A clinical study comparing post-operative astigmatism with straight and frown scleral incision in manual small incision cataract surgery

DK Seethalakshmi; Anoosha Prakash; Savita Kanakpur; Lakshmi Bomalapura Ramamurthy

doi:10.4103/mjhs.mjhs_47_22

ORIGINAL ARTICLE

Year : 2023 | Volume : 11 | Issue : 2 | Page : 138-142

A clinical study comparing post-operative astigmatism with straight and frown scleral incision in manual small incision cataract surgery

DK Seethalakshmi, Anoosha Prakash, Savita Kanakpur, Lakshmi Bomalapura Ramamurthy
Department of Ophthalmology, Karnataka Institute of Medical Sciences, Hubballi, Karnataka, India

Date of Submission	08-Jul-2022
Date of Decision	12-Aug-2022
Date of Acceptance	08-Sep-2022
Date of Web Publication	18-Apr-2023

Correspondence Address:
Lakshmi Bomalapura Ramamurthy
Department of Ophthalmology, Karnataka Institute of Medical Sciences, Hubballi, Karnataka
India

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/mjhs.mjhs_47_22

Abstract

Background: Cataract surgery is considered refractive surgery. Apart from implanting the right dioptric power of Intra ocular lens (IOL), minimizing postoperative astigmatism plays an important role in good visual rehabilitation. Hence, surgical incision is of major importance in minimizing postoperative astigmatism and reducing or abolishing preexisting astigmatism.
Objectives: The objective of this study is to compare surgically induced astigmatism (SIA) following straight and frown scleral incisions in manual small-incision cataract surgery (MSICS).
Materials and Methods: This is a prospective randomized comparative study conducted among two groups of patients undergoing MSICS, where the straight scleral incision was performed in one group with 29 cases and the frown incision was performed in the other group with 29 cases. Postoperatively, patients were followed up on postoperative day 1, week 1, and week 6. Uncorrected visual acuity, Kv and Kh readings, and SIA were noted at each postoperative visit.
Results: SIA on the postoperative day 1 in the straight incision group (SIG) was 1.4914D ± 1.251 and in the frown incision group (FIG) was 0.629D ± 0.288. On the postoperative week 1 in SIG, it was 0.9655D ± 0.699, and in FIG, it was 0.474D ± 0.397. On the postoperative week 6 in SIG, it was 0.8793D ± 0.599, and in FIG, it was 0.414D ± 0.286. SIA was significantly less in FIG compared to SIG (P = 0.011). Postoperative uncorrected visual acuity was better in FIG compared with SIG. More amount the rule astigmatism was noted in FIG on the postoperative 6^th-week follow-up, which is favorable to the patient, while SIG witnessed more amount against the rule astigmatism.
Conclusion: Frown incision is a better incision than the straight incision in MSICS to create a sclerocorneal tunnel.

Keywords: Frown incision, manual small-incision cataract surgery, straight incision

How to cite this article:
Seethalakshmi D K, Prakash A, Kanakpur S, Ramamurthy LB. A clinical study comparing post-operative astigmatism with straight and frown scleral incision in manual small incision cataract surgery. MRIMS J Health Sci 2023;11:138-42

How to cite this URL:
Seethalakshmi D K, Prakash A, Kanakpur S, Ramamurthy LB. A clinical study comparing post-operative astigmatism with straight and frown scleral incision in manual small incision cataract surgery. MRIMS J Health Sci [serial online] 2023 [cited 2023 May 29];11:138-42. Available from: http://www.mrimsjournal.com/text.asp?2023/11/2/138/374279

Introduction

Cataract is one of the most common causes of visual impairment in the world. According to the World Health Organization (WHO), cataract is the leading cause of blindness worldwide, responsible for 47.8% of blindness and accounting for 17.7 million blind people.^[1] According to the WHO's latest assessment, age-related cataract is responsible for 51% of world blindness.^[2]

There are a large number of cataract patients waiting in our country, mainly in the suburban and rural populations to undergo surgery. The mainstay of the treatment for vision restoration is cataract surgery. Cataract surgery is one of the most common procedures performed worldwide.^[3]

Cataract surgery has evolved tremendously since the time it was first performed. In the present day, cataract surgery is not only performed as a procedure to improve the quality of vision but is considered a refractive procedure and used to reduce preexisting refractive errors. Phacoemulsification has become a routine procedure for cataract removal in most parts of the world. To obtain the advantages of a self-sealing sutureless incision at a low cost, ophthalmologists in the developing world are performing manual small-incision cataract surgery (MSICS) as an alternative procedure. SICS has emerged as an alternative as it retains the advantages of phacoemulsification and can be delivered at a lower cost in high-volume cataract surgery programs.^[4]

Wound construction plays a major role in MSICS, which may be more important than its role in phacoemulsification, where the size and shape and type of the wound remain the same in most cases. In MSICS, everything about the wound has to be carefully planned depending on the type of technique, hardness of the nucleus, amount of astigmatism, and the condition of the endothelium.^[5]

In 1990, Michael McFarland developed a sutureless incision,^[6] and Pallin^[7],[8] described a Chevron-shaped incision. During the same period, Haldipurkar SS^[6] popularized the frown incision. Recent progress in cataract surgery has increased patients' expectations and having a good postoperative uncorrected vision is considered a norm. The reduction of postoperative astigmatism is the key in meeting these expectations. The concept of surgically induced astigmatism (SIA) has added a new dimension to cataract surgery, with the emphasis more focused on the refractive aspect of surgery in the present day.

Hence, the need is to study better incision among the straight and frown to minimize postoperative astigmatism. With this background, the present study was carried out to compare SIA following straight and frown scleral incision in MSICS, to compare preoperative and postoperative keratometry readings (Kv and Kh) following straight and frown scleral incision in MSICS, and to compare refraction reading at 6^th-week postoperatively following straight and frown scleral incision in MSICS.

Materials and Methods

A hospital-based prospective study was carried out among 58 cataract patients coming to the Department of Ophthalmology, KIMS, Hubli, between the age group of 20–80 years during the study period were included in the study carried out at Karnataka Institute of Medical Sciences, Hubli, from December 2019 to November 2020.

Patients willing to give informed consent, the age group of 20–80 years having cataracts, patients with preoperative stigmatism <1 diopter, and patients with no other cause of defective vision other than cataracts were included in the present study. Patients with ocular infections, inflammations, trauma, and congenital anomaly of the eye, patients with a history of previous ocular surgeries (trabeculectomy, retinal detachment surgery, etc.), patients with any retinal pathologies, glaucoma, pseudoexfoliation syndromes, diseases of the posterior segment of the eye, and any other ocular morbidity that causes subnormal vision, and patients with preoperative astigmatism of >1 diopter were excluded from the present study.

The sample size for comparing 2 means formula was used with confidence interval (2-sided) – 95% (alpha error of 5%) and power – 80% (beta error of 20%) with Group 1 mean of 1.26 ± 0.442 and Group 2 mean of 0.97 ± 0.333. The sample size was estimated using the mean SIA measured by keratometry in the eyes following MSICS in straight and frown incisions in a study conducted by Bhumbla et al.^[11] 58 minimum sample size in Group 1 (straight incision) – 29 and minimum sample size in Group 2 (frown incision) – 29 and hence minimum total sample size – 58.

Patients between the age group of 20–80 years undergoing MSICS with intraocular lens implantation in the Department of Ophthalmology, KIMS, Hubli, from December 2019 to December 2020 were selected and randomly allotted to two groups, by alternating patients into straight and frown incision groups (FIG). Patients were enrolled for the study after noting their history and obtaining informed consent. A complete ophthalmic evaluation was done, including visual acuity (uncorrected and best-corrected visual acuity [BCVA]), preoperative retinoscopy, and anterior segment examination using a slit lamp, which includes nuclear sclerosis grading of cataract, lacrimal sac syringing, tonometry with Goldmann's applanation tonometry, keratometry (Kv and Kh), and A-scan biometry. All patients underwent systemic evaluation. Physical fitness for surgery was obtained. All patients undergoing surgery received topical antibiotics and nonsteroidal anti-inflammatory drugs instilled hourly until surgery.

Patients underwent cataract surgery by MSICS technique. The intraocular lenses made of single-piece polymethyl methacrylate were used. The patients were advised tapering a dose of antibiotic steroid combination eye drops for 6 weeks postoperatively.

Postoperative evaluation was done on the 1^st postoperative day, at the end of the 1^st week and 6^th week. SIA was calculated by subtracting the postoperative stigmatism values from the preoperative values. On each follow-up, visual acuity, slit-lamp examination, and keratometry readings were done. Retinoscopy was done at the end of 6 weeks, and BCVA was assessed.

Data were analyzed using IBM SPSS Statistics for Windows, Version 22.0. Armonk, NY: IBM Corp. IBM Corp. Released 2015. Analyzed data were presented in suitable tabular and graphical forms. Data were expressed as percentages for qualitative data. The mean and standard deviation (SD) were used for quantitative data. The Chi-square test was used as a test of significance for comparing qualitative data (gender, diagnosis, side of eye, visual acuity, and astigmatism). An unpaired t-test was used as a test of significance for comparing quantitative data (age and SIA). P <0.05 was considered statistically significant.

Results

There was no statistically significant difference in age between the two groups. There was no significant difference in gender among both groups, which showed that cataract does not show gender predilection. Laterality was insignificant. There was no statistically significant difference in diagnosis among both groups [Table 1].

Table 1: Distribution of the study participants based on sociodemographic and clinical characteristics

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There was a significant difference in the type of preoperative astigmatism in both groups. The majority of the patients had with-the-rule (WTR) astigmatism in the straight group, while the majority had against-the-rule (ATR) astigmatism in the FIG [Table 2].

Table 2: Comparison of preoperative findings in scleral incision and frown incision groups

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SIA was significantly more in the straight scleral incision group compared to the frown scleral incision group on day 1, week 1, and week 7 postoperatively [Table 3].

Table 3: Comparison of surgically induced astigmatism in scleral incision and frown incision groups

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There was no significant differences related to post-operative visual acuity (6/9) in straight scleral incision group and frown scleral incision group [Table 4].

Table 4: Comparison of postoperative visual acuity (6/9) in straight scleral incision group and frown scleral incision group

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There was a statistically significant difference in the type of postoperative (week 7) astigmatism in both groups. The straight scleral incision group had higher ATR and the frown group had higher WTR [Table 5].

Table 5: Comparison of astigmatism postoperative week 6 in the scleral incision and frown incision groups postoperative week 7

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Discussion

The straight incision group (SIG) consisted of 29 patients with a mean age group of 65.34 ± 9.13 years (mean ± SD). The FIG consisted of 29 patients as well, and the mean age group was 64.14 ± 6.02 years (mean + SD). Most of our patients belonged to the age group of 51–70 years.

Out of 29 patients in the SIG, 17 (58.6%) were female patients and 12 (41.4%) were male patients. Out of 29 patients in the FIG, 12 (41.4%) were female patients and 17 (58.6%) were male patients. Cataractous changes do not have sexual predilections. Among the 29 patients in the SIG, 1 (3.4%) had posterior polar cataract, 5 (17.2%) has posterior subcapsular cataract, 17 (58.6%) had senile immature cataract, and 6 (20.7%) had senile mature cataract. Among the 29 patients in the FIG, 4 (13.8%) has posterior subcapsular cataracts, 20 (69.0%) had senile immature cataracts, and 5 (17.2%) had senile mature cataracts.

In the SIG, 14 (48.3%) patients were operated on the left eye and 15 (51.7%) patients were operated on the right eye. In the FIG, 15 (51.7%) were operated on the left eye and 14 (48.3%) patients were operated on the right eye.

Among the patients in SIG, 9 (30.9%) patients had preoperative vision ranging between 6/24 and 6/60. Fifteen (51.7%) patients had reoperative vision between counting fingers ½ m–counting fingers 3 m. Three (10.3%) patients had a vision of hand movements with accurate projection of rays. Two (6.9%) patients had vision of light perception with accurate projection of rays. Among the patients in the FIG, 11 (37.9%) patients had preoperative vision ranging between 6/24 and 6/60. Fifteen (51.7%) patients had reoperative vision between counting fingers ½ m–counting fingers 3 m. One (3.4%) patient had a vision of hand movements with accurate projection of rays. Two (6.9%) patients had vision of light perception with accurate projection of rays.

Preoperative astigmatism was measured in all the patients. In the SIG, 17 (58.6%) patients had WTR astigmatism. Ten (34.5%) patients had ATR astigmatism. Two (6.9%) patients did not have astigmatism.

In the FIG, 6 (20.7%) patients had WTR astigmatism. Seventeen (58.6%) patients had ATR of astigmatism. Six (20.7%) patients did not have astigmatism.

All the patients underwent MSICS under peribulbar anesthesia, with straight scleral incision in 29 patients and frown scleral incision in 29 patients. Posterior chamber intraocular lens was implanted in all patients, the power of which was calculated preoperatively with the help of Bausch and Lomb keratometer, and A-scan postoperative astigmatism was studied using Bausch and Lomb keratometer.

SIA was calculated using the subtraction method (preoperative corneal astigmatism–postoperative corneal astigmatism). SIA on – Postoperative day 1 in the SIG was 1.4914D + 1.251 (mean + SD) and in the FIG was 0.629D + 0.288 (mean + SD) – Postoperative week 1 in the SIG was 0.9655D + 0.699 (mean + SD) and in the FIG was 0.474D + 0.397 (mean + SD) – Postoperative week 6 in the SIG was 0.8793D + 0.599 (mean + SD) and in the FIG was 0.414D + 0.286 (mean + SD). According to the study, the SIA was significantly more in the SIG when compared to the FIG.

Immediate and late postoperative uncorrected visual acuity was better in the FIG when compared to the SIG. On postoperative week 6, the SIG showed more ATR astigmatism, while the FIG showed more WTR astigmatism, which is more favorable to the patient. In a prospective study conducted by Jauhari et al.^[9] in Vivekananda Polyclinic and Institute of Medical Sciences, Lucknow, 75 patients aged 40 years and above with uncomplicated senile cataracts till Grade 4 nuclear sclerosis were operated on and studied. The study found that 89.5% of patients in the SIG, 94.2% in the FIG, and 95.7% in the inverted V group attained BCVA postoperatively in the range of 6/6–6/18. The mean SIA was minimum (−0.88 ± 0.61D × 90°) with inverted V incision, which was statistically significant. 11 A study conducted by Bhumbla et al. on 50 eyes (25 in SIG and 25 in FIG), the straight group had a mean SIA of 1.14 ± 0.33 D at 1 week, 1.26 ± 0.44 D at 1 month, and 1.29 ± 0.36 D at 3 months while frown group SIA was 0.94 ± 0.33 D at 1 week, 0.97 ± 0.333 at 1 month, and 0.95 ± 0.41 D at 3 months. The frown group had significantly less SIA compared to the straight group. 11

A study was conducted by Sarvarian et al.^[10] where cataract surgery was performed using a frown scleral incision. SIA was as follows − 1 week − 0.27 + 0.88 D, 1 month 0.06 + 0.82 D, 3^rd month 0.03 + 0.85 D. Bhumbla et al.^[11] found that in frown incision, the end of the incision is placed further superiorly in the sclera, it makes the incision even more stable. The ends support the inferior edge and prevent against-the-rule astigmatism. Vass et al.^[12] compared the corneal topographic changes, in the straight and FIG. The upper peripheral corneal flattening at 1 week and 1 and 3 months postoperatively was 0.7, 0.7, and 0.7 D, respectively, in the straight-incision group and 0.7, 0.4, and 0.3 D, respectively, in the FIG.

A study conducted by Reddy et al.^[13] showed that there is a significant shift to against-the-rule astigmatism with straight incision corneoscleral tunnel.

Amedo et al.^[14] conducted a study on 60 patients comparing postoperative astigmatism in straight versus frown incisions, here the FIG showed residual corneal astigmatism (RCA) values that were approximately twice as high as that recorded for the SIG; RCA at the 12^th week and beyond was 1.00 ± 0.12 D for the FIG, whereas that for the SIG was 0.50 ± 0.12 D63.

Conclusion

SIA is commonly seen in almost all patients who undergo MSICS. Postoperative emmetropia is expected by almost all the patients in the present-day scenario. Giving a good postoperative vision with minimal or no SIA depends on the operating surgeon. The placement of the scleral incision in terms of size, shape, and location plays a major role in minimizing postoperative astigmatism. The study conducted by us clearly shows that in suture less SICS frown incision produces less SIA when compared to the straight scleral incision. Our study also shows better visual rehabilitation and better uncorrected visual acuity in the FIG than in the SIG. Hence, if the operating surgeon makes minimal modification while placing the scleral incision with respect to the location and also uses the frown incision without using sutures, the patient will enjoy a good uncorrected visual acuity postoperatively.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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