METHODS—A total of 360 topographic maps obtained with the TMS-1, from 95 eyes that had undergone penetrating keratoplasty (PKP), were reviewed independently by two examiners in a masked fashion, and were categorised according to a proposed classification scheme. RESULTS—A high interobserver agreement (88% in the first categorisation) was achieved. At 12 months post-PKP, a regular astigmatic pattern was observed in 20/85 cases (24%). This was subclassified as oval in three cases (4%), oblate symmetric bow tie in six cases (7%), prolate asymmetric bow tie in six cases (7%), and oblate asymmetric bow tie in five cases (6%). An irregular astigmatic pattern was observed in 61/85 cases (72%), subclassified as prolate irregular in five cases (6%), oblate irregular in four cases (5%), mixed in seven cases (8%), steep/flat in 11 cases (13%), localised steepness in 16 cases (19%), and triple pattern in three cases (4%). Regular astigmatic patterns were associated with significantly higher astigmatism measurements. The surface asymmetry index was significantly lower in the regular astigmatic patterns. CONCLUSIONS—In post-PKP corneas, the prevalence of irregular astigmatism is about double that of regular astigmatism, with a trend for increase of the irregular patterns over time.
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Selected References
These references are in PubMed. This may not be the complete list of references from this article.
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Schematic illustration of the criteria for determination upon regularity and symmetricity of a topographic pattern. Firstly, a line bisecting the two lobes of the bow tie is drawn. If the skewing between the two is greater than 20° the pattern (more ...)
Examples of different topographic patterns. (A) Unclassified pattern, (B) oval (prolate) astigmatic pattern with central area of steepening; (C) prolate symmetric bow tie (PSBT) pattern; (D) prolate asymmetric bow tie (PABT) pattern; (E) oblate symmetric (more ...)