Karthik, Srinivasan (2008) Effect of Pterygium on Corneal Astigmatism. Masters thesis, Aravind Eye Hospital and Postgraduate Institute of Ophthalmology, Madurai.
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Abstract
INTRODUCTION : A pterygium is a triangular fibrovascular overgrowth or extension of connective tissue from the bulbar conjunctiva to the cornea. A pterygium that is confined to 1 to 2 mm of the peripheral cornea has little effect on vision and maybe of only cosmetic concern. As the pterygium advances, however, induced irregular astigmatism can cause decreased visual acuity. The amount of the induced astigmatism, however small is measured using corneal topography. A significant amount of corneal astigmatism can be induced by the encroachment of the pterygia on the cornea. The pterygium usually causes with the rule astigmatism that is hemimeridional on the side of the pterygium. There is significant correlation between the extension of the pterygium onto the cornea and the amount of corneal astigmatism induced. However there is poor correlation between pterygium induced corneal astigmatism measured topographically and that measured by manifest refraction. Using renewed optical beam scanning topography by the use of the hybrid scanning slit and placido disk we can measure the cornea with an imperfect tear film which maybe encountered in the pterygium cases and as the measurements are carried out independently for the anterior and posterior surfaces the actual corneal index (1.376) of refraction can be used for the power calculations instead of the empirically derived keratometric index of refraction (1.3375). OBJECTIVE : To determine the effect of pterygium on corneal astigmatism. DESIGN: Prospective study. METHODS: Fifty patients with pterygium will be selected and the extension of the pterygium will be measured using the slit lamp and the corneal astigmatism will be measured using corneal topography (Orbscan). Correlation of the data will be discussed. MAIN OUTCOME MEASURES : Corneal astigmatism, pterygium size. MATERIALS AND METHODS : PATIENTS AND METHODS: Inclusion Criteria: 1. Age more than 18 years. 2. Any type of pterygium with the pterygium classified into either Primary, atrophic or recurrent pterygia. 3. Growing pterygium, which invaded more than 1mm into the cornea. Exclusion criteria: 1. Recurrent pterygium, 2. Eyes with any corneal pathology, 3. Double pterygium. This study included a series of 50 patients selected within the constraints of the inclusion criteria. The patients’ history of presenting illness is noted and history of hours spent outdoors and history of the use of sun protection were enquired. Then the patient was examined under diffuse illumination and by using the slit lamp. The size of the pterygium its extent were noted and the pterygium was graded accordingly by using the horizontal beam of the slit lamp. The orbital anatomy was noted and also the normalcy of the lid closure was noted. After this is done the patient then underwent refraction by a refractionist, manual keratometry readings were obtained. Then the patient was screened using a Orbscan machine. Results were depicted as scatter plots and bar graphs and analysed by linear regression to determine the relationship between diopters of induced astigmatism and the size of extension of the pterygium. CONCLUSION : Pterygia are fibrovascular growths extending from the bulbar conjunctiva onto the cornea. Once the pterygia reach a critical size they induce visually significant central with the rule astigmatic changes that may not be apparent by subjective refraction. 1. Of the 50 patients in the study group 52% were males and 48% were females. 2. 54% of the patients were in the age group of 40-50 years, 34% in the age group of 51-60 years and 12% were in the age group of 61-70 years. 3. Majority of the patients 98% had a nasal pterygium and were of the Grade T2. 4. There was a significant correlation found between the size of the pterygium and the induced astigmatism (r-value 0.940 and p value of 0.00) as by Pearson correlation. The amount of astigmatism measured in our patients represents the naturally occurring astigmatism plus the induced effect of the pterygium. Correlation between these two can only be estimated when the pterygium has been removed surgically and the corneal topography done post operatively. To conclude of the 50 patients in our study all the patients had induced with the rule astigmatism and the amount of astigmatism increases with the increase in the size of the pterygium. There was a significant correlation found between the size of the pterygium and the induced astigmatism (r-value 0.940 and p value of 0.00) as by Pearson correlation. In this study there was a positive correlation between the size of the pterygium and the amount of induced astigmatism measured by using corneal topography. Based on the results of this study we believe that the corneal topography analysis is an additional tool in the evaluation of the patient with pterygium allowing the measurement of optical changes in the cornea.
| Item Type: | Thesis (Masters) |
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| Uncontrolled Keywords: | Pterygium ; corneal astigmatism. |
| Subjects: | MEDICAL > Ophthalmology |
| Depositing User: | Devi S |
| Date Deposited: | 28 Feb 2018 11:05 |
| Last Modified: | 01 Mar 2018 05:15 |
| URI: | http://repository-tnmgrmu.ac.in/id/eprint/5909 |
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