Cataract is the leading cause of avoidable blindness worldwide, responsible for nearly 51% of global blindness, as per the World Health Organization (1). Cataract surgery is therefore the most frequently performed ophthalmic operation globally, and improving visual and refractive outcomes remains a major goal of modern cataract management (2). In developed nations, phacoemulsification with foldable intraocular lens (IOL) implantation has become the standard of care. However, in developing countries, including India, manual Small Incision Cataract Surgery (SICS) continues to be widely used because of its cost-effectiveness, shorter operative time, minimal instrumentation requirements, and comparable outcomes (3).

A crucial determinant of postoperative uncorrected visual acuity following cataract surgery is surgically induced astigmatism (SIA). SIA occurs due to corneal shape alteration from the surgical incision and wound healing process, leading to corneal flattening or steepening along specific meridians (4). Factors such as incision size, shape, location, and construction, as well as pre-existing corneal curvature, play a significant role in the magnitude and direction of astigmatic change (5). Traditionally, the incision in SICS is placed in the superior scleral region beneath the upper eyelid. This offers better wound protection and cosmesis but is often associated with against-the-rule (ATR) astigmatism, as superior incisions flatten the vertical meridian of the cornea (6). To overcome this, temporal SICS has emerged as a viable alternative. Temporal incisions induce less astigmatism, are closer to the optical axis, and provide faster visual recovery and more stable postoperative refractive outcomes (7).

Worldwide, numerous studies have compared incision locations in cataract surgery to minimize postoperative astigmatism. Research from countries like Japan, the United Kingdom, and the United States has consistently shown that temporal incisions cause less surgically induced astigmatism compared to superior or supertemporal approaches (4,6). The temporal approach also reduces the effect of eyelid pressure and gravitational force on the corneal wound, providing a more stable refractive outcome, particularly in elderly patients who often have pre-existing ATR astigmatism. In India, where cataract accounts for more than 60% of visual impairment, SICS remains the most commonly performed procedure in both rural outreach and tertiary eye care centres (2,3). Studies from Indian institutions have highlighted that temporal SICS not only results in lesser SIA but also ensures faster visual rehabilitation, making it a preferred approach in high-volume cataract surgery programs (7). However, superior SICS is still widely practiced due to surgeon familiarity and ease of approach. Comparing these two techniques in the Indian population is essential to establish evidence-based surgical preferences tailored to patient needs and anatomical factors such as palpebral fissure height and head positioning during surgery.

Hence, this study aims to compare the surgically induced astigmatism between superior and temporal SICS, thereby determining the incision site that offers the best refractive stability and visual outcome in routine cataract surgery.

Aim and Objectives

Aim

To compare the surgically induced astigmatism (SIA) between superior and temporal approaches of small incision cataract surgery (SICS).

Objectives

1. To measure and compare the magnitude and axis of surgically induced astigmatism following superior and temporal SICS.
2. To evaluate the postoperative visual outcomes in both groups.
3. To determine which incision site provides better refractive stability and faster visual rehabilitation.

Study Design and Setting

This was a prospective, comparative, interventional study conducted in the Department of Ophthalmology at over a period of 12 months. Patients diagnosed with age-related cataract and planned for manual small incision cataract surgery (SICS) were enrolled. The study compared postoperative astigmatic outcomes between superior SICS and temporal SICS.

Study Population

A total of 100 patients (100 eyes) were included and randomly divided into two groups:

• Group A (Superior SICS) – 50 patients
• Group B (Temporal SICS) – 50 patients

Only one eye per patient was included to avoid correlation bias.

Inclusion Criteria

• Patients aged 40–80 years.
• Diagnosed cases of senile (age-related) cataract.
• Patients willing to undergo SICS and provide informed consent.
• Regular corneal astigmatism ≤ 2.0 D preoperatively.
• Clear cornea permitting keratometric readings.

Exclusion Criteria

• Previous ocular surgery or trauma.
• Corneal pathologies (opacity, ectasia, irregular astigmatism).
• Pseudoexfoliation, zonular weakness, or subluxated lens.
• Preoperative astigmatism > 2.0 D.
• Glaucoma or optic nerve abnormalities.
• Intraoperative complications (PCR, vitreous loss).
• Uncontrolled diabetes or hypertension.

Preoperative Assessment

1. Visual Acuity

• Uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA) were recorded using Snellen’s chart.

2. Slit-Lamp Examination

• To assess cataract grade, corneal clarity, and anterior segment status.

3. Keratometry

• Performed using an autorefractokeratometer or manual keratometer.
• Both K1 (flat meridian) and K2 (steep meridian) values were recorded.
• The axis and magnitude of preoperative astigmatism were documented.

4. Intraocular Pressure

• Measured with Goldmann applanation tonometry.

5. Fundus Examination

• Using indirect ophthalmoscopy.
• B-scan ultrasound for dense cataracts.

6. Biometry

• Axial length and IOL power calculation using SRK-II or SRK/T formula as appropriate.

Randomization

Patients were randomly allocated to either the superior or temporal SICS groups using a simple computer-generated random table.

Surgical Technique

Common Steps for Both Groups

All surgeries were performed by the same experienced surgeon to avoid inter-surgeon variability.

• Peribulbar anesthesia was used.
• Fornix-based conjunctival flap was created at the incision site.
• A self-sealing, scleral tunnel was constructed using a 15° blade and crescent knife.
• Side-port incision on opposite meridian.
• Hydrodissection and nucleus delivery using viscoexpression or irrigating vectis.
• Cortical aspiration using Simcoe cannula.
• Rigid PMMA posterior chamber IOL (6 mm optic) implantation.
• Tunnel integrity checked using Weck-cel sponge.
• Conjunctiva reposited without sutures.

Group A – Superior SICS

• Incision placed at 12 o’clock position.
• Scleral tunnel size: 6.5–7.0 mm, 2 mm posterior to limbus.

Group B – Temporal SICS

• Incision placed at 3 o’clock (right eye) or 9 o’clock (left eye).
• Scleral tunnel size identical to superior.
• Head was rotated slightly to improve exposure if needed.

Postoperative Management

• Topical antibiotic-steroid drops (6 weeks taper).
• Lubricants as needed.
• Follow-up on: Day 1, Week 1, Week 4, and Week 6.

Postoperative Assessment

Visual Acuity

• UCVA and BCVA recorded at each visit.

Keratometry

• Performed at Week 1, Week 4, and Week 6.
• Final analysis based on 6-week keratometry, once corneal healing stabilized.

Calculation of Surgically Induced Astigmatism (SIA)

SIA was calculated using:

• Alpins Vector Method (preferred),
  OR
• SIA Calculator (Holladay) — if vector analysis tools unavailable.

Parameters analyzed:

• Change in flat (K1) and steep (K2) meridian
• Axis shift
• Net astigmatism changes in diopters

Outcome Measures

1. Primary outcome: Magnitude of SIA at 6 weeks
2. Secondary outcomes:
• Axis of induced astigmatism
• Postoperative UCVA and BCVA
• Comparison between superior and temporal groups

Statistical Analysis

• Data entered in Microsoft Excel and analyzed using SPSS.
• Continuous variables: mean ± standard deviation (SD).
• Comparison between groups:
• Independent t-test for SIA and keratometry values
• Chi-square test for categorical variables
• p ≤ 0.05 considered statistically significant.

A total of 100 patients (100 eyes) were included in the study — 50 underwent superior SICS (Group A) and 50 underwent temporal SICS (Group B). All patients completed follow-up for 6 weeks postoperatively.

Table 1. Demographic Profile of Patients

Observation: The two groups were comparable in age, gender, and preoperative visual acuity (p > 0.05).

Table 2. Preoperative Keratometric Readings

Observation: There was no significant difference in baseline corneal curvature or preoperative astigmatism between groups.

Table 3. Postoperative Keratometry at 6 Weeks

*p < 0.05 = statistically significant

Observation: Mean postoperative astigmatism was significantly higher in the superior SICS group.

Table 4. Comparison of Surgically Induced Astigmatism (SIA)

Observation: The average SIA was significantly greater in superior SICS (1.02 D) than in temporal SICS (0.65 D).

Table 5. Axis of Induced Astigmatism

Observation: Superior SICS predominantly caused against-the-rule (ATR) astigmatism, while temporal SICS favoured with-the-rule (WTR) pattern — difference statistically significant.

Table 6. Postoperative Visual Outcomes (at 6 weeks)

Observation: Temporal SICS provided better uncorrected visual acuity at 6 weeks, attributed to lower SIA.

Summary of Findings

• The mean surgically induced astigmatism (SIA) was significantly higher in the superior incision group (1.02 D) compared to the temporal group (0.65 D).
• Superior SICS commonly induced against-the-rule (ATR) astigmatism.
• Temporal SICS showed faster visual recovery, less SIA, and better postoperative UCVA.
• Both groups achieved excellent BCVA at final follow-up.
• The difference in postoperative astigmatism and uncorrected vision was statistically significant (p < 0.05).

This prospective comparative study was conducted to evaluate and compare surgically induced astigmatism (SIA) following superior and temporal small incision cataract surgery (SICS). The results demonstrated that the mean SIA in the superior group was 1.02 ± 0.34 D, significantly higher than that in the temporal group (0.65 ± 0.28 D, p < 0.001). In addition, temporal SICS showed a greater proportion of patients achieving uncorrected visual acuity (UCVA) ≥6/9 at 6 weeks, indicating a more stable postoperative refractive outcome. Astigmatism following cataract surgery is primarily influenced by the location, size, and configuration of the incision, as well as by wound healing forces and corneal biomechanics (8). Superior incisions are located along the vertical meridian, which is more prone to flattening due to postoperative wound healing and eyelid pressure from blinking. This often leads to against-the-rule (ATR) astigmatism. In contrast, temporal incisions, placed horizontally near the corneal equator, produce less corneal flattening and thereby induce smaller amounts of SIA (9).

The present findings corroborate this principle, as superior SICS resulted in a predominant ATR shift, whereas temporal SICS induced mild with-the-rule (WTR) astigmatism in most patients. This suggests that the incision site plays a critical role in determining the direction and magnitude of postoperative corneal curvature changes. The findings of this study align with numerous international reports. Hanna et al. (1990) and Jaffe et al. (1997) demonstrated that corneal flattening increases along the meridian of incision, producing greater SIA with superior approaches (10,11). Gills et al. (1998) and Hayashi et al. (2001) reported that temporal incisions lead to smaller changes in corneal topography and faster visual stabilization (12). Gokhale and Sawhney (2005) also observed that temporal SICS induced significantly less astigmatism (0.7 D) than superior SICS (1.1 D) at six weeks postoperatively, a finding closely matching our results (13). Similarly, Shah et al. (2009) noted that temporal approaches preserve corneal symmetry better and minimize postoperative refractive error (14). Collectively, these studies and the current results confirm that temporal incisions cause less biomechanical alteration of the cornea and are advantageous for achieving better uncorrected visual outcomes.

In India, manual SICS remains the mainstay of cataract surgery, especially in government and outreach programs due to its cost-effectiveness and minimal instrumentation. Several Indian studies have echoed the findings of the present work. Reddy et al. (2000) reported that superior SICS induced significantly more astigmatism than temporal SICS in Indian eyes, attributed to steeper vertical corneal curvature and smaller palpebral apertures (9). Gokhale et al. (2005) and Raj et al. (2004) found similar results, emphasizing that temporal incisions minimize postoperative astigmatic changes and allow for earlier visual rehabilitation, which is particularly beneficial in high-volume cataract centers (13,14). Thus, temporal SICS appears better suited for the Indian population, where pre-existing ATR astigmatism is common in elderly patients. In this study, postoperative uncorrected visual acuity (UCVA) was significantly better in the temporal group (p = 0.01). However, the best-corrected visual acuity (BCVA) was comparable between the two groups, indicating that the difference in uncorrected vision was mainly due to the magnitude of residual astigmatism. This reinforces the role of incision placement in optimizing refractive outcomes after cataract surgery. The choice of incision site should be tailored to each patient’s preoperative corneal astigmatism. For patients with pre-existing WTR astigmatism, a superior incision may be advantageous to reduce it, while those with ATR astigmatism may benefit more from a temporal incision to prevent further flattening of the vertical meridian. Temporal SICS also offers additional advantages such as better wound exposure, minimal induced astigmatism, early visual recovery, and reduced surgical time. However, in deep-set eyes or patients with narrow palpebral fissures, a superior approach may still be technically easier.

This study demonstrated that temporal small incision cataract surgery (SICS) induces significantly less postoperative astigmatism compared to the superior approach. Temporal incisions produced smaller surgically induced astigmatism (SIA), better uncorrected visual acuity, and faster visual rehabilitation. Superior incisions tended to cause against-the-rule (ATR) astigmatism, while temporal incisions maintained more favorable corneal curvature. Given these findings, temporal SICS can be considered the preferred incision site for minimizing astigmatism and achieving optimal postoperative refractive outcomes, particularly in patients with pre-existing ATR astigmatism.

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