Year : 2000 | Volume
: 48 | Issue : 2 | Page : 113--8
Fellow eye treatment in excimer photo refractive keratectomy
SK Rao, BN Mukesh, AS Saraniya, G Sitalakshmi, P Padmanabhan
Medical Research Foundation, Chennai, India
S K Rao
Medical Research Foundation, Chennai
Purpose: To describe symmetry of response in fellow eyes of patients undergoing photorefractive keratectomy (PRK) for myopia, analyse the risk factors leading to asymmetry in response and to determine if delayed treatment of the second eye increases safety and predictability of PRK.
Methods: Retrospective review of case records of 133 patients who underwent bilateral myopic PRK and had a minimum follow up of 6 months in both eyes.
Results: Postoperative uncorrected visual acuity, spherical equivalent (SE) refraction within ±1D of emmetropia, best-corrected visual acuity (BCVA) and corneal haze were not significantly different in fellow eyes of patients undergoing PRK for myopia. Of 87 eyes in group 1 (myopia <6D), 96.6% had uncorrected visual acuity ≥6/ 12, 89.7% were within ±1D of emmetropia, none lost ≥1 line BCVA, and none had haze ≥grade 3. Similar results for 98 eyes in group II (myopia 6 to 9.9D) were 75.6%, 55.1%, 2.0% and 2.0% respectively. For 81 eyes in group III (myopia ≥ 10D) the results were 42.7%, 33.3%, 8.6%, and 4.9% respectively. Among 84 patients with similar preoperative myopia in both eyes, 54 (64.3%) patients had a postoperative SE difference ≤ ID in fellow eyes. Risk factors for asymmetric response among fellow eyes included increasing preoperative myopia (p<0.001) and dissimilar treatment technique in the two eyes (p=0.03). Corneal haze did not increase significantly after the third postoperative month.
Conclusion: This study demonstrates that considerable symmetry of response exists in fellow eyes of patients undergoing myopic PRK. Early PRK in the fellow eye of patients with < 6 D myopia is safe and allows quick visual rehabilitation of the patient. In patients with myopia ≥6D, a 3-month interval before treating the second eye may improve the safety of the procedure.
|How to cite this article:|
Rao S K, Mukesh B N, Saraniya A S, Sitalakshmi G, Padmanabhan P. Fellow eye treatment in excimer photo refractive keratectomy.Indian J Ophthalmol 2000;48:113-8
|How to cite this URL:|
Rao S K, Mukesh B N, Saraniya A S, Sitalakshmi G, Padmanabhan P. Fellow eye treatment in excimer photo refractive keratectomy. Indian J Ophthalmol [serial online] 2000 [cited 2022 May 17 ];48:113-8
Available from: https://www.ijo.in/text.asp?2000/48/2/113/14893
Since its introduction in 1983, excimer photorefractive keratectomy (PRK) has undergone numerous modifications in surgical technique and instrumentation.[1,2] Excimer laser surgery is now considered the treatment of choice for the correction of myopia and astigmatism. Timing of the procedure in two eyes of a patient, however, is not clear. Simultaneous or early treatment of the fellow eye results in quick visual rehabilitation and a single convalescence period for the patient, without troublesome anisometropia. Concerns with this approach include the risks of over/ under correction and development of corneal haze in both eyes, resulting in visual instability. Treating both eyes in a staged manner allows the patient to assess functional outcome in the first eye, before treatment of the second eye - a dense corneal scar in the first eye may result in the patient declining treatment in the fellow eye. Theoretically, this approach also allows the surgeon to "fine-tune" the procedure in the second eye, resulting in a better outcome.
Although previous studies have described symmetry of results in fellow eyes of patients undergoing radial keratotomy, only one study has attempted to address this issue in patients undergoing PRK for myopia.[4,6,7] In this study we analyzed symmetry of outcome in fellow eyes of patients undergoing PRK for myopia, comparing uncorrected visual acuity, loss of one or more lines of best-corrected visual acuity, postoperative spherical equivalent within ±1 diopter (D) of emmetropia, and degree of corneal haze. Risk factors responsible for asymmetry of response are described. We also attempted to determine if the surgeon was able to achieve a more satisfactory outcome in the second eye, based on treatment results in the first eye.
Materials and Methods
We retrospectively analysed records of 458 patients who underwent excimer laser PRK for correction of myopia at our institute, between February 1994 and December 1996. 265 (57.86%) patients had bilateral treatments and of these, 133 (50.18%) patients had at least 6 months follow-up in both eyes. Information obtained from case records of these 133 patients included patient age and gender, pre- and postoperative manifest refraction and best-corrected visual acuity (BCVA), treatment details, postoperative uncorrected visual acuity (UCVA), and degree of corneal haze. All patients underwent routine ophthalmic examination and informed consent was obtained prior to the procedure. Exclusion criteria included age less than 18 years, unstable refraction, corneal ectasia, lid margin disease, and rheumatoid arthritis. Contact lens wearers discontinued use of the lens for at least 2 weeks prior to surgery. Corneal topographic evaluation (Corneal modeling system, Computed anatomy Inc., New York, NY) was performed prior to the procedure to exclude contact lens induced warpage.
Eighty two (61.7%) patients had the second eye treated a minimum 3 months after the first procedure. Other patients (38.3%) underwent treatment in the fellow eye within 3 months of the first procedure. All procedures were performed with the Summit Omnimed UV 200 excimer laser (Summit Technology, Inc., Waltham, MA). Topical 2% pilocarpine was instilled in the eye to be treated, half an hour prior to the procedure. The PRK was done in supine position after instilling several drops of 4% lidocaine. The fellow eye was patched, to aid fixation with the eye undergoing treatment. After inserting a wire speculum to separate the eyelids, a training session was performed to familiarize the patient with the sound and feel of the operating laser. A circular mark, 1 mm larger than the diameter of the intended ablation zone, was made on the epithelium using a blunt corneal trephine. The mark was centred on the pupil with the patient fixating on the coaxial fixation light in the laser delivery tube. Manual debridement of the epithelium within the marked zone was performed using a Grieshaber scarifier (Grieshaber and Co., AG, Switzerland). Debris on the surface of the corneal stroma was removed with a moistened week-cell sponge (Merocel Corporation, Mystic, CT) before laser treatment. At the conclusion of the procedure, the eye was patched with 0.3% ciprofloxacin eye ointment. Oral analgesics were prescribed.
The patients were reviewed daily and patching repeated till epithelialization was complete. Topical steroids were commenced on the day after treatment and included topical betamethasone, one-eighth dilution of commercially available 0.1% eye drops, or 0.1% fluorometholone eye drops, according to the preference of the three treating surgeons. Topical steroids were used in tapering doses for 4 months. Follow-up visits were scheduled at 1, 3, 6, and 12 months, and at yearly intervals thereafter.
During postoperative visits, UCVA, manifest refraction and BCVA, and intraocular pressure (IOP) were recorded. The degree of corneal haze was assessed by slitlamp biomicroscopy using the grading system shown in Table 1. For analysis, eyes were grouped according to the preoperative myopic spherical equivalent as follows: Group I-myopia <6.0D; Group III - myopia 6.0 to 9.9D; Group III -myopia ≥10.0D.
Frequencies and descriptive statistics were computed using SPS5/ PC+ statistical software. Adjusted chi-square approach for categorical data and paired t-test for continuous data were used to test association of risk factors with asymmetric treatment response in fellow eyes. Change in corneal haze at different follow-up visits and difference in haze in fellow eyes was tested by Wilcoxon-signed rank test, p ≤ 0.05 was considered to be statistically significant.
Mean age of the study population was 26.6 ± 5.9 years (18 - 53 years), with a male preponderance (60.9%). Average follow up was 16.5 ± 8.6 months (6 - 40 months). All patients had minimum 6 months follow-up in both eyes and 88 (66.2%) patients had minimum 1- year follow up in both eyes. Mean preoperative spherical equivalent (SE) in the first eye was -8.2 ± 3.5D (-2.5 to -18.5D), and in the second eye was -7.9 ± 3.7D (-2.3 to -20.3D). Ablation diameters ranged from 5 to 6.5 mm and both single-zone and multizone treatments were performed. One hundred (75.2%) of the first eyes and 91 (68.4%) second eyes had single-zone treatment. Of the 33 first eyes treated with a multizone technique, 23 (69.7%) underwent an aspheric multizone procedure and 10 (30.3%) were treated with a multizone multipass technique. Similarly, among 42 second eyes undergoing multizone treatment, 24 (57.1%) underwent an aspheric multizone procedure and 18 (42.9%) underwent a multizone multipass procedure. Average number of pulses used for treating first eyes was 307.5 ± 75.1(145 to 617) and second eyes was 293.7 ± 84.3 (145 to 640). Mean postoperative SE in the first eye at last follow up was -1.4 ± 2.2D (-11.5 to 1.8D) and in the second eye was -1.0 ± 2.3D (-13.0 to 2.0D).
Uncorrected visual acuity ≥20/40, loss of BCVA ≥1 line, postoperative SE within ± 1D of emmetropia and corneal haze ≥ grade 3 in the three myopia groups for first and second eyes are listed in [Table:2]. None of these results were significantly different in the two eyes. Similar data for both eyes of 51 patients who underwent bilateral procedures with an interval of less than 3 months and 82 patients who had second eye treatment 3 months or more after the first eye are listed in [Table:3] and [Table:4] respectively. The results in the first and second eyes were not significantly different in both groups of patients. All the above results are from the last equivalent follow up in both eyes.
Changes in postoperative SE with time were similar in both eyes, as shown in [Figure:1] and [Figure:2]. Corneal haze was similar in both eyes at all follow-up visits, in all myopia groups ([Table:5] and [Table:6]). No statistically significant worsening of corneal haze was noted after the 3-month visit. A tendency towards a myopic shift in refraction beyond the third month was noted, especially in patients with preoperative myopia >6.0D.
Among 133 patients in this study 84 (63.2%) had similar preoperative myopic SE in both eyes (difference <1D). Fifty four (64.3%) of these 84 patients had a postoperative SE difference ≤ 1D in the two eyes. Risk factors for postoperative asymmetry (difference in postoperative SE > 1D at last equivalent follow up in the two eyes) included dissimilar treatment techniques (single versus multizone) in two eyes (p=0.03), and increasing myopia (p<0.001) as shown in [Table:7]. The choice of postoperative steroid did not influence symmetry of postoperative response.
Among 84 patients with similar preoperative myopia, an attempt was made by the operating surgeon to modify treatment in the second eye, based on first eye results, in 12 patients [Table:8]. Modification in treatment strategy included an intentional overcorrection in the second eye and/or use of a multizone technique, if undercorrection was noted in the first eye.
Treatment results in this study are similar to those reported by us earlier and by other investigators.[5,9-11] Best results are achieved in patients with <6.0D of myopia. Considerable symmetry of response occurs in fellow eyes of patients [Table:2]. Better outcomes in the second eye could reflect our policy of treating the more myopic eye first. However, none of the observed differences attained statistical significance.
Among patients with similar preoperative myopia (n=84), 64.3% had a difference in postoperative SE ≤ 1D in the 2 eyes. This is less than the 75% reported by Lowenstein et al and could reflect the higher myopia treated in this series (-8.2D and -7.9D in the first and second eyes respectively), compared to Loewenstein's series (-6.2D in either eye). Significant increase in asymmetry with increasing preoperative myopia was noted in this series [Table:7].
The timing of treatment in the fellow eye did not affect the observed outcome symmetry in fellow eyes ([Table:3] and [Table:4]). Slightly better outcomes in patients undergoing second eye treatment within 3 months of the first eye, reflect the lesser myopia in this group of patients. In general, patients in this series with >6 D of myopia were advised to wait 3 months before considering treatment of the second eye. Another risk factor for asymmetric response in fellow eyes of patients was the use of different treatment techniques in the two eyes. Better outcomes with multizone treatments have also been highlighted in recent reports.[12-14]
In 6 of 12 patients in whom the surgeon attempted to modulate treatment parameters for the second eye based on the first eye results [Table 8], patients # 2,5,6,7,10,11), a better outcome was obtained in the second eye. In three patients (patients # 1,4,9), the second eye fared worse than the first eye. In three others (patients # 3,8,12), indeterminate results were obtained. At the time of treating the second eye, modification of treatment parameters based on first eye results may help achieve a better outcome, though studies with larger numbers of patients are required to further clarify this issue.
Given the excellent safety and predictability of the procedure in patients with myopia <6D, we recommend early treatment of the second eye in these patients. With the advent of laser in-situ keratomileusis (LASIK), excimer PRK is no longer used for the treatment of high myopia (≥ 10D) by us. In patients with myopia of 6 to 9.9D, the predictability and safety of PRK in our hands appears to be less. If these patients opt to undergo PRK, we recommend a 3-month interval before treating the fellow eye. A 3-month follow-up period was sufficient to detect patients who developed significant haze in this study. Therefore, if a satisfactory result is obtained at this time in the first eye, given the symmetry of outcome, we feel that the second eye can be safely treated. An unsatisfactory refractive outcome or severe corneal haze in the first eye allows the patient to function with the unoperated eye till the surgeon is able to correct the complication in the first eye. This approach requires that the patient tolerate a 3-month period of anisometropia. However, since a considerable number of these patients use contact lenses, they are able to function using the contact lens in the unoperated eye. This has also been described in another study in which 25.2% of 341 patients did not receive PRK in the second eye within one year of follow-up.
In conclusion, our results indicate that considerable symmetry of outcome exists between fellow eyes of patients undergoing PRK for myopia. Our data also confirms the excellent safety and efficacy of excimer PRK in the treatment of myopia < 6D. We therefore, recommend early treatment of the fellow eye in patients with less than 6D of myopia. However, in higher myopes it may be prudent to delay treatment of the second eye by at least 3 months to increase the safety and possibly the predictability of the procedure.
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