Journal of Clinical Ophthalmology and Research

ORIGINAL ARTICLE
Year
: 2019  |  Volume : 7  |  Issue : 1  |  Page : 18--21

Reduction in preexisting against the rule astigmatism in temporal manual small incision cataract surgery: Can curvilinear incision be a better choice?


Karunanithy Palanisamy, P Amudha, R Amudhavalli, Ramalingam Munisamy, Arun Tipandjan 
 Department of Ophthalmology, Indira Gandhi Government General Hospital and Postgraduate Institute, Puducherry, India

Correspondence Address:
Karunanithy Palanisamy
Department of Ophthalmology, Indira Gandhi Government General Hospital and Postgraduate Institute, Puducherry
India

Abstract

Background: To address the issue of ATR astigmatism in patients who undergo temporal manual small incision cataract surgery (MSICS) surgery. Aim: The aim is to find out whether an incision that is made parallel to the limbus (curvilinear) while doing temporal MSICS can reduce the preexisting against-the-rule astigmatism (ATR). Settings and Design: The study was conducted on those patients who came for cataract surgery in a government general hospital. Materials and Methods: One hundred and five patients with cataract and ATR astigmatism of ≥1D were divided into three groups each with 35 patients. Group A patients underwent curvilinear incision temporal MSICS, Group B straight line incision temporal MSICS, and Group C limbal incision temporal phacoemulsification. The amount of change in ATR astigmatism in each group was calculated by comparing preoperative and postoperative keratometry readings. Statistical Analysis: All data were evaluated using SPSS version 19.0. To test the significant difference between pre- and post-operative astigmatism in each group, paired t-test was used. To test the significant difference in astigmatism between the three groups, ANOVA was used. Results: The reduction in the mean astigmatism in Group A was 0.89D, in Group B 0.62D, and in Group C 0.086D. The significant reduction of the ATR astigmatism in Group A and Group B could be due to the flattening of the horizontal curvature which is higher in patients with ATR astigmatism. Among these two groups, the curvilinear incision produced more flattening than the straight line incision. Conclusion: If a curvilinear (limbus parallel) is done while doing temporal MSICS in patients with higher ATR astigmatism, there can a significant reduction of ATR astigmatism giving a better uncorrected visual acuity.



How to cite this article:
Palanisamy K, Amudha P, Amudhavalli R, Munisamy R, Tipandjan A. Reduction in preexisting against the rule astigmatism in temporal manual small incision cataract surgery: Can curvilinear incision be a better choice?.J Clin Ophthalmol Res 2019;7:18-21


How to cite this URL:
Palanisamy K, Amudha P, Amudhavalli R, Munisamy R, Tipandjan A. Reduction in preexisting against the rule astigmatism in temporal manual small incision cataract surgery: Can curvilinear incision be a better choice?. J Clin Ophthalmol Res [serial online] 2019 [cited 2019 Mar 21 ];7:18-21
Available from: http://www.jcor.in/text.asp?2019/7/1/18/253991


Full Text



Phacoemulsification is the most modern method of cataract surgery achieving a very good uncorrected distance and near vision in most of the patients.[1] While the wound of the phacoemulsification produces minimal surgically induced astigmatism (SIA), the preexisting astigmatism is corrected by Toric intraocular lens (IOL), limbal relaxing incision (LRI), or incision on the steep axis.[2] MSICS is the most commonly performed cataract surgery in developing countries.[3] While the temporal approach produces the least SIA,[4] only very few satisfactory methods are available to correct preexisting astigmatism while doing MSICS.

The cataract incision is known to produce a flattening effect on the cornea. The curvilinear incision produces more flattening than other types of incisions such as straight-line, chevron, and smile.[5]

Against-the-rule (ATR) astigmatism is more common in old age, wherein the horizontal curvature is more curved than the vertical curvature.[6],[7],[8],[9] It can be postulated that a curvilinear incision on the temporal side can produce a desirable flattening effect on the more curved horizontal axis which is seen in patients with ATR astigmatism.

This study was done to find out whether an incision that is made parallel to the limbus (curvilinear) while doing temporal MSICS can reduce the preexisting ATR astigmatism. The aim of the study was to compare the change in the amount of astigmatism caused by temporal curvilinear incision MSICS with the change in the amount of astigmatism caused by temporal straight line incision MSICS and temporal incision phacoemulsification in patients with preexisting ATR astigmatism of >1D.

 Materials and Methods



One hundred and five eyes of 105 patients who had visually significant cataract of grades two to three nuclear sclerosis with ATR astigmatism of 1D or more than 1D were included in the study. Patients having traumatic cataract, complicated cataract, and other ocular ailments were excluded from the study.

The patients were assigned to three groups of 35 each. Group A underwent curvilinear incision temporal MSICS, Group B underwent straight-line incision temporal MSICS, and Group C limbal incision temporal phacoemulsification. A thorough preoperative workup including slit-lamp examination, measurement of intraocular pressure, patency of nasolacrimal duct, and fundus examination was done in all patients. Both manual (Bausch and Lomb) and automated keratometry (Topcon Autorefractor Keratometer) were done to calculate the preoperative corneal curvatures. Both manual and automated K readings were taken to ensure the accuracy of the presence of against the rule astigmatism among the study participants and automated K reading values were taken for analysis. No statistically significant difference in astigmatism was observed in our study population between manual and automated K readings.

Surgery was done after examining the general condition and after obtaining fitness from physician wherever necessary.

Block randomization method was used to randomize the three methods of surgery. Before surgery patients were given a cover with a randomized group name such as A, B, and C for three different techniques. Surgery was done based on the technique specified in the sealed cover. All surgeries were done by the same surgeon.

Group A: After making the conjunctival flap, a curvilinear incision which was parallel to the limbus with a chord length of about 6.5–7 mm was made on the external sclera 2 mm away from the limbus. A sclero corneal tunnel was made with a crescent blade and anterior chamber was entered with keratome. After doing capsulorhexis, the nucleus management was done in the usual way. After thorough cortical wash, posterior chamber IOL was implanted [Figure 1]Group B: All the procedures were the same as done for Group A, except that the incision on the external sclera was a straight line incision of 6–7 mm lengthGroup C: Temporal limbal three plane incision using a blade and a 2.8 mm keratome was made and phacoemulsification method of surgery was done. Foldable IOL of the appropriate power was implanted.{Figure 1}

All the patients were examined on days 1, 7, 30. and 45. Uncorrected visual acuity and best-corrected visual acuity were recorded in each visit. Three keratometry readings were taken in each visit using both manual and automated keratometers and the average value was used for analysis. Postoperative inflammation was managed with topical antibiotic-steroid drops and homatropine 1% drops was used as a cycloplegic.

The amount of astigmatism in preoperative and postoperative patients was calculated by the subtraction method, that is, by subtracting the vertical meridian from the horizontal meridian in this study (as the cases chosen were having only ATR astigmatism, wherein always the horizontal curvature was greater than the vertical value). Similar method was used to calculate the mean induced astigmatism in the study by Kongsap.[10]

Scientific and ethics committee approval was obtained for the study in accordance with the tenets of the Declaration of Helsinki of 1975 as revised in 2000. Written informed consents were obtained from all patients before including them in the study. Data were analyzed using IBM SPSS Statistics for Windows, Version 19.0 (IBM Corp., Armonk, NY, USA). To test the significant difference between pre- and post-operative astigmatism in each group, paired t-test was used. To test the significant difference in astigmatism between the three groups, ANOVA was used.

 Results



Of the 105 patients in the study, 46.7% (49) were male patients and 53.5% (56) were female patients. The age-wise distribution showed only three patients were <50 years and the rest were above 50 years. The types of surgery were equally distributed with 33.3% in all the three groups with 35 participants in each.

The right eye of 52 patients and the left eye of 53 patients were operated. As the keratometry values from manual and automated keratometer were almost similar and the values from automated keratometer were preferable, the values from automated keratometer were analyzed in this study.[11] Suturing was not required in any of the patients and no wound-related complications like wound dehiscence or iris prolapse were noted.

The mean preoperative astigmatism was 1.814 ± 1.02D in Group A, 1.566 ± 0.76D in Group B, and 1.471 ± 0.66D in Group C. The mean astigmatism on the 45th postoperative day was 0.921 ± 0.75D in Group A, 0.957 ± 0.59D in Group B, and 1.386 ± 0.76D in Group C. A reduction in the amount of ATR astigmatism was noticed in Group A and B. The mean astigmatism in Group A reduced from 1.814 to 0.921 and in Group B from 1.566 to 0.957. The Group C patients had a mild reduction in the mean astigmatism from 1.471 to 1.386. Paired t-test between preoperative and 45th postoperative day astigmatism showed a t = 8.66 (P < 0.01) in Group A, 9.434 (P < 0.01) in Group B, and 1.974 in Group C (P > 0.05) suggesting a statistically significant decrease in astigmatism in Group A and Group B patients and no statistically significant decrease in astigmatism in Group C patients [Table 1]. The mean uncorrected visual acuity (UCVA) on the 45th postoperative day for Group A was 6/12, for Group B was 6/12 and for Group C was 6/18.{Table 1}

ANOVA with repeated measure with a between factor suggests the presence of both a main effect and an interaction effect. Since Mauchly's test of significance is statistically significant P < 0.001, we interpret the Greenhouse–Geisser F-test and conclude a statistically significant main effect for astigmatism F (1.56, 159.63) =23.59, P < 0.001, and a statistically significant in the type of surgery and astigmatism interaction effect F (3.13, 159.63) = 5.449, P < 0.005 favoring curvilinear type of surgery to minimize astigmatism (Curvilinear M = 0.92, Straight line M = 0.95, and Phaco M = 1.39) [Figure 2].{Figure 2}

 Discussion



While operating cataract patients with preexisting astigmatism using phacoemulsification method, several choices such as Toric IOL, operating on steep axis, making opposite clear corneal incisions, and LRI can be offered to correct their preexisting astigmatism and give them a very good uncorrected distance visual acuity. However, in MSICS, the common method of cataract surgery in developing countries like India, the problem of preexisting astigmatism is yet to be solved. The temporal approach gives a better result with the least SIA, but it is not offering any advantage to patients with higher amount of preexisting astigmatism, and thus lower uncorrected visual acuity is only achieved in these patients.

Incisions placed in superior quadrant induce larger SIA and also the preexisting ATR astigmatism can only increase with these incisions;[1] only patients with-the-rule (WTR) astigmatism are benefitted from these superior quadrant incisions.[12] ATR astigmatism, wherein horizontal meridian is more curved than the vertical meridian is more common in aged patients who require cataract surgery.[6],[7],[8],[9] A curvilinear incision (limbus parallel) near the temporal limbus is capable of flattening the horizontal meridian. Hence, this study was conducted to look for any benefit in the decrease in ATR astigmatism that can occur if MSICS is done with temporal curvilinear incision and also to compare this with the reduction of ATR astigmatism that can occur when done by temporal straight line incision MSICS and temporal phacoemulsification.

The mean preoperative astigmatism of all the 105 cases that were included in the study was ATR astigmatism 1.617 ± 0.832 and their mean astigmatism on the 45th postoperative day was 1.088 ± 0.731. There is a statistically significant difference between the mean preoperative astigmatism and the mean 45th postoperative day astigmatism with a t = 4.89 and P < 0.01. This shows that temporal approach is advantageous for the patients with the ATR astigmatism of 1D or more as these patients have a steeper horizontal curvature. The advantage of temporal incision over superior incision has been proved in several similar studies.

In the study of Gokhale and Sawhney,[4] the SIA in the superior MSICS group was 1.28D, in the superotemporal group 0.2D, and in the temporal group 0.37D, and they have concluded that the temporal approach was better than superior approach. In the study of Mallik et al.,[13] on comparing MSICS by superior and temporal approaches, they have concluded that temporal approach provided better stabilization of refraction than the superior approach. The frequency distribution of the preoperative and the 45th-day postoperative astigmatism in Groups A and B show a clear shift in the pattern of astigmatism toward neutralization on the 45th-postoperative day.

Analysis of astigmatism in each group reveals that the mean astigmatism has reduced by 0.89D in Group A patients (from 1.80 ± 1.02 to 0.92 ± 0.75). This change in astigmatism is statistically significant with t = 8.66 and P < 0.01. The possible cause of this reduction is probably the flattening effect of the incision on the corneal curvature. It is a well-known fact that following a scleral incision, tissue gap, or slippage occurs producing a flattening along the meridian of the incision and steepening 90° away.[1] Radwan[12] advocates superior incision for patients with WTR astigmatism as he found that there was a flattening of the vertical curvature in these patients. In the present study, temporal incision was done to flatten horizontal curvature which was more in patients with ATR astigmatism.

In Group B, the mean astigmatism has reduced by 0.62D (from a mean preoperative value of 1.57 ± 0.76 D to a mean postoperative value of 0.95 ± 0.59D). This reduction is also statistically significant with a t = 9.434 and P < 0.01. Temporal straight line incision also produces a flattening effect on the horizontal curvature of the cornea. This observation compares well with the previous studies that have shown very less induction of SIA in the temporal approach.[4],[14],[15]

In Group C, the mean astigmatism has reduced by only 0.086D (from 1.47 ± 0.66 to 1.39 ± 0.76). This change is not statistically significant as the t = 1.974 and P > 0.05. The incision size used for phacoemulsification is not known to induce any significant change in the curvature of cornea. Hayashi et al.[16] showed that the maximum incision size that did not induce any significant change in corneal shape was approximately 3.2 mm.

The patients who have undergone phacoemulsification in this study would have done better with additional procedures such as LRI, Toric IOL for the correction of their preexisting astigmatism. However, those who were operated with temporal curvilinear incision or straight line incision had a statistically significant change in astigmatism toward neutralization and had a better UCVA on the 45th-postoperative day.

The ANOVA with repeated measures done to find out the significant difference in the mean astigmatism among three groups showed that the changes in Group A were more statistically significant than the other two groups. From this, it can be inferred that the curvilinear incision temporal MSICS produced a more desirable change in ATR astigmatism than the straight line incision temporal MSICS or phacoemulsification in this study.

 Conclusion



If a small modification in the incision from straight line to curvilinear (limbus parallel) in patients with higher ATR astigmatism is made while doing temporal MSICS, there can be reduction of ATR astigmatism giving a better UCVA which can be better than doing a phacoemulsification without LRI or Toric IOL in these patients. This is a useful modification that can be followed in developing countries like India, where MSICS is the most commonly done cost effective cataract surgery.

However, no effort was made in this study to quantify the exact amount of neutralization of ATR astigmatism that can occur with these incisions. Further studies are required to look for long-term stabilization of these changes in ATR astigmatism. The limitation of the study is that neither SIA calculator nor vector analysis was used to calculate the SIA.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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