Dr. Om Prakash, O05038,
Dr. Sangeeta
Om Prakash (O0538)1, Dr. Sangeeta2
Lady Hardinge Medical College (LHMC) & Associated Hospitals 1, University of Delhi, New Delhi, India (Study conducted at LHMC,)
Introduction:
Patients undergoing cataract surgery may have varying amount of corneal astigmatism. . Modern cataract surgery aims to obtain an astigmatism free eye postoperatively regardless of preoperative astigmatism .Astigmatism management during cataract surgery has two goals , correction or reduction of pre-existing astigmatism and prevention of surgically induced astigmatism. Corneal astigmatism can be affected by several factors like location , size and type of incision etc. during cataract surgery. Clear corneal incision flattens the incised meridian . Thus pre-existing corneal astigmatism can be modified by locating the incision on the steep meridian. Studies have demonstrated that a temporally located corneal incision induces the least postoperative astigmatism. 1, 2 This study evaluated change in preoperative astigmatism and surgically induced astigmatism ( SIA) with3.2 mm clear corneal incision , located on preoperative steep meridian, in patient having pre-existing ≤ 1.0 D corneal astigmatism, after phacoemulsification cataract surgery.
Materials and Methods
This prospective, interventional study, included 30 eyes of 30 consecutive patients with pre-operative corneal astigmatism ≤1.0 D ,scheduled for cataract surgery by phacoemulsification with PCIOL implantation, using clear corneal incision along steep meridian over a period of 1 year, at Lady Hardinge Medical College and Associated Kalawati Saran Children’s Hospital, University of Delhi, New Delhi, India .
The patients having a history of previous ocular surgery or corneal diseases that would affect the corneal refraction, were excluded. A Written informed consent was obtained from each patient.All eyes underwent a complete ophthalmological examination pre‑operatively and at week 1 ,2,4,6 and 8 post‑operatively including a manifest refraction using a refractometer and snellen chart. Astigmatism was measured from the keratometry readings. Data ongender, age, UCVA, manifest refraction, and automatic keratometry (ARK‑510A, NIDEK) were collected.All the operations were performed by a single Surgeon (1) , under peri-bulberanesthesia,using same surgical technique.
A pre-op toric marker was used to mark the 3,6 and 9 o’clock meridian of cornea using marker pen, in siting position, under topical aesthesia. Using the preoperatively placed reference marks, the steep axis was marked using Gimbel mendez fixation ring. A 1mm side port incision, at 90 degree to steep meridian and a 3.2mm, single-plane one –step” stab” , clear corneal incision was made along pre-marked steep meridian with Sapphirekeratome. After Phacoemusification and cortex removal,a three piece hydrophobicfoldable acrylic PCIOL (Sensar, AR40e,AMO, PCIOL) was implanted in the bag .a stromal hydration of the side port and the main incision was done to achieve water tight wound.
Patients were grouped according to incision location (Superior, supero-temporal, temporal). Astigmatism was assessed by using keratometry readings and Surgically induced astigmatism (SIA) was calculated using SIA CALCULATOR version 2.1, based on HOLLADAY’S METHOD of assessing astigmatism with SIA soft excel sheet calculator.All data was organized as central tendencies of: mean, median and SD… Chi square test was used as a test of significance for qualitative variables. A P value of less than 0.05 was considered statistically significant
Results
The mean age of 30 patients was 56.28± 19.6years(range 35 to 86 years). There were 16 men and 14 women. There were 4 patients in Group A (SG) and all were females (n=4). Group B (STG) had 8 male patients (26.7%) 7 female patients (23.3%). Group C (TG) had 8 male patients (26.7%) and 3 female patients (10.0%).Number of cases operated for R/E (right eye) were 16(53.3 %) and L/E (left eye) were 14(46.7 %)
There were 14 patients having corneal astigmatism between 0.10D to 0.50D. Maximum no of patients were in STG (n=10). I6 patients had preoperative astigmatism between 0.5 D to 1 D. out of these 3 belonged to SG, 5 to STG and 8 belonged to TG .There were 15 patient in STG (50%,15/30) , consisting of 10 patients( 33.33%) patient having astigmatism< 0.5 D and 5 patients having astigmatism from o.5 to 1.0 D ( Table 1) .
Table 1: Surgical group’s characteristics
| Surgical groups characteristics | Items | Superior (n, %) | Supero-temporal (n, %) | Temporal (n,%) | Total (n, %) |
| Gender | Male | 0 (0.0%) | 8 (26.7%) | 8(26.7%) | 16 (53.3%) |
| Female | 4 (13.3%) | 7 (23.3%) | 3 (10.0%) | 14 (46.7%) | |
| Total | 4 (13.3%) | 15 (50.0%) | 11 (36.7%) | 30 (100.0%) | |
| Laterality | R/E | 2(6.7%) | 7 (23.3%) | 7(23.3%) | 16(53.3%) |
| L/E | 2 (6.7%) | 8(26.7%) | 4(13.3%) | 14(46.7%) | |
| Amount of astigmatism (D) | 0.10 TO 0.25 | 1 | 5 | 2 | 8 |
| 0.26 to 0.50 | O | 5 | 1 | 6 | |
| 0.51 TO 1 | 3 | 5 | 8 | 16 | |
| Total | 4 | 15 | 11 | 30 |
The pre-operative astigmatism was similar in three groups (0.58±0.26 D in Superior group, 0.47±0.28D in Supero-temporal group,and 0.68±0.28D in Temporal group, P=0.204). We found mean correction of 0.2 D in STG consisting of 10 patients having astigmatism between < 0.5 D and 5 patients having astigmatism between 0.5 D to 1 D. (Table 2)
Table 2: Mean preoperative and postoperative corneal astigmatism
| Astigmatism | Total astigmatism (mean±SD) (n=30) | P-value | ||
| Amount of Astigmatism | Superior (n=4) | Supero-temporal (n=15) | Temporal (n=11) | |
| Pre-operative | 0.58±0.26 | 0.47±0.28 | 0.68±0.28 | 0.204 |
| Post-operative ( 8thweek) | 0.44±0.38 | 0.27±0.13 | 0.35±0.15 | 0.281 |
| correction | 0.14 | 0.20 | 0.33 | |
We found change in amount of astigmatism (Degree) by 21 degree in SG, 18 degree in STG and 13 degree in TG. However this amount of axis shift remained within the limits of predefined degrees of group in our study. In each case this shift was towards WTR astigmatism.(Table3)
Table 3: Change in Amount of Astigmatism (Degrees) between different Groups.
| Astigmatism | Superior (Mean±SD) | Supero-temporal (Mean±SD) | Temporal ((Mean±SD) | P-value |
| Pre-op | 93.50±13.10 | 79.33±38.22 | 113.63±83.87 | .346 |
| Post- op ( 8th week) | 114 ±1.07 | 61..93±2.06 | 100.36± 64.98 | .585 |
| Change in degrees | 20.5 | 17 | 10 |
SIA in superior group, superotemporal group, and temporal group at the end of 8th week was found to be 0.74+/-0.22 @ 124º,0.42+/-0.33 @ 70.13º and0.62+/-0.43 @ 94.90º respectively. Therefore SIA was maximum in superior group, Followed by temporal group and least in Supero-temporal group while making 3.2 mm clear corneal incision along steeper meridian.(Table 4 &5)
Table 4Surgically induced astigmatism (SIA) (Diopter) between different Groups.
| Astigmatism | Superior (Mean± SD) | Supero-temporal (Mean±SD) | Temporal (Mean±SD) | P-value |
| Post-op ( 1st week ) | 0.57±0.33 | 0.41±0.30 | 0.58±0.51 | .521 |
| Week (8th week) | 0.74±0.22 | 0.42±0.33 | 0.62±0.43 | .174 |
Table 5 surgically induced Astigmatism (SIA) (Degree) between Different Groups
| Astigmatism | Superior (Mean± SD) | Supero-temporal (Mean±SD) | Temporal (Mean±SD) | P-value |
| Post-op ( 1st week ) | 108.75± 74.15 | 85.40± 58.75 | 104.81± 24.68 | 0.55 |
| Post- op (8th week) | 124.0± 78.00 | 70.13±54.71 | 94.90± 10.42 | 0.12 |
Discussion:
Early visual rehabilitation and achieving emmetropia remain the main objectives of modern cataract surgery with IOL implantation. It has become important to correct pre-existing corneal astigmatism at the time of cataract surgery. The surgical incision used for cataract surgery flattens the meridian along the surgical incision and leads to steepening of meridian at 90 degrees opposite to main incision. Thus surgically induce astigmatism (SIA ) following cataract surgery is surgeon specific and depends upon several factors like the size, architecture and location of cataract incision.3-8.
We found mean correction of 0.2 D in STG consisting of 10 patients having astigmatism between < 0.5 D and 5 patients having astigmatism between 0.5 D to 1 D. 50% of patients belonged to STG (15/30). Maximum change in astigmatism (Diopter) was found in Temporal group (0.33 D) whereas minimum change was found in superior group (0.14 D).
Our results are similar to the study conducted by Yukihiro Matsumoto et al they studied effect of 3.2mm clear corneal incision in patients with <0.5 D and > 0.5 D astigmatism. In his study Group 2, 18 eyes having preoperative astigmatism of < 0.5 D, received incision at steepest meridian (BENT in 11, 12o’ clock in 4, temporal in 2 and other in 1). In eyes with preoperative astigmatism of 0.5 D or greater, incision was at steepest meridian in 29 eyes (BENT) in 6, 12o’ clock in 16, temporal in 5 and other in 2). They concluded that postoperative astigmatism developed less frequently in patients with BENT incision than in those with 12 o’ clock incision in patients with preoperative astigmatism< 0.5 D .6
Corneal incision flattens the incised meridian and result in simultaneous against the wound change because of steepening of corneal meridian 90 degree away from the incision . However this change also depends up on size of incision. We used 3.2 mm incision along the steeper meridian. The change in amount of astigmatism in term of degree was found to be insignificant.Similar changes have been reported by Chang Rae Rho, MD et al7and Stephan Kohnen, MD et al 8.
Rapid visual rehabilitation following cataract surgery can be achieved by reducing surgically induced astigmatism (SIA) and correcting residual astigmatism.
Supero corneal incisions (12 0’ clock) have been reported to induce greater corneal changes than temporal incision 1, 2. We found surgically induced astigmatism of 0.74 D @ 124 degree in SG, 0.42 D @ 70 degree in STG and 0.62 D @ 94 degree in TG. Chang Rae Rho et al7 studied effects of steep meridian incision of 3.00 mm on corneal astigmatism in phacoemulsification cataract surgery in 95 patients. The study included 33 eyes in SG, 32 eyes in STG and 30 eyes in TG. They found SIA 0.46 @ 92, 0.40@85 and0.28@ 79 degree in respective groups. We found similar results in SG and STG. The change was greatest when the clear corneal incision was made on superior side of cornea along the steeper meridian as compared to when it was made on temporal or superotemporal side along the steep meridian. Kohnenet al8 reported 0.75 D SIA with temporal clear corneal incision as compared to 1.55 D SIA with nasal clear corneal incision.Post-operative astigmatism has been reported to develop less frequently in patients with BENT incision. (9 and 12 0’ clock) 45 as compared with those 12 o’ clock incision.
However SIA may vary in different studies because of difference in size of incision, number of patients and range of pre-operative astigmatism in inclusion criteria.
References
- Tejedor J, MurubeJ . Choosing the location of corneal incision based on pre- existing astigmatism in phacoemulsification. Am J Ophthalmology 2005:139:767-776.
- Kohnen T, Mann PM, Husain SE, Abarca A, Koch DD. Corneal topographic changes and induced astigmatism resulting from superior and temporal scleral pocket incisions. Ophthalmic Surg Lasers 1996; 27:263-269.
- Basati S, Vasavada AR, Thomas R, Padhmanabhan P. Extracapsular cataract extraction: surgical techniques. Indian J Ophthalmol 1993; 41: 195-210.
- Kawano K. Modified corneoscleral incision to reduce postoperative astigmatism after 6mm diameter intraocular lens implantation. J Cataract Refract Surg 1993; 19: 387-398.
- Ken Hayashi, MD, Motoaki Yoshida, MD, Koichi Yoshimura, MD. Effect of steepest –meridian clear corneal incision for reducing preexisting corneal astigmatism using a meridian –marking method or surgeon’s intuition. J Cataract Refract Surg 2014; 40: 2050-56.
- Yukihiro Matsumoto, MD, Tsutomu Hara, MD, Keizo Chiba, MD Makoto Chikuda, MD. Optimal incision sites to obtain an astigmatism-free cornea after cataract surgery with a 3.2 mm sutureless incision. J Cataract Refract Surg 2001; 27: 1615-1619.
- Chang Rae Rho, MD, Choun-Ki Joo, MD, PhD. Effects of steep meridian incision on corneal astigmatism in phacoemulsification cataract surgery. J Cataract Refract Surg 2012; 38: 666-671.
- Stephan Kohnen, MD, Ralph Neuber, MD, Thomas Kohnen, MD. Effect of temporal and nasal unsuturedlimbal tunnel incisions on induced astigmatism after phacoemulsification. J Cataract Refract Surg 2002; 28: 821-825.