant corneal flattening is only in the meridian perpendicular to the long axis of the slit (mechanical axis); no refractive change is intended along the mechanical axis. Alignment of the mechanical axis with the astigmatic axis of the patient is achieved by rotating the slit
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mechanism with computer control. Ablations were performed by using a fluence of 160 m j / cm2 and a repetition rate of 5 Hz. To calibrate the laser, we performed toric ablations in polymethylmethacrylate blocks and the induced cylinder was measured with a lensometer, as described previously. 11 Informed consent was obtained from all pa tients after the nature and risks of the proce dure were explained. To be eligible for the study, the patients must have had demonstrable improvement in visual acuity when corrected with the phoropter, but we did not require that they be correctable to 20/20. It was common for visual acuity to be correctable with contact lenses to a level one or two lines better than with spectacles, a consequence of a component of irregular astigmatism. Twelve patients were included in this study. None of these patients could tolerate contact lenses or the high cylindric correction needed in spectacles. Other sur gical options were offered to the patients. This investigational procedure is under a protocol approved by the Food and Drug Administration and the Institutional Review Board of the Uni versity of Southern California. Preoperative ex aminations included slit-lamp microscopy and photography for documentation. An experi enced examiner performed refraction, keratom etry, ultrasonic pachymetry, and computer-as sisted corneal topography preoperatively and postoperatively. The potential visual acuity was tested by contact-lens overrefraction or the Potential Acuity Meter if necessary (PAM, Men tor O & O Inc., Norwell, Massachusetts). Cor neal haze was graded preoperatively and post operatively as 0 (none), 0.5 (barely detectable), 1 (easily detectable, but not affecting refraction or retinoscopy), 2 (easily detectable and inter fering with retinoscopy and refraction), and 3 (obscuring iris details). The patients were then placed under the excimer laser, topical proparacaine hydrochloride was applied, and a circular protractor was placed on the globe at the corneoscleral limbus and oriented by using a landmark observed at the slit lamp preoperatively. A few pulses were then applied with the slit maximally narrowed to ensure proper orientation of the slit relative to the corneal cylinder and to acquaint the patient with the sensations associated with la ser ablation. The corneal epithelium was then removed with a blunt spatula, after which the eye was fixed by using a vacuum fixation ring, and the area of treatment centered over the entrance pupil, while the patient fixated on a
flashing centration light. The computer was programmed to perform cylindric ablations greater than or equal to 80% of the preoperative cylindric error, adjusted to the corneal plane. In one patient with postkeratoplasty astigmatism that measured 12 diopters, we programmed 50% correction and in two other patients a 66% correction was attempted. The desired refrac tive change was programmed into the computer in minus cylinder form (for example, piano - 6 . 0 0 x 180 designed to induce 6 diopters of flattening in the vertical meridian). The blades are oriented by the computer to be parallel to the axis of refractive cylinder expressed in mi nus cylinder form, thereby flattening the cornea in the appropriate (steeper) meridian. Patients were treated postoperatively with a combination tobramycin sulfate (0.3%)/dexamethasone sodium phosphate (0.1%) ointment and semipressure patching, and were examined daily or every other day until reepithelialization was complete. They were then treated with 1% prednisone acetate four times daily for two weeks, three times daily for four weeks, and twice daily for four more weeks. Two weeks and one, two, three, four, and six months postoper atively, refraction, keratometry, ultrasonic pachymetry, and computer-assisted topogra phy were performed by the same masked ob server. A paired two-tailed f-test was used to compare preoperative and postoperative meas urements. Data were computed as mean ± standard deviation.
Results Patients—We performed superficial toric ab lations with the excimer laser on 12 patients who had disabling postkeratoplasty astigma tism that had persisted for more than one year after removal of all corneal sutures. All patients were contact-lens intolerant and were unable to tolerate the high cylindric prescription in their spectacles. Prekeratoplasty diagnoses were keratoconus (Patients 3 through 6, 8, 9, 11, and 12), herpes (Patient 1), Fuchs' dystrophy (Pa tient 7), corneal scar (Patient 10), and chemical burn (Patient 2). Preoperative measurements disclosed that all patients except one (Patient 2) had potential visual acuity of 20/20. Patient 2, with a history of posttraumatic endophthalmitis, had a preoperative potential visual acuity of 20/60 as determined by the Potential Acuity Meter. Preoperative and postoperative refrac-
Photorefractive Keratectomy for Postkeratoplasty Astigmatism
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TABLE 1 PATIENT DATA* PREOPERATIVE
POSTOPERATIVE
VISUAL ACUITY
PATIENT NO.,
VISUAL ACUITY
GENDER,
REFRACTION
WITH CORRECTION
DESIRED CORRECTION
WITHOUT
WITH
(DIOPTERS)
WITHOUT CORRECTION
REFRACTION
AGE (YRS)
(DIOPTERS)
CORRECTION
CORRECTION
TIME (MOS)
1,M, 76 2, M, 37 3, M, 72 4, F, 27 5, F, 52 6, M, 44 7, F.83 8, M, 63 9, F, 29 10, F, 80 11,M, 46 12, M, 36
+3.50 -12.00 x 5 -0.75 -6,00 x 135 -6.50 -2.25 x 42 -3.00 -5.00 x 157 -9.25 -4.00 x 55 -4.00 -5.00 x 106 -1.00 -6.00 x 170 -5.00 -14.00 x 133 -13.25 -6.25 x 55 -6.50 -8.50 x 42 -2.75 -3.75 x 29 +2.50-11.00 x 135
3/200 20/400 20/400 20/100 20/400 20/200 20/300 20/400 10/400 5/200 10/200 20/400
20/40 20/100 20/30 20/30 20/30 20/30 20/30 20/100 20/20 20/30 20/25 20/20
Piano -6.00 Piano -10.00 -3.00 -2.25 Piano -4.75 -8.5 -3.75 Piano -4.75 -2.00 -4.00 -6.00 -12.00 -11.50-4.00 -2.75 -6.75 -1.75 -3.75 -10.00
Piano -8.00 x 178 Piano -2.75 x 18 -5.00 -2.75 x 25 +2.50 -0.50 x 6 -1.50 -6.00 x 33 + 1.50-10.50 x 113 -0.50+1.00 x 180 + 12.50 -6.00 x 148 +5.00 -2.50 x 64 +0.50 -3.00 x 144 +0.50 -3.50 x 111 +3.50 -6.00 x 136
20/400 20/100 20/400 20/30 20/400 3/200 20/25 20/300 10/200 20/100 20/80 20/100
20/25 20/60 20/30 20/20 20/20 20/30 20/20 20/50 20/20 20/30 20/20 20/25
9 14 7 12 7 6 6 6 6 7 6 7
"Corrected visual acuity represents visual acuity with spectacles.
tive error, visual acuity, and keratometric measurements were determined (Tables 1 and 2). The patients were followed up for a mini mum of six months, and for a mean of eight months (range, six to 14 months). Visual acuity—Uncorrected visual acuity im proved by at least one Snellen line in nine of 12 patients (75%), decreased by one line in one patient, and did not change in two patients (Table 1). The visual acuity corrected with spec tacles improved in seven patients by at least one line, decreased in one patient, and was unchanged in four patients. The visual acuity of Patient 6, whose uncorrected visual acuity ( 3 / 200) was improved markedly with spectacles (20/30), had even greater improvement ( 2 0 / 25) with a gas-permeable contact lens. Refractive astigmatism—Photorefractive ker atectomy was performed on the basis of the total measured refractive cylinder corrected for the corneal plane in most of the patients. The attempted correction was plotted against the achieved correction (Rz = 0.40) (Fig. 1). Patient 1, who had 12 diopters of astigmatism preoperatively, had a target correction of 6 diopters of cylinder, and Patients 7 and 9 had corneal ablations calculated to correct 66% of the initial refractive cylinder. The mean changes in refrac tive cylinder were determined (Fig. 2). The mean preoperative refractive cylinder was 7.0 ± 3.6 diopters. One month postoperatively, a significant reduction in refractive cylinder was achieved (3.1 ± 0.7 diopters, P = .001). A slight
regression in the effect was first noticed two months postoperatively, and the average cor rection at most recent follow-up was 38%. The difference in the axis of refractive cylinder preoperatively and at the last follow-up disclosed a shift in the axis that ranged from 1 to 173 degrees, with a mean shift of 58 ± 62 degrees. Four patients (Patients 1, 2, 4, and 10) had overcorrection of their astigmatism, with a shift in the cylinder axis of more than 100 degrees. TABLE 2 KERATOMETRIC CYLINDER*
PATIENT
PREOPERATIVE
POSTOPERATIVE
NO.
DIOPTER
AXIS
DIOPTER
AXIS
1 2 3 4 5 6 7 8 9 10 11 12
17.38 5.50 3.12 4.37 6.50 7.63 4.38 12.37 6.36 8.37 5.38 8.75
95 53 3 75 150 16 82 41 174 175 115 45
13.75 1.88 3.60 3.17 6.50 6.25 1.87 10.50 2.50 4.00 0.60 8.70
87 109 110 78 142 19 108 43 154 38 108 58
'Mean (± standard deviation) preoperative keratometric cyl inder, 7.5 ± 4.0; mean (± standard deviation) postoperative keratometric cylinder, 5.2 ± 3.9 (P < .001).
432
6-
Q
4"
y = 1.3568 + 0.67380X
R2
= 0.402 D
2-
oo •o
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AMERICAN JOURNAL OF OPHTHALMOLOGY
Ηχ·*
-2^,— ^
-4-
a
a
a
--— o
-6" -8'
-16
I
-14
'
l
-12
—
1
'
1
-10
Attempted
-2 Weeks After
Correction
Surgery
Fig. 1 (Campos and associates). Attempted correc tion vs achieved correction after photorefractive ker atectomy for correction of postkeratoplasty astigma tism.
Fig. 2 (Campos and associates). Refractive cylinder (mean ± standard error) over time after photorefrac tive keratectomy for correction of postkeratoplasty astigmatism.
Excluding these four patients with overcorrected astigmatism, the change in refractive cylin der axis was 20.3 ± 25 degrees. Keratometric astigmatism—The average pre operative keratometric corneal cylinder was 7.5 ± 3.9 diopters (Table 2). Considering the kera tometric cylinder at the last follow-up of each patient, the average corneal cylinder was 5.2 ± 3.9 diopters (P = .001). Nine patients had a decrease in the corneal cylinder of at least 1.3 diopters, two patients did not have any change in keratometric cylinder, and the other patient showed an increase in corneal cylinder of 0.48
diopter, although the uncorrected visual acuity in this patient (Patient 3) did not change. The mean changes in the keratometric cylinder were determined (Fig. 3). The maximum decrease in the keratometric cylinder was noticed within three months postoperatively. Spherical equivalent—The mean preoperative spherical equivalent was - 7 . 4 ± 4.2 diopters. The mean changes in the spherical equivalent were determined (Fig. 4). Within the first eight weeks postoperatively, the mean spherical equivalent approached zero, and represented a
-6-*
Weeks After Surgery
Fig. 3 (Campos and associates). Keratometric cylin der (mean ± standard error) over time after photore fractive keratectomy for correction of postkeratoplas ty astigmatism.
Weeks After
Surgery
Fig. 4 (Campos and associates). Spherical equiva lent (mean ± standard error) over time after photore fractive keratectomy for correction of postkeratoplas ty astigmatism.
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Photorefractive Keratectomy for Postkeratoplasty Astigmatism
hyperopic shift that persisted until 16 weeks (Fig. 4). A slight decrease in the surgical effect on the spherical equivalent was noticed after four months in most of the patients. At the six-month follow-up, Patient 3 had a substan tial regression of the surgical effect that had been present two months postoperatively (Fig. 5). Patient 4, with an intended cylindric correc tion of - 4 . 7 5 diopters, had a reduction in myopia from - 3 . 0 0 diopters preoperatively to - 1 . 0 0 diopters postoperatively (Fig. 6). Patient 6, with an intended correction of 5.00 diopters of cylinder, developed a hyperopic shift in the spherical error; at the last follow-up, mean spherical equivalent was —3.3 ± 4.4 diopters (P = .003). Pachymetry—The patients had a substantial decrease of the corneal thickness as an effect of excimer laser ablation. Two months postopera tively, the mean postoperative corneal thick ness increased temporarily (Fig. 7). At the last follow-up, the average corneal thickness was 0.46 ± 0.05 mm (P < .0001), with an average reduction of 0.09 ± 0.05 mm.
433
Complications—In one patient (Patient 2), the epithelial defect had healed by 11 days postop eratively, whereas in all the other patients the defect healed within three days postoperative ly. Patieht 1 developed recurrent herpes sim plex epithelial keratitis four weeks after keratoplasty (successfully treated with topical trifluridine). Another recurrence in this patient ten months after photorefractive keratectomy resulted in graft failure caused by apparent subsequent immunologie rejection. Despite fre quent admonitions to report immediately any possible problems, this patient did not inform us in both instances of the decrease in vision and development of conjunctival injection for a week or longer after onset of symptoms, which delayed initiation of appropriate therapy. Oth er possible complications, such as corneal re jection, infection, or recurrent erosions, did not develop in our patients. Corneal haze—The amount of corneal haze was graded by one of us (P.J.M.) for all patients. All of the corneas were graded as clear (0) preoperatively. The amount of haze postopera-
Fig. 5 (Campos and associates). Color-coded keratograph of Patient 3 obtained before (top left), at one month (top right), and seven months postoperatively (bottom left). The central cornea is less astigmatic at one month, but substantial regression of the surgical effect is noted at seven months.
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Fig. 6 (Campos and associates). Color-coded keratograph of Patient 4 obtained preoperatively (left) and eight months postoperatively (right). An overall flattening of the cornea was achieved, with apparent inferotemporal decentration of the zone of flattening. tively ranged from 0.5 (barely detectable) to 1.0 (easily detectable, but apparently not interfer ing with retinoscopy or refraction). Pain—The amount of pain experienced by these postkeratoplasty patients was generally mild and much less intense than that experi enced by most patients we have treated with photorefractive keratectomy who have not had previous keratoplasty or other corneal surgical procedures.
Discussion Although several techniques for correction of severe astigmatism after keratoplasty have been described, the refractive outcomes of these pro cedures, and particularly the predictability, are still unsatisfactory. 261316 The limited surgical success is probably related to a poor under standing of the donor-host tissue relationship, which might be affected by such factors as faulty surgical technique (trephination and su ture placement) and postoperative care. At tempts to correct postkeratoplasty astigmatism with relaxing incisions and compression su tures have yielded fairly unpredictable re sults. 16 Our results in this initial group of pa tients, after a single superficial ablation with the excimer laser, are not demonstrably superi or to results of other small published surgical series in which incisions and compression su tures were used. Whether re-treating patients with undercorrected astigmatism will improve our overall results is unknown.
We wanted to evaluate the safety and efficacy of toric superficial corneal ablations for reduc ing postkeratoplasty astigmatism. Analysis of the corneal reepithelialization rate showed that the wound healing was not delayed in these postkeratoplasty patients when compared with the previously described reepithelialization rate in patients after photorefractive keratecto my for correction of myopia.17,18 The delayed reepithelialization (11 days) in one patient may have been a consequence of the corneal alkali burn for which the keratoplasty was performed, and of mildly decreased tear production (con firmed by a preoperative Schirmer test). The 0.60-1
?
0.55
«I
«M t
0.50
5
0.45
O
0.40 H
1
1
1
1
1
1
1
0
4
8
12
16
20
24
28
Weeks After
Surgery
Fig. 7 (Campos and associates). Corneal thickness (mean ± standard error) as measured with ultrasonic pachymeter over time after photorefractive keratec tomy for correction of postkeratoplasty astigmatism.
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Photorefractive Keratectomy for Postkeratoplasty Astigmatism
amount of corneal haze in these patients was minimal and appeared not to affect the final vision. The absence of intraoperative complica tions and of postoperative corneal infections or graft rejections, and relatively minor pain ex perienced by these patients, suggest that this is a fairly safe surgical procedure. Other surgical techniques for correction of postkeratoplasty astigmatism have been associated with various intraoperative and postoperative complica tions; relaxing incisions have resulted in corne al abscesses19 and perforations,20 and allograft reactions have complicated wedge resections (Table 3).21 Uncorrected visual acuity improved in nine patients, but only two patients had uncorrected visual acuity of better than 20/40. All of our patients had best-corrected visual acuities of better than 20/60, which is comparable to pre vious results.1011 Nine of the 12 patients had a reduction in refractive cylinder to a level that was tolerable with spectacles. Disparity be tween refractive and keratometric cylinder and changes in each were common; Patient 6, for example, had a reduction of 1.4 diopters on keratometric cylinder, but an increase in refrac tive cylinder of 5.5 diopters. Other investiga tors82 have also demonstrated that refractive and keratometric cylinder may differ substan tially in postkeratoplasty patients. We observed a delayed loss of the initially achieved effect 12 weeks postoperatively (Fig. 5). It can be disappointing for patient and
435
surgeon alike to observe an initially excellent optical result at one or two weeks postopera tively be lost as regression occurs. Other studies using the excimer laser for refractive surgical procedures have shown a regression of the initial effect also, usually within one to three months postoperatively.1718 We looked for a re lationship between changes in corneal thick ness over time and regression of refractive effect postoperatively, but no correlation could be demonstrated in our patients. Patients 6, 8, and 12, who had the most regression of refrac tive change, had a stable, unchanging corneal thickness postoperatively, even during and af ter the regression. Other studies using the excimer laser for photorefractive keratectomy for myopia have indicated better results in patients whose pre operative myopia was less than 5.00 diop ters.17·18 In our study, we did not observe a similar correlation between preoperative cylindric error and the accuracy of the surgical outcome. In five patients we noted a corneal flattening in excess of that predicted merely on the basis of flattening the steep meridian. The preopera tive flat meridian, in which a uniform depth of ablation is created, was also flattened (Fig. 6). As we have noted before,12 this extra effect will have to be considered when programming an astigmatic correction with the excimer laser. Surgical management of disabling astigma tism after keratoplasty is currently unsatisfac-
TABLE 3 PREVIOUS STUDIES OF SURGICAL TREATMENT FOR POSTPENETRATING KERATOPLASTY ASTIGMATISM COMPARED WITH OUR STUDY PROCEDURE STUDY (IN ORDER OF PUBLICATION)
NO. OF
USED TO PLAN SURGICAL TECHNIQUE
REDUCTION OF
(DIOPTERS)
PERIOD (MOS)
4 16 14 21
Arcuate keratotomy
Keratometry
75.0
8.40
Arcuate keratotomy
Keratometry
42.5
4.25
4 8.2
Arcuate keratotomy
Keratometry
60.0
7.50
Not available
Arcuate keratotomy and Keratometry compression sutures
67.0
6.56
6 to 9
McCartney and associates19
11
Relaxing incisions and compression sutures
Intraoperative keratoscopy
68.0
7.95
13.5
Cohen, Tripoli, and Noecker14
7 5
Arcuate keratotomy
Photokeratoscopy
69.8
6.52
7
Arcuate keratotomy or relaxing incisions
Photokeratoscopy
37.7
3.00
Not available
7
Relaxing incisions and compression sutures
Computer-assisted corneal topography
81.1
8.20
12.3
Photorefractive keratectomy
Refraction
38.0
2.30
7.7
Troutman and Swinger3 Krachmer and FenzP Sugar and Kirk13 Mandel, Shapiro, and Krachmer2'
Maguire and Bourne15 Frangieh, Kwitko, and McDonnell" Our study
CASES
12
SURGICAL TECHNIQUE
ASTIGMATISM (%)
KERATOMETRIC CYLINDER REDUCTION POSTOPERATIVE
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tory. O n the basis of o u r r e s u l t s , t h e u s e of t h e excimer laser to p e r f o r m toric a b l a t i o n s in p a t i e n t s w i t h severe a s t i g m a t i s m after k e r a t o p l a s ty a p p e a r e d to be safe, b u t the refractive r e s u l t s r e g r e s s e d s u b s t a n t i a l l y in s o m e p a t i e n t s , t y p i cally at a b o u t or after t h r e e m o n t h s . We h a v e yet to r e - t r e a t any p a t i e n t s w i t h u n d e r c o r r e c t e d astigmatism, and thus cannot comment on w h e t h e r a r e p e a t surgical p r o c e d u r e w o u l d yield b e t t e r r e s u l t s .
References 1. Swinger, C. A.: Postoperative astigmatism. Surv. Ophthalmol. 31:219, 1987. 2. Lavery, G. W., Lindstrom, R. L., Hofer, L. A., and Doughman, D. V.: The surgical management of corneal astigmatism after penetrating keratoplasty. Ophthalmic Surg. 16:165, 1985. 3. Troutman, R. C , and Swinger, C : Relaxing inci sion for control of postoperative astigmatism follow ing keratoplasty. Ophthalmic Surg. 11:117, 1980. 4. Lindstrom, R. L., and Lindquist, T. D.: Surgical correction of postoperative astigmatism. Cornea 7:138, 1988. 5. Villaseflor, R. A., and Stimac, G. R.: Clinical results and complications of trapezoidal keratotomy. J. Refract. Surg. 4:125, 1988. 6. Krachmer, J. N., and Fenzl, R. E.: Surgical cor rection of high postkeratoplasty astigmatism. Relax ing incision vs wedge resection. Arch. Ophthalmol. 98:1400, 1980. 7. Marshall, J., Trokel, S„ Rothery, S„ and Krueger, R. R.: Photoablative reprofiling of the cornea using an excimer laser. Photorefractive keratectomy. Laser Ophthalmol. 1:21, 1986. 8. Taylor, D. M., L'Espérance, F. A., Jr., Del Pero, R. A., Roberts, A. D., Gigstad, J. E., Klintworth, G., Martin, C. A., and Warner, J.: Human excimer laser lamellar keratectomy. A clinical study. Ophthalmolo gy 96:654, 1989. 9. McDonald, M. B., Frantz, J. M., Klyce, S. D„ Beuerman, R. W., Varnell, R., Munnerlyn, C. R., Clapham, T. N., Salmeron, B., and Kaufman, H. E.: Central photorefractive keratectomy for myopia. The blind eye study. Arch. Ophthalmol. 108:799, 1990. 10. Stark, W. J., Gilbert, M. L., Goodman, G. L., Gottsch, J. D., Trokel, S., and Munnerlyn, C : Phototherapeutic keratectomy preliminary report. ARVO
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