COMPARATIVE PROSPECTIVE STUDY OF ASTIGMATISM BEFORE AND AFTER PTERYGIUM EXCISION IN A TERTIARY CARE CENTRE”

Objective: The objective of this study is to evaluate the change in corneal refractive status before and after Pterygium excision. Methodology: 31 patients who underwent Pterygium excision were evaluated pre-operatively and post-operatively for the assessment of astigmatic changes. All the patients having Pterygium more than grade II underwent Pterygium excision with conjunctival autografting. Pre-operative and post- operative assessment of astigmatism was done by objective refraction with Streak Retinoscope. Further, the subjective refraction was calculated and then keratometry was done by using manual Bausch & Lomb Keratometer. Post-operative astigmatism was measured after 1 week, 1month and 3months, to estimate how much astigmatism improvises withtime. Result:All patients who underwent Pterygium excision were analyzed retrospectively, the mean age was 39.04 Â± 9.91 years which ranged from 19-60 years. 70.9% cases were having grade II Pterygium, 25.8% patients were having grade III Pterygium and only one case had grade IV Pterygium. The mean preop astigmatism in grade II Pterygium was 1.10 Â± 0.7, in grade III Pterygium it was 1.5 Â± 1 and in grade IV it was 6. The post op mean astigmatism in grade II Pterygium was 0.21, in grade III it was 0.4 and in grade IV it was 1. There was good correlation between grade of Pterygium and astigmatism with r-0.528. In all the grades of Pterygium the differences between the preoperative astigmatism and postoperative astigmatismwas clinically significant with p value 0.001. Conclusion: In cases of Pterygium, early intervention in the form of Pterygium excision with conjunctival autograft effectively reduces the amount of astigmatism, thus reducing the amount of refractive cylinder and so leads to an improvement in visual acuity.

The induced astigmatism may become significant to cause visual distortion, even in early stages of Pterygium which remains distant from the visual axis. As the progression of a Pterygium onto the cornea occur it causes significant corneal distortion and the development of large amounts of corneal astigmatism. Pterygium-induced astigmatism can be the cause of subjective visual complaints, including decreased visual acuity, glare sensitivity and monocular diplopia. 7 Astigmatism is a type of refractive error where the refraction varies in different meridian. Consequently, the rays of light entering the eye cannot converge to a point focus but form focal lines.8 Refractive error is one of the causes of reversible blindness in India. According to World Health Organization (WHO) the prevalence of blindness due to refractive error in India is1.34%.9 Studies suggest that the prevalence of astigmatism related refractive error can be reduced through Pterygium excision. 10 Hence in this study, an effort is made to compare Theextent of astigmatic changes after pterygium excision.
Aims And Objectives:- 1. The objective of this study is to evaluate the change in corneal refractive status before and after Pterygiumexcision. 2. To assess the improvement in visual acuity following Pterygiumexcision.

Keratometer
The radius of curvature of the central cornea can be measured using a keratometer. Two main types are available but both measure the radius of curvature of a central zone of the cornea approximately 3mm in diameter. The central or axial area of the cornea, about 4mm in diameter, is usually assumed to be a spherical refracting surface. The keratometer thus read within this zone. The radius curvature of the axial zone of the emmetropic eye is about 7.8mm.The optical power of the cornea can also be expressed in dioptres. The precise value is determined by curvature of the anterior and posterior surfaces as well as the refractive indices of the cornea and the media at each surface, however for most cornea an approximation is provided by the keratometer equation in which the refractive index of tear is standardized to 1.3375 so that a radius of curvature of 7.5mm corresponds to45D. The more peripheral cornea is flatter and non-spherical. Optically, it is the central 4mm spherical zone which is utilized for vision, the periphery being screened off by the pupil. Visual acuity suffers when the pupil is widely dilated.

Material And Method:-
It is a case series study of 31 patients having Pterygium who fulfill the inclusion criteria and are willing to undergo Pterygium surgery. This study was conducted in the department of ophthalmology, Santhiram medical college and general hospital, Nandyal. All the cases were evaluated and managed at ourhospital.
Written informed consent (in English and local language) was taken from all study subjects, before enrolment in the study. A detailed protocol was made after referring several books and literature and after consulting concerned surgeons of the department.
All the patients were admitted as per protocol and Written Informed consent to be taken one day prior to surgery. These patients were underwent complete eye examination, including full history of any previous ocular disease or surgery and routine investigation and evaluation. All the patients having Pterygium more than grade II underwent Pterygium excision with conjunctival autografting. Pre-operative and post-Operative assessment of astigmatism was done by objective refraction with Streak Retinoscope. Further, the subjective refraction calculated and then Keratometry was done by using manual Bausch & Lomb Keratometer

Selection Criteria
Inclusion criteria for the study group: Patient with primary Pterygium grade II in one or both eyes will be included in the study.
Exclusion criteria for the study group: 1. Patient with recurrent Pterygium, pseudopterygium, keratoconus, lenticonus, corneal dystrophy were excluded from thisstudy. 2. Patient with cataract and retinal disease where Pterygium excision will not help in visual acuity improvement, were excluded from thisstudy.

Pre Operative Assessment
Patients were admitted one day before surgery. Detailed history was taken of each patients and anterior segment examination was performed using slit lamp examination. All patients Pterygium grading was done. Pterygium was graded depending on the extent of the corneal involvement: Grade I crossing limbus, Grade II -midway between limbus and pupil, Grade III -reaching up to pupillary margin, Grade IV -crossing pupillary margin. Visual acuity was checked with snellen's visual acuity chart. Ocular movements assessed in all nine gazes for presence of any restriction of movement. Keratometry reading using Bausch and Lomb keratometer was done for all cases. After pupillary dilation detailed fundus examination done using indirect ophthalmoscopy or 90D lens and Retinoscopy wasdone.

Preoperative Treatment:
All the patients were given preoperatively topical eye drop flubichlor four times a day which contain flurbiprofen and chloramphenicol.

Preoperative Preparation:
For all the case eyelashes were trimmed, xylocaine sensitivity test was done.
Lacrimal sac patency was checked before surgery

Observation And Results:-
It is a case series study, comparing the occurrence Astigmatism before and after Pterygium excision at Santhiram medical college, Nandyal .Total 31 cases were studied after obtaining approval from the institutional ethical committee and written informed consents for both the study and pterygium excision procedure were taken from the patients in their own language . Most of cases were female genders who were farmer by occupation. In this study 31 cases, underwent Pterygium excision which were analyzed retrospectively. The mean age was found to be 39.04 ± 9.91 years which ranged from 19-60 years. Majority of patients were in the range of 30-40years that is 32.2%, 29% were between 40-50year age, 22.5% patient were in between 20-30years age, 12.9% were between 50-60 years and only 3.2% patients were between 10-20 years. [ Table 2,Graph2] In this present study out of 31 cases preoperatively, 6.4% cases had vision between PL+ve -CF at 3Mtrs, 35.4% cases had vision between CF at 3Mtrs to 6/60, 22.5% cases had vision between 6/60 to 6/24 and 35.4% patients had vision between 6/24 to 6/6. Postoperatively majority of patients (90.4%) had visual acuity between 6/24-6/9 and 9.6% patients had vision between 6/60 to 6/24. There was a statistical significance between preoperative and postoperative visual acuity with p value 0.0001. [ Table 3, Graph 3]       The mean pre-op astigmatism in grade II Pterygium was 1.10 ± 0.7D, in grade III Pterygium it was 1.5 ± 1D and in grade IV it was 6D. It was evident that pre-op astigmatism increases with the increase in Pterygium grading. The post-op mean astigmatism in grade II Pterygium was 0.21±0.2D, in grade III it was 0.4±0.2D and in grade IV it was 1D. There was a good correlation between grades of Pterygium and astigmatism with correlation coefficient r-0.528. In all the grades of Pterygium the differences between the preoperative astigmatism and post operative astigmatism was clinically significant with p value 0.001.

Discussion:-
In this study, 22 patients were female and 9 were male but in other similar studies, male patients have a higher preponderance, except Errais K et al 2004. One would expect a higher incidence in males as they are more exposed to UV radiation. The likely reason behind the above differences was, while choosing patients randomly we got more number of female patients who were outdoor laborworker 6/24 to 6/6.Postoperatively of patients had visual acuity between 90.4% between 6/24-6/9 and 9.6% patients had vision between 6/60 to 6/24.There is a statistical significance between preoperative and postoperative visual acuity with p value 0.0001.So it suggested that Pterygium causes a significant vision loss due to induced astigmatism and excision of Pterygium improved the visual acuity inpatients.
Among the 31 patients 54.8% had right eye Pterygium and 45.2% had left eye Pterygium, but the difference is not clinically significant. From this we infer that there is no association between Pterygium and laterality.
The differences between pre operative and post operative astigmatism was clinically significant with p value 0.0001.From the above we infer that the astigmatism differences between pre and post operative day 1 was 0.6D, which at post op 1week, furthered decreased to 0.54D. At end of 1 month, it deceases to 0.12D and at end of 3months it deceases furthermore to 0.08D. So the mean Keratometry astigmatism was consistently decreasing till the end of 3month with peak differences at 1st post operative day followed by post op 1week.
Majority of the cases have with the rule astigmatism changes, which varies from 0.5 to 6D.Among the 31 Pterygium cases, preoperatively 67.8% had with the rule astigmatism, 25.8% had against the rule astigmatism and only 6.4% were not having any astigmatism and postoperatively 45.16% had with the rule astigmatism,19.35% patients had against the rule astigmatism.
After Pterygium excision, there was a 22.6%decrease in with the rule astigmatism and no changes noted in against the rule astigmatism and 29.1% patients increases towards no astigmatism. A pterygium generally causes localized flattening central to the apex of the pterygium.As this flattening is along the horizontal meridian, it usually causes with-the-rule cornealastigmatism.
The Pterygium was graded and astigmatism was calculated pre operatively and postoperatively, The preoperative astigmatism in grade II pterygium1.10 ±0.7D which became 0.21 ± 0.2D postoperatively so there was a change of 0.9 ± 1 D astigmatism observed.In grade III Pterygium the preoperative mean astigmatism was 1.5 ± 1D which at postoperatively became0.4 ± 0.2D. Here also difference of 1.1±1D astigmatism was observed and in grade IV Pterygium preoperative mean astigmatism was 6D and which became 1D postoperatively&hugedifferenceof 5D astigmatism was observed.
This studies shows that, in cases of grade II & III Pterygium if operated showed 1-1.5D change in astigmatism, but in patients with grade IV Pterygium, after surgery there was drastic shift in astigmatism of5D.

Conclusion:-
This comparative study of astigmatism changes before and after pterygium excision among 30 patients having greater than grade II pteygium helped us in certainconclusions.