Central corneal thickness measurements: using an ultrasonic instrument and 4 optical instruments.

Purpose: Both between-session and within-session repeatability were determined for measurement of corneal thickness with the following techniques: ultrasound pachymetry (UP), confocal microscopy (CS), Orbscan pachymetry (ORB), spectral oscillation interferometry (SOI), and optical coherence tomography (OCT).

Methods: The right eyes of 20 normal subjects were tested on 2 different days. For each session, 2 central corneal thickness measurements were determined using the ConfoScan 3 microscope, the Orbscan system, and the Stratus OCT system; 5 measurements were found with the Sonogage ultrasound pachymeter; and between 2 and 10 measurements were found with the SOI system.

The influence of gender and hormone status on the severity and progression of keratoconus.

Purpose: To assess the effects of gender and hormone status on the severity and progression of keratoconus in patients enrolled in the Collaborative Longitudinal Evaluation of Keratoconus Study.

Methods: The severity and progression of keratoconus in both men (M) and women were evaluated over a 4-year period that encompassed menopausal transition for hormone-active women (HA) and hormone-inactive women (HI). Four outcome measures were selected as indicators of the severity of keratoconus: high-contrast best-corrected visual acuity, low-contrast best-corrected visual acuity, the steep keratometric measurement, and corneal scarring (yes/no).

Sex- and gender-based differences in healthy and diseased eyes.

Purpose: The aim of this study was to identify sex- and gender-based differences in ocular anatomy, physiology, and disease susceptibility or manifestation.

Methods: Review of current indexed literature was conducted.

Results: Sex and sex hormones influence the lacrimal system, eyelids and blinking, corneal anatomy and disease, aqueous humor dynamics and glaucoma, crystalline lens and cataract, uveitis and retinal disease, ocular circulation, and optic nerve anatomy and disease.

The contribution of lipid layer movement to tear film thinning and breakup.

Purpose: To investigate whether the tear film thinning between blinks is caused by evaporation or by tangential flow of the tear film along the surface of the cornea. Tangential flow was studied by measuring the movement of the lipid layer.

Methods: Four video recordings of the lipid layer of the tear film were made from 16 normal subjects, with the subjects keeping their eyes open for up to 30 seconds after a blink.

Contributions of evaporation and other mechanisms to tear film thinning and break-up.

Purpose: To evaluate the contribution of three mechanisms-evaporation of the tear film, inward flow of water into the corneal epithelium or contact lens, and "tangential flow" along the surface of epithelium or contact lens-to the thinning of the tear film between blinks and to tear film break-up. In addition to a discussion of relevant studies, some previously unpublished images are presented illustrating aspects of tear film break-up. CONTRIBUTIONS OF THREE MECHANISMS TO TEAR FILM BREAK-UP: Inward flow of water into the epithelium or contact lens is probably unimportant, and a small flow in the opposite direction may actually occur.

Oxygen demands with hybrid contact lenses.

Purpose: The purpose of this study was to assess the corneal response, as measured by corneal oxygen uptake, of keratoconic corneas to SoftPerm and SynergEyes hybrid contact lenses at the central cornea, 2.0 and 4.5 mm temporal to the central cornea, and 1 mm temporal to the limbus.

Corneal oxygen uptake associated with piggyback contact lens systems.

Purpose: The purpose of this study was to determine the effects of static (without blinking) and dynamic (with blinking once every 5 seconds) wear of piggyback contact lens systems on corneal oxygen uptake.

Methods: Corneal oxygen uptake rates were measured on the right eyes of 11 human subjects by using a polarographic electrode. Measurements were made for the normal open eye and after 5 minutes of wear of 4 rigid lens materials (Dk/t 0-82.

Baseline factors predictive of incident penetrating keratoplasty in keratoconus.

Purpose: To identify baseline demographic and clinical factors associated with undergoing penetrating keratoplasty (PK) in a prospective cohort of 1,065 keratoconus patients followed for eight years in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study.

Design: Multicenter, prospective, observational cohort study.

Methods: We report the rate of PK over eight years and baseline factors predictive of PK in 1,065 patients who, at the time of study enrollment, had not undergone PK in either eye.

Factors influencing the measurement of oxygen shortfall of the human cornea: sequencing of test conditions.

Purpose: The effects of sequencing of test conditions, in this case contact lens thicknesses, on the measurement of the oxygen shortfall of human corneas were studied.

Methods: Corneal oxygen uptake rates were measured with a Clark-type polarographic electrode on the central, unanesthetized right corneas of 14 human subjects. Measurements were made under the following conditions: (1) the normal open eye; (2) after 5 min of static (without blinking) wear of each of seven rigid gas permeable lenses of seven center thicknesses (0.

Rigid gas-permeable contact lens base curve radius and transmissibility effects on corneal oxygen uptake.

Purpose: The purpose of this study is to determine the effects of rigid gas-permeable contact lens thickness, base curve radius, and material permeability on corneal hypoxic stress.

Methods: Corneal oxygen uptake rates were measured with a Clark-type polarographic electrode on the right eye of 10 human subjects for the normal open eye (air) and after 5 minutes of static wear of rigid contact lenses of four cornea-to-contact lens base curve fitting relationships: 0.2 mm steeper-than-K (STK), 0.

Interferometric imaging of the full thickness of the precorneal tear film.

A method is described for recording interference images from the full thickness of the precorneal tear film (PCTF). Simultaneous images are recorded by two video cameras. One camera responds to broadband spectral illumination and records interference from the superficial lipid layer of the tear film.

Differences in keratoconus as a function of gender.

Purpose: To characterize gender differences in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study.

Design: Observational, longitudinal study.

Methods: A total of 1209 subjects at 16 clinics.

The effects of high-Dk rigid contact lens center thickness, material permeability, and blinking on the oxygen uptake of the human cornea.

Purpose: The human corneal oxygen uptake responses associated with the static (nonblinking) and dynamic (blinking) wear of five rigid gas-permeable materials with high oxygen permeabilities were determined for three different center thicknesses and compared with the responses for the normal open eye and severe hypoxic stress (static wear of polymethylmethacrylate).

Methods: Corneal oxygen uptake rates were measured with a Clark-type polarographic electrode during two sessions with each of 10 human subjects. Measurements were made on the right eye for the normal open eye (air) and after 5 minutes of static and dynamic wear of polymethylmethacrylate and five rigid gas-permeable contact lens materials: Fluoroperm 92 (paflufocon A, Dk = 92), Fluoroperm 151 (paflufocon D, Dk = 151), 1992 Menicon SF-P (melafocon A, Dk = 102), 1995 Menicon SF-P (melafocon A, Dk = 159), and Menicon Z (tisilfocon A, Dk = 163-250).

The thickness of the tear film.

Measurements of the thickness of the pre-corneal tear film, pre-lens tear film, post-lens tear film, and the lipid layer on the surface of the tear film are summarized. Spatial and temporal variations in tear film thickness are described. Theoretical predictions of tear film thickness are discussed.

Tear exchange and oxygen reservoir effects in silicone hydrogel systems.

Purpose: The effects of oxygen reservoir and tear exchange are known for conventional hydrogel contact lenses. This study attempted to (1) confirm their presence in lenses of a silicone hydrogel (SH) material and (2) evaluate their individual and combined contributions to hypoxic relief of the cornea.

Methods: Corneal oxygen uptake rates were measured polarographically for 10 OD corneas immediately after 300-sec periods (equivalent to 60+ blink cycles) of: (1) nonblink wear of a 0 Dk/L polymethylmethacrylate (PMMA) cap lens; (2) nonblink wear of that cap lens with a SH lens inserted between it and the cornea; (3) regular blinked wear of that same lens combination; (4) nonblinked wear of the SH lens alone; and (5) normal open-eye, non-lens wear.

Enhancing RGP contact lens performance: comparing back surface options.

Background: In some cases, rigid gas-permeable (RGP) contact lenses may be the best--or only--means of refractive correction. High Dk RGP materials have markedly reduced hypoxia under those lenses. With aspheric lens back surface designs, post-lens circulation may be enhanced as well by maximizing the provision of nutrients and the clearance of metabolic by-products, toxins, and debris, while minimizing the risk of lens binding.

Between-eye asymmetry in keratoconus.

Purpose: To report baseline differences between eyes on key variables in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study cohort compared with a retrospectively assembled group of myopic contact lens wearers without ocular disease.

Methods: A total of 1,079 keratoconus patients who had not undergone a penetrating keratoplasty in either eye before their baseline visit were enrolled and examined at baseline. Records from 330 contact lens-wearing myopes were reviewed.