We randomly selected and analyzed one eye from 130 normal subjects and one eye from 74 consecutive keratoconic subjects from a population of patients seeking refractive surgery at the London Vision Clinic. All subjects were scanned with the Artemis-1 (ArcScan, Inc., Morrison, CO) very high-frequency (VHF) digital ultrasound system.
Preoperative assessment of all patients included manifest refraction, logMAR corrected distance visual acuity (CDVA) (CSV-1000; Vector Vision, Inc., Greenville, OH), and cycloplegic refraction using one drop of tropicamide 1% (Alcon Laboratories UK Ltd., Hemel Hempstead, UK. Tomography was assessed using the Orbscan II (Bausch & Lomb, Claremont, CA), and topography and simulated keratometry (K) were assessed using the Atlas corneal topography system (Carl Zeiss Meditec AG, Dublin, CA). Dynamic pupillometry was carried out using the Procyon P2000 pupillometer (Haag-Streit, Bern, Switzerland). Wavefront assessment was performed using the WASCA aberrometer (Carl Zeiss Meditec AG). Single-point pachymetry was performed with the Corneo-Gage Plus (50 MHz) handheld ultrasound pachymeter (Sonogage, Cleveland, OH) by determining the minimum of 10 consecutive central total corneal measurements. Three-dimensional epithelial, stromal, and total corneal thickness for the central 8- to 10-mm diameter was measured using the Artemis-1 technology.
Keratoconus diagnostic criteria included (a) patients previously diagnosed with keratoconus and (b) patients whose diagnosis was confirmed by clinical signs of keratoconus such as microscopic signs at the slit lamp, corneal topographic changes, high refractive astigmatism, reduced CDVA and contrast sensitivity, and significant level of higher-order aberrations, in particular coma. The population included eyes at different stages of the disease, ranging from cases with indisputable keratoconus by topography, but without microscopic signs at the slit lamp, to extreme cases approaching the need for corneal transplant, demonstrating clear microscopic signs such as Vogt striae and substantial corneal thinning. In patients in whom the second eye demonstrated suspected keratoconus (i.e., a diagnosis of keratoconus could not be confirmed), the second eye was excluded. Patients with pellucid marginal degeneration and eyes with pathology other than ectatic degeneration (e.g., corneal scarring) or hydrops were also excluded.
Contact lens wearers (65% of normal and 45% of keratoconus eyes) were not excluded; however, the majority of these had not worn their contact lenses over a suitable washout period (i.e., 1 week for soft contact lenses and 1 month per decade of wear for rigid contact lenses). In total, only 8% of normal eyes and 27% of keratoconus eyes had worn contact lenses within the washout period.
Keratoconus eyes were graded by the Krumeich criteria,
38 which depend on mean anterior curvature K-readings, minimum corneal thickness, and refractive error.
The research followed the tenets of the Declaration of Helsinki. Informed consent for research, analysis, and publication of data was obtained from patients. The research was conducted under protocols approved by Western Institutional Review Board and the Institutional Review Board of the Columbia University Medical Center.