14, 15 Because of the special conditions, leading to changes of the inferior corneal surface, in most cases only rigid gas permeable contact lenses with a special back surface design can lead to optimal fit and visual results. 12, 13 Among the different kinds of contact lenses a rigid gas permeable lens may be the correction of choice, since this type of lens provides good visual acuity, corrects high degrees of regular and irregular astigmatism, has high oxygen permeability, and, in comparison with soft contact lenses, carries a lower risk of microbial keratitis (incidence 1/10 000) and corneal neovascularisation. In these cases contact lens fitting is a good option.
![keratoconus pellucid marginal degeneration keratoconus pellucid marginal degeneration](https://c1.staticflickr.com/9/8089/8503544485_0e86e66b37_b.jpg)
Patients with high or irregular astigmatism cannot be corrected with spectacles. The non‐surgical approaches to the management of the high and irregular astigmatism in patients with PMCD include spectacles and different groups of contact lenses. Thus, surgical intervention should be delayed as long as possible. 7, 8, 9, 10 None of the present methods of treatment reliably achieve an optimum visual result. Surgical options to improve the irregular corneal conditions include intrastromal corneal rings, thermocauterisation, and a great variety of different types of keratoplasty. 3, 4 Reported complications are hydrops 5 and spontaneous perforation. Videokeratoscopic colour coded maps show a marked flattening of the cornea along a vertical axis and a steepening of the inferior cornea peripherally to the site of the lesion resulting in a clinically irregular and against the rule astigmatism. Patients present in their third to fifth decade of life with a decrease of visual acuity because of high and irregular astigmatism. Eyes may be affected asymmetrically and rarely the degenerative area may be located superiorly. The area between limbus and the thinning is clear, without any scarring, lipid deposition or vascularisation. The epithelium of the thinned out area is intact with an ectatic cornea superior to the thinning. A 1–2 mm margin of normal cornea lies between the thinning and the limbus. This new topographic analysis might be useful in the diagnosis and tracking of corneal ectatic diseases.Pellucid marginal corneal degeneration (PMCD) is a bilateral progressive ectatic corneal disorder characterised by a non‐inflammatory inferior peripheral band of thinning extending from the 4 o'clock position to the 8 o'clock position. Gaussian fitting of mean curvature maps accurately quantifies the peak location and amplitude of the cone in keratoconus and PMD eyes. Advanced keratoconus tended to have higher cones (amplitude 13.31 +/- 6.87 diopters) than early keratoconus (amplitude 10.65 +/- 1.56 diopters). The locations of peaks on axial and tangential maps differed considerably from those on mean curvature maps. According to Gaussian fitting, the vertical cone peak locations were -1.10 +/- 0.43 mm (mean +/- SD) in keratoconus eyes and -1.94 +/- 0.53 mm in PMD eyes (P <. The Gaussian function provided an excellent model of keratoconus on mean curvature maps, with a mean cross-correlation of 0.80. However, the peak location and appearance of the same conic distortion on axial and tangential maps were greatly influenced by coexisting astigmatism.
![keratoconus pellucid marginal degeneration keratoconus pellucid marginal degeneration](https://core4.bmctoday.net/storage/images/0320_CLBT_SBFig_1583524565.png)
Computer simulations showed that the peak on the mean curvature map accurately represented the peak of the cone-like distortion. Keratoconus and PMD eyes had a characteristic localized increase in convexity (cone) on mean curvature maps. Computer simulations of keratoconic corneal topography were used to help interpret the results. The peak location and amplitude of distortions were quantified by fitting two-dimensional Gaussian functions. Keratometric mean curvature maps were computed from a placido-disk-based corneal topography system. To characterize keratoconus and pellucid marginal degeneration (PMD) on mean curvature maps.Ī retrospective analysis of clinical records of 19 keratoconus eyes and eight PMD eyes.