Comparison of Astigmatism following Manual Small Incision Cataract Surgery: (Superior versus Temporal approach)

Objective: To compare astigmatism induced by the superior and temporal section inmanual small incision cataract surgery.
Material and Method: This study was a randomized comparative trial conducted at the department of Ophthalmology, Hayatabad Medical Complex Peshawar, from May 31, 2018 to Nov 30, 2018. 164 patients were included through Out Patient
Department and informed written consent was taken. Personal biodata was recorded on predesigned proforma. Patients were randomly allocated by lottery method to superior incision group and temporal incision group. Corneal astigmatism was measured by Helm holtz keratometer (Topcon OM-4).
Results: A total of 164 patients of 50-74 years of age of either gender undergoing manual small incision cataract surgery
were studied, who were divided into two equal groups. Overall male to female ratio was 1.20:1. Sex distribution among the
groups was insignificant with p-value= 0. 376. Surgically induced astigmatism wise distribution shows that patients in superior incision group (Group A) have average astigmatism of 0.328+0.3335SD while in temporal incision group (Group B) it was 0.243+0.296SD, which was significant with p-value = 0.080.
Conclusion: Both incisions resulted in same amount of mean astigmatism at 6 weeks and difference in mean surgically induced astigmatism (SIA) was found to be statistically insignificant. Temporal incision had the trend of inducing with-therule astigmatism.
Key Words:Astigmatism; Surgically Induced Astigmatism; Manual Small Incision Cataract Surgery; Extra capsular cataract extraction; Cataract visual-outcome; Keratometry.

 

 

INTRODUCTION

Cataract remains the leading cause of avoidable blindness worldwide1, and is the most commonly performed surgical procedure in the world, with an estimated 19 million operations performed annually2. However, the safest, most effective, and economical technique of cataract surgery remains debatable. Over the past decade, manual small incision cataract surgery (MSICS) has become an established surgical alternative to phacoemulsification1.


1 Registrar / Senior Medical Officer, 2 Assistant Professor,
3  Trainee Medical Officer, 4 Medical Officer, 5 Associate Professor


Correspondence: Dr. Syed Amir Hamza, Registrar/ Senior Medical
Officer, Department of Ophthalmology, Hayatabad Medical Complex,
Peshawar. Room No. A4, Khyber Hall Hostel, HMC, Peshawar. Mob
No: 0332 9158001, Email: drsyedamirhamza@gmail.com


Both incisions resulted in same amount of mean astigmatism at 6 weeks and was found to be statistically insignificant. Temporal incision had the trend of inducing with-the-rule astigmatism.


Manual small-incision cataract surgery (MSICS) is a cost-saving procedure and is suitable for developing countries3. Now-a-days, all techniques of cataract  extraction are being modified to give best uncorrected visual acuity and early rehabilitation4. In addition to improving visual acuity (VA), one of the goals of modern cataract surgery is to reduce pre-existing astig-matism (PEA), a factor that may reduce VA and affect the quality of vision5. A variety of scleral incisions are being used in MSICS, with the aim of keeping the post operative astigmatism to a minimum6. Previous studies examined the astigmatism induced after an incision in various locations including the superior, supero-temporal, supero-nasal, temporal, and nasal7. As regards the choice of incision location, previous studies reported that superior incision induces greater corneal astigmatic change (against-the-rule astigmatism) (ATR), than temporal incision (which induces with-the-rule astigmatism) (WTR)5.. In general, patients with senile cataracts have an against-the-rule astigmatism. Surgical techniques that decrease postoperative against-therule astigmatisms have good outcomes8. A study done by Magdum RM et al showed that “In superior incision group, mean SIA was 1.09D + 0.66 and temporal incision group the mean SIA was 0.72D + 0.79 and the difference between the groups was statistically significant9. MATERIALS AND METHODS: This study was conducted at the department of ophthalmology, Hayatabad medical complex Peshawar, from May 31, 2018 to Nov 30, 2018.It was a randomized comparative trial. Sample size was based on study done by Magdum RM et al whereby mean SIA in  superior incision group was 1.09D + 0.66 and mean SIA in temporal incision group was 0.72D + 0.79, keeping power of the test 90% , the sample size in each group was 82 and total sample size was 164. Sampling technique was simple random by lottery method. Patients having age related cataract, aged 50  years or above, from either gender, well-controlled for diabetes and hypertension and without any cardiovascular disease were included in the study. Patients having corneal scarring, opacity, degeneration or dystrophy, glaucoma, pseudo-exfoliation, traumatic cataract, macular degeneration, diabetic or hypertensive retinopathy and oblique astigmatism were excluded. Patients were selected through Out Patient Department personal bio-data was taken on predesigned proforma. Corneal astigmatism was measured by Helm Holtz keratometer (Topcon OM-4) (k values were taken in diopter). They were randomly allocated to a group by lottery method. Patients were divided into two groups; Group A: MSICS with superior approach and Group B: MSICS with temporal approach. All patients were operated by one surgeon at the time of initiating this study. All surgeries were performed under peribulbar anaesthesia. In MSICS with superior approach 8mm scleral incision 1.5mm away from the limbus superiorly was given. In MSICS with temporal approach 8mm sclera incision 1.5mm away from the limbus temporally was given. Hard posterior chamber intraocular lens was used. Intracameral antibiotics were injected in all patients after the procedure. Corneal astigmatism was measured preoperatively and then at 6th week post operatively in both groups using same keratometer. Statistical analysis of data was performed using SPSS software version 20. Descriptive analysis was done using means and standard deviations for continuous variables like age and surgically induced astigmatism and iIndependent T test was applied to compare (surgically induced astigmatism) in two groups. Effect modifiers like age and gender were addressed through stratification by taking P-value <0.05 as significant.

RESULTS

A total of 164 patients of 50-74 years of age of either gender undergoing manual small incision cataract surgery were studied, who were divided into two equal groups. Patients in one group with superior incisionswas made (Group A) while patients in another group passed through temporal incision (Group B). There were 46(56.1%) male and 36(43.9%) female patients in Group A while 49(59.8%) were males and 33(40.2%) were females in Group B, which was statistically insignificant in both the groups with p-value 0.376. Overall male to female ratio is 1.20:1.



Table 1 Average age was 58.09 years+ 5.86SD in Group  A and contains 27(32.9%) patients having less than or equal to 55 years, 45(54.9%) patients 56-65 years and 10(12.2%) patients lie in the age of more than 65 years. While Group B have average age of 57.70 +6.05SD and contains 30(36.6%) patients in less than or equal to 55 years, 43(52.4%) in 56-65 years and 9(11%) patients have age more than 65 years. The overall average of the patients was 57.89 years +5.94SD. The age distribution among the groups was insignificant with p-value 0.880.



Table 2 Surgically induced astigmatism wise distribution shows that Group A have average astigmatism of 0.328+ 0.3335SD while in Group B it was 0.243+0.296SD which was significant with p-value = 0.080.



Table 3 When surgically induced astigmatism was stratified for age in both the groups, it was found that age group was insignificant for astigmatism in both the groups.



Table 4 Similarly when pain of the patients was stratified for gender, it shows that pain was significant in males while females have insignificant effect in both the groups. Table 5



DISCUSSION

Advocates of phacoemulsification and MSICS report less post-surgical astigmatism along with earlier stabilization of refraction, visual acuity andearly spectacle correction.10 MSICS technique was introduced by Ruit et al in 2000, and since then, this technique has  grown in popularity in developingcountries.12 The basic aim of this study was to compare the surgically induced astigmatism at two incision sites in manual small incision cataract surgery. Cataract surgery has transformed into a refractive surgical procedure, as incision location in cataract surgery can affect the corneal astigmatism and ultimate visual outcome. In clear corneal surgery, placement of the incision on steepaxis can help to reduce astigmatism within the meridian.11,12 In a kerato-refractive surgery it was seen that astigmatism as low as 0.75 D may leave a patient symptomatic with visual blur, ghosting and halos.13 In a study conducted on 1500 patients mean surgically inducedastigmatism in MSICS at 6 weeks postop was found to be 0.3 D,14 another study showed a SIA of 0.69 Dbut these studies did not compare SIA at different incision sites. In our study mean SIA at 6 weeks in superior incision group was 0.367 ± 0.669 D which is comparable to earlier studies. In temporal incision group mean SIAat 6 weeks was 0.225 ± 0.529 D. It can be seen here that temporal incision induced less mean SIA than superior incision but this difference was statistically insignificant (p value 0.257). A study conducted in India had found the mean SIA of 1.28 D for superior incision and 0.37 D for temporal incisionin MSICS.7 In our study it is seen that superior incision group has resulted in a higher SIA at 6 weeks. Exact cause is undetermined but it is possible that less mean pre-op astigmatism resulted in a higher SIA in this group. When only mean astigmatism present at 6 weeks was compared both groups had equal amountof astigmatism (0.892 D in superior incision group vs. 0.894 D in temporal incision group). In 2007, Ruit et.,al compared MSICS with Phacoemulsification, in their series all MSICS surgeries were performed by a temporal incision; mean astigmatism was 0.88 D which is comparableto mean astigmatism in temporal group of our study at 6 weeks.15 However, another study showed higher mean postop astigmatism in superior incision than in temporal incision, 1.45 D versus 0.43 D respectively. 7 Paired T test was applied to determine the effect of incision site on magnitude of postop astigmatism. Superior incision had an insignificant effect on magnitude of astigmatism at 6 weeks (p value 0.139) while temporal incision had a significant effect on magnitude of astigmatism at 6 weeks (p value <0.001). When both the groups were compared no significant difference in amount of pre and postop astigmatism was seen (p-value0.089 and 0.990 respectively). Both the study groups showed a significant association between incision site and change in axis of astigmatism as determined by chi-square test (P value 0.005 in superior incision group versus 0.021 in temporal incision group). In superior incision group out of 24 eyes who had pre-op with-the-rule astigmatism, 7 eyes (29.1%) retained with-the-rule astigmatism they had pre-op astigmatism equal to or more than 0.75 D. 14 eyes (58.3%) developed against-the-rule astigmatism along with 3 eyes (12.5%) with neutral astigmatism postoperatively. These 17 eyes were having pre-op astigmatism  0.5 D or less. All the 25 eyes having pre-op against-therule astigmatism, retained against-the-rule astigmatism post-operatively. Astigmatism shift was seen in those patients in superior incision group with a pre-op astigmatism of 0.5 D or less. Tejedor and Murube, in a study of patients having with-the-rule astigmatism, recommended at least 1.5 diopters of corneal astigmatism in a superior incision in order to avoid a change in axis.16 Chi-square test showed a significant relationship between incision site and axis shift in astigmatism (p value 0.005).In temporal incision group 20 eyes (100%) with pre-op with-the-rule astigmatism, retained with-the-rule astigmatism postoperatively. While 20 eyes (74%) having pre-op against-the-rule astigmatism along with 6 eyes (100%) having neutral pre-op astigmatism had a postop axis shift to with-the-rule astigmatism. Seventy three percent of patients with axis shift were having pre-op astigmatism of 0.75 D or less. In one of the study, 75% of cases who had against-the-rule astigmatism and who underwent surgery through a temporal incision for an astigmatism axis shift of 90 degrees were found to have a preoperative astigmatism magnitude of less than 0.75 diopters. 16 These results are comparable to our study and chi-square test showed a significant relationship between incision site and axis shift in astigmatism (P value 0.021). When both the groups were compared using chi-square test, a significant difference in type of postop astigmatism was noted with 81.1% of eyes in superior incision group having against-the-rule shift while 86.8% of eyes in temporal incision group having withthe- rule shift (p value 0.000) Studies have shown that if the magnitude of astigmatism is significantly reduced, the patient’s visual acuity could improve, even if axis shift occurs. However, it is generally accepted that reducing astigmatism without significantly changing the axis is well tolerated and should be the goal.17,18 There is a difference of opinion as to which type of astigmatism, if any, is preferable after cataract surgery. Some authors have suggested that residual with-the-rule astigmatism may favor better uncorrected distance acuity and is better tolerated visually,19,20 others believe that low myopic against-therule astigmatism provides better near UCVA compared to an equal amount of with- the-rule astigmatism.21 In our study 50% patients in temporal incision group had against the rule astigmatism preoperatively which reduced to 13.2 % postoperatively. Actual impact of this change could not be assessed because visual acuityassessment was not performed in this study. In a study conducted by Huang and Tseng from Taiwan, surgically induced astigmatism was compared between two groups of patients in which suture-less temporal clear corneal and suture-less temporal scleral frown incisions were given. It was concluded that scleral frown incision resulted in a much lesser amount of surgically-induced corneal astigmatism as compared to the clear corneal incision, which caused greater WTR astigmatism. This study also proved that corneal stability was achieved one week after scleral frown incisions as compared to clear corneal incisions in which case, stabilization of refraction delayed to 1 – 3 months post-operatively.22 On the other hand 47.2 % cases in superior incision group had pre-op against-the-rule astigmatismwhich increased to 81.1 % postoperatively. This finding is similar to results of a study conducted by Hennig and co-authors, in which 85.5 % patients had against-therule astigmatism post operatively at 6 weeks with superior incision.23 In one of related study, authors concluded that with-the-rule astigmatism induced by temporal incision is advantageous because most elderly patients have preop against-the-rule astigmatism.7 Similarly in a study comparing superior and temporal scleral incisions it was showed that a superior incision induced slight against-the rule astigmatism and a temporal incision was associated with slight with-the-rule astigmatic changes.24

CONCLUSION

Both superior and temporal incisions in MSICS resulted in almost same amount of mean astigmatism at 6 weeks (final follow-up) and mean SIA was found to be insignificantly different in both groups. Temporal incision group had the advantage of achieving withthe- rule astigmatism. It was seen in this study that applying superior incision on patients with pre-existing with-the-rule corneal astigmatism could lead to axis shift to against-the-rule astigmatism. So selection of site of incision should be guided by amount and type of preoperative astigmatism.

 


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