An evaluation of the keratoconic cornea using computerised corneal mapping and ultrasonic measurements of corneal thickness

Abstract

Reports indicate the presence of up to three independent cone shapes in keratoconus (round/oval/global) but the preponderance of one cone over another is unclear. This work evaluates keratoconic corneal topography and corneal thickness using videokeratoscopy and ultrasound pachometry, respectively. An EyeSys videokeratoscope (VKS) (EyeSys Laboratories, Houston, TX, USA) was used to assess the topography of 54 keratoconic eyes (27 subjects) and 27 age-matched normals. In addition, ultrasonic pachometry measurements were made over 14 known areas in normal and keratoconic eyes. Corneal thinning was significant for all keratoconic areas measured except for the far temporal cornea. A correlation between corneal radius and thickness was evident. Analysis of cone shape revealed a potential fourth variety: the asymmetric bow-tie cone. Further topographic evaluation of this cone entity using the VKS revealed its dependence on gaze direction which may account for apparent differences in progression patterns between round and bow-tie cones.

The Dundee University Scottish Keratoconus study: demographics, corneal signs, associated diseases, and eye rubbing

“…26 In DUSKS, 88.5% were found to exhibit bilateral keratoconus, usually asymmetrical in presentation (P ¼ 0.005). Fleischer's-ring was the most frequently observed corneal sign (86-89%) as reported previously 2,27 followed by Vogt's striae (67-68%) and corneal scarring (21-20%) at review 1 and 2, respectively. Notably, corneal slit-lamp signs cannot be relied upon solely as diagnostic criteria as approximately 15% of eyes exhibited no corneal signs despite pathognomonic topographic signs of keratoconus.…”

Corneal-thickness spatial profile and corneal-volume distribution: Tomographic indices to detect keratoconus

“…[34][35][36][37][38][39] Mandell and Polse 34 pioneered the investigations of corneal thickness profile in a study using a modified Haag-Streit optical pachymeter with an electronic recording system to document the variation in thickness over the horizontal meridian measured at different angles. In their study, the difference between the central and the peripheral measurements was much greater in eyes with keratoconus; it was most significant at the 35-degree position, where the authors found a difference greater than 0.085 mm as pathognomonic of keratoconus.…”

“…36 Regional measurements and mapping of corneal thickness are also possible using ultrasound computed tomography single-point measurements. 38,39 However, ultrasound computed tomography does not provide data from the true thinnest point and the angulation of the probe might also account for error in the case of regional thickness measurements. In addition, ultrasound computed tomography does not allow precise localization, even for the central point, and proper training is required for reproducible results.…”

Quantitative analysis of corneal microstructure in keratoconus utilising in vivo confocal microscopy

“…[40][41][42][43] In our study an empirical combination of corneal apex power 44 and thickness was used. 45 Therefore, in this context the in vivo confocal microscopy data may not always be readily correlated with the small number of published studies on the topic. Erie et al 35 observed that the decrease in the keratocyte density, in a study of mild to moderate keratoconus was only in association with contact lens wear.…”