|Year : 2013 | Volume
| Issue : 2 | Page : 67-72
Evaluation and comparison of surgically induced astigmatism between phacoemulsification and small incision cataract surgery
Pallavi Patil, Abhay Lune, OK Radhakrishnan, Renu Magdum, Neha Rajappa
Department of Ophthalmology, Dr. D. Y. Patil Medical College and Hospital, Pune, Maharashtra, India
|Date of Web Publication||10-Jan-2014|
Plot no. 303, Sector 24, Pradhikaran, Nigdi, Pune - 411 044. Maharashtra
Background: Surgically induced astigmatism is the cause of poor postoperative vision even after uneventful cataract surgery. Aim: The aim of study was to compare the incidence, amount, type, and course of surgically induced astigmatism and visual acuity in temporal 5.5-mm clear corneal phacoemulsification and 6-mm superior scleral incision in Small incision cataract surgery (SICS). Materials and Methods: A total of 200 eyes of 200 patients with a mean age of 62 years were included in the study. Cases were randomly divided into two groups. Group A had undergone 5.5-mm temporal clear corneal phacoemulsification and group B had undergone 6-mm superior scleral SICS. Surgically induced astigmatism was analyzed by SIA software. Results: Mean age in group A was 61 (±8) years and in group B was 63 (±10) years. Mean surgically induced astigmatism in group A was 1.05 (±0.58) D, 1.13 (±0.52) D, 1.13 (±0.56) D, and 1.08 (±0.52) D on 1 st , 7 th , 21 st , and 45 th postoperative days, respectively. The change from 1 st to 45 th day was not significant. The same in group B was 0.75 (±0.58) D, 0.81 (±0.54) D, 0.88 (±0.49) D, and 0.91 (±0.47) D on 1 st , 7 th , 21 st , and 45 th postoperative days, respectively. Surgically induced astigmatism was comparable on all days between the groups. We found significant with the rule and against the rule type of astigmatism post-operatively in the temporal clear corneal incision in phacoemulsification group and in superior scleral incision in small incision cataract surgery group respectively. Conclusion: Surgically induced astigmatism was higher in the 5.5-mm temporal clear corneal group than in the superior scleral group. Clinical outcome of both surgeries was same, as there was no significant difference in the uncorrected postoperative visual acuity in between the groups.
Keywords: Cataract surgery, superior scleral incision, surgically induced astigmatism, 5.5-mm temporal clear corneal incision
|How to cite this article:|
Patil P, Lune A, Radhakrishnan O K, Magdum R, Rajappa N. Evaluation and comparison of surgically induced astigmatism between phacoemulsification and small incision cataract surgery. Sudanese J Ophthalmol 2013;5:67-72
|How to cite this URL:|
Patil P, Lune A, Radhakrishnan O K, Magdum R, Rajappa N. Evaluation and comparison of surgically induced astigmatism between phacoemulsification and small incision cataract surgery. Sudanese J Ophthalmol [serial online] 2013 [cited 2019 May 21];5:67-72. Available from: http://www.sjopthal.net/text.asp?2013/5/2/67/124829
| Introduction|| |
Cataract is the most important and significant cause of bilateral blindness in senile age group, both in India as well as on a global scale. Modern cataract surgeries with intraocular lens (IOL) have become one of the safest, most successful, simple, and consistent, and are the most frequently performed surgeries. Small incision cataract surgery (SICS) is gaining popularity in developing countries as an inexpensive alternative to phacoemulsification.  SICS and phacoemulsification have advantages like early visual rehabilitation, less induced astigmatism, and no suture-related complications as wound construction and closure is gaining attention and importance. With astonishing advances in technology and predictability of surgery, expectations of both surgeons and patients have increased. Surgeons aim to meet the individual patient's refractive goal and patients expect good vision without the spectacles immediately.
Surprises in refractive errors after cataract surgery have become unacceptable in recent few years. As a result, cataract surgery has become refractive surgery offering improvements both in "best corrected" and "uncorrected" visual acuity. One aspect which has confounded the cataract surgeons is the postoperative induced astigmatism.  Surgically induced astigmatism (SIA) calculates the magnitude and axis of postoperative induced astigmatism by various methods introduced by Alpins and Goggin,  Holladay et al.,  and many others. Postoperative astigmatism is affected by various factors such as preoperative astigmatism, location, type, size, closure, and healing of the surgical incision, amount of scleral cauterization performed, type of suturing material used and its placement, position of IOL, and postoperative use of steroids, and all these have effects on corneal curvature.  In 1975, Jaffe and Clayman were first to report surgically induced astigmatism after cataract surgery. In 1975, Jaffe and Clayman first reported the exact measure of change induced by surgery, the SIA.  Now MS Excel sheet-based programs are available that calculate SIA. One such program was used in our study to determine SIA. It used the vector analysis with trigonometry formulas to calculate the SIA. They are also used to predict and modify the surgical skills to reduce SIA according to individuals. 
The aim of our study was to document the changes in corneal curvature occurring after cataract extraction over a period of 45 days postoperatively. We planned to compare SIA produced by 5.55-mm temporal clear corneal phacoemulsification and by 6-mm superior scleral incision in SICS. According to our literature search, very few surgeons perform 5.5-mm self-sealing temporal clear corneal surgeries, and a single documentation is available of the same.
| Materials and Methods|| |
This was a prospective, interventional, observational, follow-up study carried out from July 2011 to September 2013. A total of 200 eyes of 200 patients with a mean age of 63 years were included in the study. Ethical committee approval was obtained before starting the study.
The cases were randomly divided into two groups. One group (group A) had undergone phacoemulsification and the other group (group B) had undergone SICS. Informed consent was obtained from all the patients undergoing study.
The inclusion criteria were uncomplicated senile cataract, patients with preoperative astigmatism less then 3 D, good fixation, and cataracts up to grade 4 nuclear scleroses. Higher grade of nuclear scleroses was excluded to keep uniformity in the two groups and to keep the incisional architecture uniform and all posterior chamber intraocular lens PCIOLs were placed in the bag. Exclusion criteria were complicated cataracts, traumatic cataract, cataract with glaucoma, uveitis and tumor, cataract associated with pterygium, corneal opacity, the eyes which had undergone C3R or LASIK, presenile cataract, zonular dehiscence, and the eyes which had undergone previous ocular surgery like scleral tear repair, retinal detachment buckling surgery, glaucoma surgery, squint, corneal suturing also eyes which were high myopic and hypermetropic.
Preoperative assessment included visual acuity, intraocular pressure, sac syringing, and examination of anterior and posterior segments. A thorough posterior segment evaluation was done with 90 D. The grading of nucleus was performed according to Lens Opacification Classification System III (LOCS III). Keratometry was performed preoperatively and postoperatively by using Bausch and Lomb Keratometer. SRK II formula was used to calculate the IOL power.
All cases were operated under local peribulbar anesthesia or topical anesthesia. Under all aseptic precautions, 5% povidone iodine was instilled in the conjunctival cul-de-sac prior to surgery.
Group A patients underwent phacoemulsification. A 5.5-mm straight corneal groove was made in front of the vascular arcade with 15 no. blade. Corneal tunnel was dissected using a disposable crescent knife. Anterior chamber was entered with 2.8- or 3.2-mm keratome. Corneal tunnel was bi-planar and had self-sealing property. Corneal tunnel width was 3 mm. A side port was made. The nucleus was emulsified by chopping technique. The wound was extended with the keratome of 5.5 mm. A 5.25-mm optic sized polymethyl methacrylate (PMMA) IOL of appropriate power was implanted in the bag in all cases. Stromal hydration of the main incision and site port was done. Wound was checked for leakage by pressing over cornea with a blunt instrument.
Group B patients underwent SICS. A 6-mm scleral straight incision was made superiorly, 2 mm away from limbus, with 15 no. Bard Parker blade. Sclero-corneal tunnel was dissected using a crescent knife, and the tunnel width was 1 mm in clear cornea. Internal incisions were extended to 7 mm and hydrodissection or hydrodelineation was performed. Nucleus was brought in anterior chamber (AC) and delivered by visco-expression; PMMA PCIOL was implanted in the bag in all the cases.
Both groups had self-sealing incisions, which thereby prevented the need for any suture. There was no attempt made in any case to modify the pre-existing astigmatism.
Postoperative assessment was done on the 1 st , 7 th , 21 st , and 45 th days. At each visit, measurement of visual acuity, retinoscopy, anterior segment examination, fundoscopy, and keratometry were done. The course of postoperative astigmatic changes was determined by keratometry performed with a standard calibrated Bausch and Lomb keratometer. Corneal clarity, wound integrity, and PCIOL placement were carefully examined on postoperative follow-ups.
SIA was calculated by using SIA calculator version 3.1.  SIA was interpreted in magnitude [diopter (D)] and axis (degree).
Data analysis was done using the Statistical Package for the Social Science (SPSS) Version 15 for Windows. Z test was used to find significant differences in age, gender, SIA and astigmatism in the study group. Paired t-test was performed for SIA. Chi-square test was used to find the significance among postoperative visual acuity in the study groups. Wilcoxon test was used to find decay in type of astigmatism. A probability value of 0.05 was accepted as the level of statistical significance. P value of <0.05 was considered statistically significant.
| Results|| |
In this study, 200 eyes of 200 patients were included and underwent cataract surgery. They were categorized as group A: phacoemulsification with temporal clear corneal incision in 100 eyes and group B: 100 eyes underwent SICS with superior straight scleral incision. The results were analyzed and the following observations were made.
The mean age of the participants was 60.98 ± 7.83 years in group A and 62.88 ± 9.63 years in group B. There was no significant difference in the incidence of age between group A and group B. Group A had 54 female patients and 46 male patients. Group B had 49 male and 51 female patients. Both groups were comparable. There was no significant difference between the groups with respect to the laterality of the eye.
Uncorrected postoperative visual acuity was analyzed on the 45 th postoperative day. Three sub-groups were made to analyze the post-operative visual acuity. There was no statistically significant difference in the uncorrected postoperative visual acuity between the two groups. The two groups were comparable [Table 1].
|Table 1: Comparison of uncorrected postoperative visual acuity on 45th postoperative day in the study groups |
Click here to view
[Table 2]a shows comparison of 1 st postoperative day SIA to those of 7 th , 21 st , and 45 th days. SIA postoperatively showed no statistically significant differences in group A.
[Table 2]b shows comparison of 1 st postoperative day SIA in group B with 7 th , 21 st , and 45 th day SIA postoperatively. It shows no statistical significant difference on 7 th postoperative day, but there was significant difference on 21 st and 45 th postoperative days. There was statistical increase in SIA from 1 st to 45 th postoperative day.
A comparison of SIA between the two groups on 1 st , 7 th , 21 st , and 45 th days showed a statistically significant difference on all postoperative days [Table 2]c].
On comparing the two groups, there was a statistically significant difference between the preoperative and postoperative astigmatism [Table 3].
| Discussion|| |
Patients undergoing cataract surgery expect clear vision and less dependence on spectacles. To attain this goal, SIA has to be reduced. Modern cataract surgery aims at this modification. The rationale behind the present study was meager information available on SIA after 5.5-mm temporal clear corneal phacoemulsification surgery.
SIA was the main aim of this study, we also compared the groups with regard to age, sex and laterality of the eyes operated. All were statistically not significant. Astigmatism was assessed by using keratometery readings and SIA was calculated with SIA Soft Microsoft Excel sheet calculator.
On comparing the type of astigmatism postoperatively, we found a significant change to with the rule (WTR) astigmatism after temporal clear corneal incision and to against the rule (ATR) astigmatism in the superior scleral SICS. In our study, no oblique astigmatism was encountered. The difference was attributed to the distractive force of eyelid blinking on superior wound. The change in the corneal curvature is responsible for SIA and the astigmatic refractive error. Uncorrected astigmatism can cause blurred images and glare. These effects can create patient discomfort and dissatisfaction with otherwise uneventful cataract surgery. 
Length of incision and site are the two major factors affecting the induced astigmatism. We compared two sizes and sites, one for SICS 6-mm scleral incision and the other for phacoemulsification group 5.5-mm clear corneal incision.
Many studies document temporal clear corneal incision of 2.8, 3.2, and 4.0 mm, which induce very low astigmatism and are suitable for astigmatically neutral eyes and those with low preoperative WTR astigmatism. So, horizontal meridian incisions have an advantage of less SIA as they are away from the visual axis. ,,,,
Mahumad Asif et al. performed a study on 50 eyes. Corneal astigmatism in 5.5-mm temporal clear corneal incision that was calculated in 4 th postoperative week was 1.737 (±0.344), 8 th postoperative week was 1.739 (±0.344), and in 12 th postoperative week was 1.732 (±0.344). In comparison to the preoperative astigmatism 2.028 (±0.342), it was statistically significant.  In our study, SIA on 1 st , 7 th , 21 st , and 45 th postoperative days was as follows: 1.05 (±0.58), 1.13 (±0.52), 1.13 (±0.56), and 1.08 (±0.52). There was a steady increase in the SIA from 1 st to 7 th postoperative day; then it remained steady till 21 st postoperative day and again there was mild decrease on 45 th postoperative day, with no statistically significant difference between the SIA from 1 st to 45 th postoperative day, suggesting that wound healing and stability in this group was slow and steady.
In other studies where 5.2-mm temporal clear corneal incision was performed, all the results showed WTR-induced change in astigmatism. There was no significant refractive change in the clear corneal incision and all were comparable to the similar-sized superior clear corneal incisions. ,,
Kohnen et al. reported SIA by vector method in 20 eyes with a temporal 5.0-mm clear corneal incision, which was 0.91 (±0.77) D and 0.70 (±0.50) D SIA after 1 week and 6 months postoperatively. There was a steady decrease of SIA till 6 months postoperatively. They had used computerized videokeratographic analysis preoperatively and postoperatively. 
Bhasker et al. reported a study of 16 eyes with 6-mm superior scleral incision SICS. SIA was calculated by subtraction method and observed on 1 st , 7 th , 30 th , and 90 th postoperative days and was found to be 1.89 (±0.33) D, 1.73 (±0.38) D, 1.78 (±0.49) D, and 1.92 (±0.53) D, respectively. The study concluded that there was ATR astigmatism with the superior scleral incision.  In our study, 1 st , 7 th , 21 st , and 45 th postoperative days had 0.75 (±0.58) D, 0.81 (±0.54) D, 0.88 (±0.49) D, and 0.91 (±0.47) D SIA, respectively. On comparing the 1 st postoperative SIA with SIA of rest of the postoperative days, there was statistically significant difference on the 21 st and 45 th postoperative days and a gradual increase in SIA was seen. This suggested that the wound healing was fast and was stabilizing till the 45 th postoperative day.
Wirbelauer et al. compared 6-mm scleral incision which was placed superiorly, between "9 o'clock and 12 o'clock" (BENT = Between Nine and Twelve), and temporally. A less SIA and more rapid stabilization of the horizontal meridian were reported. BENT was effective in reducing oblique astigmatism by placing the incision on the steeper meridian. 
Malik et al. compared superior sclera incision to temporal sclera incision in SICS. They reported a mean SIA of 1.45 (±0.7387) D in a superior incisional SICS.  Ranier and associates documented ATR astigmatism of 0.41 D between postoperative day 1 and 4.4 years with a superior 4-mm scleral incision. 
Nielsen reported that self-sealing scleral incisions between 3.5 and 5.2 mm were almost astigmatically neutral and had no major astigmatism difference between them. Also, the same sized clear corneal incision had significant change in astigmatism (more with 5.2 mm). But clear corneal incisions have advantages such as speed of surgery, sparing of conjunctiva, excellent visualization, and lack of bleeding.  By subtraction method, postoperative astigmatism in group A was 0.76 (±0.44) D and in group B was 1.37 (±0.6) D, and on comparing both the groups, there was statistically significant difference.
Postoperative visual acuity was monitored on all postoperative day follow-ups in both groups, and the results were analyzed on the 45 th postoperative day. Both the groups had similar visual acuity. There was no significant difference between the two groups. This was supported by the difference of SIA in the two groups on the 45 th postoperative day. Difference in SIA was statistically significant, but there was a negligible difference between the two groups. SIA in group A was 1.08 (±0.52) and in group B was 0.91 (±0.47) on the 45 th postoperative day.
Our study is amongst the rare ones where 5.5-mm temporal clear corneal incision was analyzed. Further studies are required to find its efficacy and advantages over other types of incisions, both in SICS and phacoemulsification. Follow-up time was too short (45 days) and a longer follow-up is needed for the observation of changes in astigmatism and decay in the induced astigmatism over time as the wound heals. Videokerotography was not performed.
After an extensive literature search we could not find a self sealing 5.5 mm temporal clear corneal incision technique used in past for phacoemulsification. So we had to compare our data with an article from a non indexed journal article. Our study has proved that 5.5 mm clear corneal phacoemulsification can be done in setups where foldable lens are not available and it gives same clinical out come as a SICS surgery. Effectivity of 5.5 mm clear corneal incision with 3.2 or 3.8 mm clear corneal phacoemulsification with foldable IOL has to be further evaluated.
Due to the limitation of the resource availability and patient's affordability, we resorted to larger self-sealing incisions for implantation of rigid PMMA lens in phacoemulsification and SICS. Temporal clear corneal incision caused a minimal change in the type of astigmatism and superior scleral incision induced a significant ATR astigmatism postoperatively. Time-proven scleral incision has again stood better against the test with phacoemulsification mathematically. SIA in phacoemulsification group was slightly higher than SICS group. But the clinical evaluation proved that postoperative uncorrected visual outcome was same in both the groups. Clinically it has proved that the results of both 5.5-mm temporal clear corneal incision and 6-mm scleral incision are comparable and either of the incisions can be used while performing successful cataract surgery.
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[Table 1], [Table 2], [Table 3]