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Abstract
Pterygium is a common disorder seen in hot climate countries as apart of pterygium belt that was described by Cameron. It is a fibrovascular connective tissue proliferation extending on the cornea in the interpalpebral space. Symptoms of this disorder includes foreign body sensation, lacrimation, redness of the eyes, decrease in visual acuity (due to invasion on the visual axis, induced astigmatism or tear film abnormality), diplopia and cosmetic disturbances. The progression of pterygium on the cornea can lead to both significant corneal distortion and development of large amount of corneal astigmatism. pterygium induced astigmatism can be the cause of subjective visual complaint, including decrease of visual acuity, glare sensitivity and monocular diplopia. It has been postulated that the cause of astigmatism is tear film pooling at apex of pterygium, the proposed mechanism is tear meniscus developing between corneal apex and developing pterygium, causing an apparent flattening of the normal corneal curvature in that area.
Another possible explanation is traction on the cornea by the pterygium(due to in growth of the fibrovascular tissue); this is sometimes obvious and may restrict ocular motility. Richard G Lindsay et al found that there is significant correlation between the extension of pterygium on the cornea and amount of induced astigmatism. pterygia appear to have minimal effect on cornea till it reach 45% of corneal radius (or reach within 3mm of visual axis) once this critical size is reached, increasing degrees of astigmatism are induced. pterygium excision usually improves visual acuity, reverses pterygium related corneal flattening, consequently, successful pterygium surgery should reduce pterygium induced refractive astigmatism and improves visual outcome.
This may add one indication for excision of pterygia other than encroachment on visual axis or cosmetic reasons or limitation of abduction of eye.
This study evaluates the refractive and keratometric changes that occurs after pterygium excision, as pterygium is known to affect refractive astigmatism, which can have a significant impact on vision.
This study was done on thirty eyes of twenty nine patients with primary pterygia .All cases were submitted to preoperative evaluation in the form of : history taking, visual acuity testing(uncorrected and best corrected visual acuity), slit lamp examination (for grading of pterygium extension on the cornea.), refraction(measuring both spherical error and cylindrical error of refraction), keratometric examination(measuring both vertical keratometric reading and horizontal keratometric reading.), then all cases were submitted to pterygium excision with bare scleral technique. The cases were followed up for three months postoperatively repeating the preoperative examination at one month and three months. The result of this follow up was improvement in uncorrected visual acuity, best corrected visual acuity, decrease of preoperative astigmatism and spherical error, steepening of horizontal corneal meridian