Astin, Christine Lesley Katherine; (1995) Corneal parameter changes after cataract extraction. Masters thesis (M.Phil), UCL (University College London).

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Abstract

National health services are receiving increased pressure to improve cost efficiency and quality of patient treatment outcome. Hence it is useful to re-evaluate corneal changes following cataract extraction, with a view to minimising astigmatism and corneal contour stabilisation time, such that patients can more rapidly obtain their best corrected vision and return to independent life. In a prospective study of 140 patients undergoing routine extracapsular cataract extraction, the changes in retraction, in corneal curvature as determined by keratometry and keratoscopy, and in regional corneal thickness were closely monitored preoperatively and for 6 months postoperatively. Two groups were compared, one (C) receiving a corneal incision and nylon sutures, the other (L) receiving a limbal incision and silk sutures. Both groups demonstrated a large 'with the rule' (steep meridian vertically) astigmatic shift immediately postoperatively. The group showed faster stabilisation of retractive (8 to 10 weeks) and corneal astigmatism (8 weeks;, and a moderate final mean 'against the rule' astigmatism value. The (C) group remained as 'with the rule' and stabilised later for refractive (12 weeks; and corneal astigmatism (16 weeks). Keratoscopy indicated similar central curvature changes but the pattern for the peripheral corneal shape changes had a large variability, which was also shown by the two control groups. Although greater corneal thickness change had been anticipated tor the (C) group than the (L) group, no significant difference was found between the two groups even by their stabilisation time or about 10 weeks postoperatively. Only when comparing overall changes was (C) group found to show the greater amount. Using the results, a flow chart guide was created for consideration by surgeons to help produce the most desirable optical outcome. A predictive second study of 45 patients demonstrated the valuable advantage of using this chart in conjunction with preoperative measurements, causing the majority of the patients to obtain minimal or appropriately balanced ocular astigmatism by 6 to 8 weeks and therefore a more satisfactory optical result.

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