Introduction

Cataract is the most common cause of blindness in world. In India, it is responsible for 62.60% cases of blindness.1 Thus, by the current Indian definition of blindness there are over 12 million people blind due to cataract in India.2 Our current knowledge of the disease indicates that there is no effective medicinal treatment the only curative treatment for cataract being surgery.3 Although cataract surgery has been performed since ancient times, the last half century has seen remarkable refinements of the procedure. The modern cataract surgery aims at earliest visual rehabilitation in a minimal invasive manner. Today cataract surgery is also being considered a form of refractive surgery offering improvements in both best corrected and uncorrected visual acuity. Corneal astigmatism or surgically induced astigmatism has been a by^-product of cataract surgery since the first limbal incision was made. Surgically induced astigmatism is a big deterrent to ophthalmologists aim of making his patients emmetropic because it is an integral part of the postoperative refractive error. Currently majority of cataract surgeries are either small incision cataract surgery or phacoemulsification. Phacoemulsification has become the biggest surgical achievement of the present decade; it is still not practised by a majority of surgeons in developing countries and not feasible for mass surgeries as practised in India. Thus, it is important to study the post operative astigmatism in both types of surgeries so that we can modify the causative factors. That will help in obtaining a more rapid visual rehabilitation, greater patient satisfaction and better optical results along with quality of vision. In fact, today the emphasis is not only on eliminating or minimising surgically induced astigmatism but also neutralising any pre-existing astigmatism. Previous many studies have compared SIA in manual small incision cataract surgery with temporal versus superior incision. Similarly, there are studies about SIA comparing incision sites in phacoemulsification. Also, comparing various sizes of incision and induced astigmatism. This study is designed to study to compare astigmatism (SIA) induced after manual small incision cataract surgery and phacoemulsification at tertiary health care centre, Rajkot, Gujarat.

Materials and Methods

The study was carried out in Department of Ophthalmology at Tertiary health centre Rajkot with due knowledge and permission of operating surgeons and patients operated in the duration of 24 months from September 2020 to October 2022.

Informed consent was obtained from all the patients undergoing study. It was a prospective study and all the patients were randomly selected over the above-mentioned period that had cataract with normal anterior and posterior segments. To have a more homogeneous study population all the patients underwent a similar Preoperative, Intra operative, Postoperative Surgical protocols.

All eyes were operated under peribulbar anaesthesia with 2% lignocaine+bupivacain+hyalronidase. A Superior sclero corneal pocket tunnel with external incision of frown and straight configuration in manual SICS and straight incision in phacoemulsification was made. In all the cases incision of size 3.2 mm was used in phacoemulsification and incision of size 6.5 mm was used in manual SICS.

Patients with any other ocular disease or any prior surgery of eye other than cataract, patients in whom any intra operative complication occurred, patients with any wound related problems and patients in whom sutures were taken on wound postoperatively were excluded from the study.

Through exclusion criteria, 500 patients were selected which were grouped into:

Group 1 of 250 patients cataract surgery. Who underwent manual small incision cataract surgery. Group II of 250 patients who underwent phacoemulsification surgery.

Vector analysis method

Here we find the sum of oblique cylinders in which the cylinder is represented on a graph by vector. The vectors representing the cylindric powers are directed at angles twice the actual angles of orientation before the eye and the final axis is divided by two.e.g. K1 (preop corneal astigmatism) = 2.00 x 25°.

K3 (postop cornel astigmatism) =1.50 x 85.

K1 is represented on a graph as a line 2 unit long at 50-degree meridian K3 is plotted as a line 1.50 unit long at the 170-degree meridian. The parallelogram is completed. Line K2 (resultant) is 1,75 units long at 98 degrees. Thus, SIA is 1.75 D x 49. We can modify this technique by construction of a triangle also.

Figure 0

Rectangular coordinates. Any point may be represented on a graph by rectangular and polar coordinates. The rectangular coordinates of K2 are thus calculated by subtracting the x and y coordinates from K1 from those of K3

Thus K2=K3-K1 = (xK3-xK1, yK3-yK1)

Other methods for calculating SIA are: -

1. Law of sines and cosines

2. Vector decomposition

3. Cravys vertical vectors

4. Naesers Polar Values

5. Algebraic method

6. The double angle vector diagram

Online calculators: Two popular online SIA calculators are available at http://doctor-hill.com/physicians/ download.htm (East Valley Ophthalmology, Arizona) and (http://www.insighteyeclinic.in/SIA_calculator.php. Both of these free online calculators use the method of SIA calculation described by Holladay et al.

Results

Table 1 thus shows that in this study, 51.4% patients were males and 48.6% were females. Among 500 cases, 57.2% Right eye and 42.8% Left eye were operated.

Table 2 show that maximum patients i.e., 35.6% were in age group 51 to 60 years. Least number of patients were in age group above 80 years i.e., 3.4%.

Table 3 shows that in maximum patients (51.8%) there was low pre operative astigmatism (<1D). The range of astigmatism was 0 to 4D in group 1 and the range of astigmatism was 0 to 2.5D in group 2. The average pre operative astigmatism in group 1 is 1.1 in group 1 and in group 2 is 0.84.

Cases which had steep axis between 45-135 degrees were considered in WTR group and those between 0-44 or 136-180 were considered in ATR group. Table 4 shows that 73.6% cases had WTR and 26.4% cases had ATR astigmatism with nearly equal distribution in both study groups.

Table 5 shows that at the end of first postoperative month average post-operative astigmatism in group 1 was 1.04 and in group 2 was 0.90. In both groups average post-operative astigmatism was maximum on first post-operative day. This data when analyzed by students T- Test gives p value less than 0.01 implying that difference in both groups was significant.

Table 6 shows that at the end of first postoperative month average SIA in group 1 was 1.32 and in group 2 was 0.60. In both groups average SIA was maximum on first post-operative day. This data when analyzed by students T- Test gives p value less than 0.05 implying that difference in both groups was significant.

Table 7 shows that group 1 cases had more ATR astigmatism at end of 1^st post operative month (80%) as compared to group 2 cases whereas group 2 cases had more WTR astigmatism (67%).

Table 8 shows that maximum cases with post-operative astigmatism in group 1 were in sub group 1.01-1.5 dioptres at the end of 1^st post-operative month.

Table 9 shows that maximum cases with post-operative astigmatism were in sub group 0-0.5 diopters in group 2 patients at the end of 1^st post-operative month.

Table 10 shows that maximum SIA were in sub group 1.01-1.5 dioptres in group 1 patients at the end of 1^st post operative month.

Table 11 shows that maximum SIA were in sub group 0.51-1 dioptres in group 2 patients at the end of 1^st post-operative month.

Table 12 shows that in group 1 there were more cases of ATR type of SIA with average SIA of 1.1 Dioptres and in group 2 there were more cases of WTR type of SIA with average of 1.01 Dioptres at end of first post-operative month.

Table 13 shows in group 1 patients, SIA was more after straight incision as compared to the frown incision after one month 1^st post operative period.

Discussion

Average SIA in SICS in present study was 1.32 and in other studies by Hazra S, et al4 it was 1.00, D Singh et al5 it was 1.12, V Sharma et al6 it was 1.36, Bhaskar Reddy et al7 it was 1.92. Average SIA in phacoemulsification in present study was 0.60 and in other studies like Hazra S, et al. it was 0.87, D Singh et al. it was 0.77, George et al8 it was 0.77, Lhyne et al9 it was 0.61 and Bhaskar Reddy et al. it was 1.23.

On comparing SIA in SICS and phacoemulsification in present study it was found SIA was less in Phacoemulsification. SIA in SICS and phacoemulsification in present study was 1.32 and 0.60 respectively. In other studies, like by George et al. (SIA in SICS and Phacoemulsification was 1.17 and 0.77 respectively) and by Bhaskar Reddy et al (SIA in SICS and Phacoemulsification was 1.92 and 1.23 respectively) results were same as our study.

Type of SIA in SICS in present study showed 20% patient had WTR, while 80% patient had ATR which was similar to results in other studies like by R.C. Nagpal et al where 58.3% patient had WTR while 41.7% patient had ATR, and in study by D Singh et al, where 32.5% patient had WTR while 54.5% patient had ATR. Greater percentage of WTR in SICS can be attributed to the superior scleral incision (irrespective of configuration of incision) causing the flattening of the axis of incision i.e vertical axis and relative steeping of the horizontal axis.

In present study, on comparing incision configuration it was found superior scleral frown incision showed less SIA (SIA in frown incision 1.0) in comparison to superior scleral straight incision in SICS. In other studies, like by Bhaskar et al, SIA was 1.57 and 1.92 in superior scleral frown and superior scleral straight incision respectively and by D Singh et al SIA in superior scleral straight incision was 1.22 and 1.1 in superior frown scleral incision. Irrespective of the configuration of incision, SIA in SICS was higher than phacoemulsification.

On comparing size of incision, it was found SIA was higher in incision size of 6-6.5mm in SICS in comparison to 3.2mm to 3.8mm incision in phacoemulsification. Similar results were seen in study by George et al (SIA in SICS was 1.17 while in phacoemulsification it was 0.77), by Dr R.C Nagpal et al, and by D Singh et al.

SIA decreased from 1.66 D on first postoperative day to 1.32 D on first postoperative month in group I and from 0.63 D to 0.60 D in group 2. SIA was maximum on first post-operative day and it regressed with time as noted on first post-operative month in both the groups.

Post-operative astigmatism was ATR type in majority of cases Group 1 (SICS) as there was a flattening in the axis of the incision in surgeries (superior scleral site in study cases). In group II there was not much shift of astigmatic axis to ATR type which means that smaller incisions do not cause axis shift significantly. In majority of patients, average post-operative residual astigmatism was 1.04 D in group I and 0.90 D in Group II at the end of first postoperative month. All cases with tunnel complications were found to have higher astigmatism (these cases were not included in study to avoid error). If we extrapolate the regression seen in this study in post operative astigmatism in SICS, then it will be very low in amount at the end of one year.

Conclusion

Majority of cases (51.8%) had low (<1 D) pre-existing astigmatism. Only 8.4% cases had high pre-existing astigmatism (>2 D). Majority of cases (68.5%) had pre-existing astigmatism of WTR type.

Average SIA in group I (SICS) was 1.32 SD and in group II (Phacoemulsification) was 0.60 SD which was due to larger incision size in SICS in comparison to phacoemulsification.

Average post-operative residual astigmatism was 1.04 D in group I and 0.90 D in Group II at the end of first postoperative month. Post-operative astigmatism was ATR type in majority of cases Group 1 (SICS) and in group II there was not much shift of astigmatic axis to ATR type.

Superior scleral frown incision showed less SIA (SIA in frown incision 1.0) in comparison to superior scleral straight incision in SICS.

Visual outcome in both SICS and Phacoemulsification was same. Thus, SICS is a good, safe, effective and economical alternative of phacoemulsification surgery.

Abbrevations

SIA: Surgical induced astigmatism; WTR: With the rule astigmatism; ATR: Against the rule astigmatism; SICS- Small incision cataract surgery.

Ethical Approval

The study received ethical clearance from institutional ethical committee.

Source of Funding

None.

Conflict of Interest

The authors declare that they have no conflict of interest.