|Year : 2012 | Volume
| Issue : 2 | Page : 222-226
Can opposite clear corneal incisions have a role with post-laser in situ keratomileusis astigmatism?
Hatem El-Awady, Asaad A Ghanem
Ophthalmology Center, Faculty of Medicine, Mansoura University, Egypt
|Date of Web Publication||21-Apr-2012|
Asaad A Ghanem
Ophthalmology Center, Faculty of Medicine, Mansoura University, Mansoura
Source of Support: None, Conflict of Interest: None of the authors has a financial or proprietary in any material or method mentioned. The authors alone are responsible for the content of the paper.
| Abstract|| |
Purpose: To evaluate the astigmatic correcting effect of paired opposite clear corneal incisions (OCCIs) on the steep axis in patients with residual astigmatism after laser in situ keratomileusis (LASIK)
Materials and Methods: Thirty-one eyes of 24 patients with a mean age of 28.4 years ±2.46 (range, 19-36 years) were recruited for the study. Inclusion criteria included residual astigmatism of ≥1.5 diopter (D) after LASIK with inadequate residual stromal bed thickness that precluded ablation. The cohort was divided into two groups; group I (with astigmatism ranging from -1.5 D to -2.5 D) and group II (with astigmatism > -2.5 D). The steep axis was marked prior to surgery. Paired three-step self-sealing opposite clear corneal incisions were performed 1-mm anterior to the limbus on the steep axis with 3.2-mm keratome for group I and 4.1 mm for group II. Patients were examined 1 day, 1 week, 1 month, 3 months and 6 months, postoperatively. Visual acuity, refraction, keratometry, and corneal topography were evaluated preoperatively and postoperatively. Analysis of the difference between groups was performed with the Student t-test. P<0.05 was considered statistically significant.
Results: The mean uncorrected visual acuity (UCVA) improved from 0.35±0.13 (range, 0.1-0.6) to 0.78±0.19 (range, 0.5-1) in group I and from 0.26±0.19 (range, 0.1-0.5) to 0.7±0.18 (range, 0.4-1) in group II. The increase in UCVA was statistically significant in both groups (P=0.001, both cases). The mean preoperative and postoperative keratometric astigmatism in group I was 2.0±0.48 D (range, 1.5-2.5 D) and 0.8±0.37 D (range, 0.1-1.4 D), respectively. The decrease in keratometric astigmatism was highly statistically significant in group II (P=0.001.). Mean surgically induced astigmatic reduction by vector analysis was 1.47±0.85 D and 2.21±0.97 D in groups I and II respectively. There were no incision-related complications.
Conclusions: Paired OCCIs were predictable and effective in correcting post-LASIK astigmatism and required no extra surgical skill or expensive instruments. OCCIs are especially useful in eyes with insufficient corneal thickness for LASIK retreatment.
Keywords: Clear Corneal Incisions, Post-Laser In Situ Keratomileusis astigmatism
|How to cite this article:|
El-Awady H, Ghanem AA. Can opposite clear corneal incisions have a role with post-laser in situ keratomileusis astigmatism?. Middle East Afr J Ophthalmol 2012;19:222-6
|How to cite this URL:|
El-Awady H, Ghanem AA. Can opposite clear corneal incisions have a role with post-laser in situ keratomileusis astigmatism?. Middle East Afr J Ophthalmol [serial online] 2012 [cited 2020 Sep 30];19:222-6. Available from: http://www.meajo.org/text.asp?2012/19/2/222/95256
| Introduction|| |
An important goal in corneal refractive surgery is to minimize postoperative corneal astigmatism after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK).  Surgical options to treat postoperative astigmatism include additional laser surgery (on the flat or steep meridians or both),  astigmatic keratotomy,  and peripheral corneal relaxing incisions (PCRIs). , The goal is to improve uncorrected visual acuity (UCVA) and reduce dependency on spectacles or contact lenses. Paired opposite clear corneal incisions (OCCIs) are commonly used in modern cataract surgery for effective control of preexisting astigmatism with the incision on the steepest meridian. , In the present study, we evaluate the safety, efficacy, and predictability of paired OCCIs for correcting astigmatism after LASIK in cases with inadequate corneal thickness for further ablation.
| Materials and Methods|| |
The study was carried out in accordance with the tenets of the Declaration of Helsinki (1989) of the World Medical Association. The study was approved by the Nokhba center trust ethics committee. All the patients were fully informed of the purpose and procedures of the study and written informed consent was obtained from all individuals.
Thirty-one eyes of 24 patients with residual post-LASIK astigmatism were included in the study. The mean age of the cohort was 28.4 ± 2.46 years.
Inclusion criteria for having OCCIs were: (1) patient dissatisfaction with UCVA; (2) refractive cylinder > 1.5 D for at least 3 months after LASIK; (3) stable refractive cylinder within ±0.5 D verified by manifest refraction (MR) at least 2 weeks apart; (4) no loss of BCVA from the original procedure; (5) no corneal disease that might interfere with corneal wound healing and; (6) insufficient corneal thickness for additional laser ablation.
Preoperatively the eyelids were cleansed with povidone iodine 5% and strict sterile technique was maintained intraoperatively. All OCCIs were performed under topical anesthesia with benoxinate hydrochloride 0.04%. The account for potential cyclotorsion, the steep meridian was marked prior to surgery while the patient sat upright. To ensure correct control of the incisions, two approaches were used:
When available, the meridian of prominent landmarks on the conjunctiva or limbus was noted and drawn relative to the 6 o'clock and 12 o'clock positions.
If a clear landmark was not evident by slit lamp biomicroscopy, the limbal corneal/conjunctival epithelium was at the 90° and 270° meridians with a Sinskey hook stained with gentian-violet.
Intraoperatively, a degree gauge was aligned with the 90° and 270° meridians, enabling identification of the surgical meridians. A side port incision was made in the corneal periphery distant from the steep meridian using a MVR blade. Healon was injected through the side port to make the anterior chamber deep and stable. A self-sealing 3-step corneal incision was performed with a 3.2-mm keratome (in group I) and 4.1-mm keratome (in group II) 1-mm anterior to the limbus on the steep meridian. The posterior lip of one incision was depressed to evacuate Healon from the anterior chamber. Finally, hydration of the side port incision was performed and topical antibiotic-corticosteroid combination drops were instilled. Patients were advised to be cautious during the early postoperative period and not rub or apply excessive pressure on the eye.
Postoperatively, patients were examined daily during the first week, then weekly during the first month, then every month for 6 months for the following:
- Slit-lamp biomicroscopy of the anterior segment.
- Assessment of best-corrected visual acuity (BCVA)
- Intraocular pressure measurement with Goldmann applanation tonometry.
- The mean arithmetic changes in refractive cylinder as measured by manifest refraction and changes in keratometric cylinder after laser ablation with the Wavelight Allegretto laser (Alcon Inc., Fort Worth, TX).
- Surgically induced astigmatism or reduction by vector analysis. 
- Incision-related complications.
The statistical analysis of data is performed by using an excel program and SPSS (SPSS, Inc, Chicago, IL) (version 10). Data are reported in mean (±) standard deviation for quantitative data. Analysis of the difference between groups was performed with the Student t-test. A P-value ≤ 0.05 was considered statistically significant at 95% confidence intervals (CI).
| Results|| |
The present study included 31 eyes of 24 patients with residual astigmatism after LASIK. Patients were divided into two groups: Group I included 16 eyes with astigmatism ranging between -1.5 D to -2.5 D that underwent 3.2-mm self-sealing paired OCCIs and; Group II included 15 eyes with astigmatism >-2.5 D that underwent 4.1-mm self-sealing paired OCCIs.
Seven patients underwent bilateral surgery. The mean age of all patients was 28.40 ± 2.46 years (range, 19-36 years). The mean age in group I and II was 29.80 ± 3.10 and 27.20 ± 4.20 years, respectively (P=0.34).
In group I, the mean UCVA was 0.35 ± 0.13 preoperative and 0.78±0.19, postoperatively. In group II, the mean UCVA was 0.26±0.14 preoperatively and 0.74 ± 0.18, postoperatively.
The change in UCVA from preoperative to postoperative was highly statistically significant in both groups (P=0.001). All eyes in group I and 93% of the eyes in group II had a postoperative UCVA of ≥ 0.5.
Change in astigmatism
The mean preoperative and postoperative corneal astigmatism was 2.00 ± 0.48 D (range, 1.50-2.50 D) and 0.80 ± 0.37 D (range, 0.-1.40 D), respectively in group I and 2.90 ± 0.29 D (range, 2.50-3.50 D) and 0.99 ± 0.43 (range, 0.30-1.90 D) respectively in group II [Figure 1].
|Figure 1: Preoperative and postoperative mean keratometric cylinder in both groups|
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There was a highly statistically significant reduction of keratometric astigmatism in both groups (P=0.001). In group I, 25% achieved a keratometric cylinder of ≤ 0.5 D while 62.5 % achieved keratometric cylinder of ≤ 1 D. In group II, 13.3% and 60% of eyes achieved keratometric cylinder of ≤ 0.5 D and ≤ 1 D, respectively.
The mean astigmatism correction was 1.17 ± 0.29 D (range, 0.55-1.45 D) in group I and 1.91 ± 0.39 (range, 1.20-2.65 D) in group II [Figure 2]. In group I, the mean magnitude of astigmatic correction on the steep horizontal axis was 1.10 ± 0.30 D and the mean magnitude of astigmatic correction on the steep vertical axis was 1.24 ± 0.10 D. There were no statistically significant differences between both types of astigmatic axis correction in group I (P= 0.18). In group II, the difference between horizontal axis correction (1.84 ± 0.43) and vertical axis correction (2.05 ± 0.3) was not significant (P=0.37).
Surgically induced astigmatic reduction
The mean reduction in SIA by vector analysis was 1.47 ± 0.85 D and 2.21 ± 0.97 D in group I and II respectively. There was a statistically significant reduction in SIA in both groups (P=0.009).
There were no OCCIs-related complications. The wounds were well sealed from the first postoperative day and the results were stable from the first postoperative week. There was no regression or progression of astigmatism during follow-up [Figure 3].
|Figure 3: Corneal topography of a patient with myopic astigmatism before laser in situ keratomileusis with astigmatic of 4.00 D (a), post-LASIK, the astigmatism was 3.30 D due to insufficient corneal thickness (b), and after self-sealing 4.10-mm OCCIs, the astigmatism decreased to 1.50 D (c)|
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| Discussion|| |
Astigmatism after refractive surgery can be surgically induced or residual due to under correction of preoperative astigmatism. The major determinants for astigmatic correction are the patient's desire for better UCVA. Generally, UCVA that is less than 0.5 due to refractive cylinder is an indication for correction. We prefer to perform a trial lens test on the affected eye to determine if the cylindrical correction will alleviate the visual symptoms. ,
Surgical options for reducing astigmatism include additional excimer laser ablation, astigmatic keratotomy, and peripheral corneal relaxing incisions (PCRIs). Excimer laser retreatment has been shown to be a safe and effective approach.  However, epithelial ingrowth can occur after flap relift or recut and secondary ablation after primary PRK or LASIK can cause central islands or ectasia. , In this study, LASIK was not considered due to insufficient corneal thickness.
Astigmatic keratotomy is another surgical option, and corrections of 3.00 D or more can be achieved in eyes with naturally occurring or postoperative astigmatism.  Kapadia and coauthors  report that paired accurate transverse incisions (Casebeer-Lindstrom nomogram) with a 7.00-mm diameter optical zone after PRK effectively reduce astigmatism and improve visual outcome. The major disadvantage of astigmatic keratotomy is that incisions are closer to the center of the cornea than with PCRIs; this requires cutting through the LASIK flap. Also, astigmatic keratotomy requires special instruments such as micrometer-step diamond knives and arcuate incision markers. In addition, the effect of astigmatic keratotomy is similar to that of radial keratotomy which fluctuates and may continue to fluctuate over several years. 
PCRIs generally involve incisions (600 μm ≤ deep) of varying sizes depending on the degree of astigmatism made on the steep corneal axis.
Wang et al,  evaluated the role of PCRIs after excimer laser refractive surgery. They reported that 61% of eyes gained UCVA of 20/20 and the refractive astigmatism was reduced significantly. The percentage of eyes within ± 0.50 D and 1.00 D of cylinder increased by 73% and 52%, respectively. PRCIs, also, require special instruments such as a diamond knife, and corneal marker, and require nomograms. 
OCCIs were used successfully to treat pre-existing astigmatism in cataract patients. , In light of the limitations of alternative approaches, OCCIs seem to be an excellent option to effectively reduce the astigmatism present after LASIK. To our knowledge, there are no previous reports on OCCIs to reduce post-LASIK astigmatism.
The potential advantages of OCCIs were as follows: (1) they are not performed on the corneal surface, hence, further surface irregularities done not occur; (2) the pupil is not a problem and does not adversely affect the outcomes (3) decentration is not problematic: (4) pachymetry is not important as in other refractive surgical procedures; (5) the procedure is easy requiring a short learning curve and; (6) a relatively minimal cost is required. Disadvantages of OCCIs include the theoretical risk of cataract and endophthalmitis because it is a penetrating procedure. Also, OCCIs are effective for mild and moderate degrees of astigmatism only.
In the present study, there was a statistically (and clinically) significant increase in UCVA. For example, 100% of eyes in group I and 93% of eyes in group II achieved UCVA of ≥ 0.5. There was also a significant reduction in the refractive cylinder and a corresponding significant increase in the percentage of eyes within ≤ 0.5 D (25% in group I and 13.3% in group II). In both groups, vertical OCCIs were more effective than horizontal OCCIs but there was no statistically significant difference between vertical axis and horizontal axis correction. The effect was stable up to 6 months, and there was no loss of BCVA. No patient reported postoperative infection, distortion in vision, glare, or discomfort.
Our results suggest that OCCIs are a practical, effective, and easily performed method for correcting astigmatism after LASIK especially in cases with insufficient pachymetry. The procedure did not require extra expertise or expensive surgical instruments. We believed that effective results can be expected under the guidance of the special nomogram considering variables such as incision length, width and distance from the limbus. Also, long term outcomes and a larger sample are necessary.
| Acknowledgment|| |
The authors thank Taha Baker for his care and diligence during writing the paper.
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[Figure 1], [Figure 2], [Figure 3]