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S. Haque, L. Jones, T. Simpson; CORNEAL AND EPITHELIAL THICKNESS IN KERATOCONUS: A COMPARISON OF ULTRASONIC PACHYMETRY, ORBSCAN AND OPTICAL COHERENCE TOMOGRAPHY MEASUREMENTS. . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2891.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To measure corneal and epithelial thickness in keratoconic subjects, using three techniques – Optical Coherence Tomography (OCT), OrbscanTM (ORB) and ultrasonic pachymetry (UP). Methods: Twenty keratoconic and five control subjects were enrolled. The single appointment commenced with a visual acuity and slit–lamp assessment (with contact lenses removed). The OrbscanTM was initially utilised to locate the steepest area of the cornea, which was taken to represent the cone apex. Each of the three instruments was used to obtain four thickness measurements; from the cone apex, corneal centre, mid–nasal and mid–temporal cornea. Results: In the keratoconic subjects, mean central corneal thickness (CCT) measured by UP, ORB and OCT was 494±53um, 439±56um and 434±47um respectively; (p=0.000). The central keratoconic cornea was 57um thinner than the normal cornea; [F(2,38)=9.58, p=0.000]. As expected, the cone apex was thinner than the central cornea for all instruments; [F(6,34)=13.1, p=0.000]. Epithelium measurements were obtained from OCT readings. The keratoconic epithelium was 43.9±4um in the centre and 42.5±4um at the apex; [F(3,54)=7.61, p=0.000]. Across the horizontal meridian, epithelium in keratoconics was approximately 8um thinner than in normal subjects; (post–hoc p<0.005). Comparing methods, ORB and OCT were most highly correlated, in the measurement of both CCT (r=0.878) and corneal apex (r=0.827). All three techniques produced similar readings for measurements of mid–nasal and mid–temporal cornea; (post–hoc p>0.05). Conclusion: Generally, ultrasonic pachymetry produced the highest corneal thickness readings in the centre and apex, compared to OrbscanTM and OCT, which produced similar thickness values. Corneal and epithelial thickness in the keratoconic patient varied significantly across the cornea and was thinner than in normal subjects.
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