Accommodative response to ocular surface pain.

Clinical Relevance: The discovery of an accommodative response to ocular surface stimulation could inform clinicians and patients that optical effects may occur due to ocular discomfort and perhaps an assessment of the accommodative system after carrying out interventions impacting the ocular surface, may be warranted.

Background: There have been no previous reports evaluating the effect of noxious stimulation on accommodation. Here, the accommodative response of healthy participants after the application of noxious corneal stimulation is characterised.

Determining the spectral transmittance of photochromic contact lenses.

Purpose: This study evaluates the spectral transmission of photochromic contact lenses.

Method: A custom built photochromic filter transmission testing device (ICS photochromic bench) was developed to measure the spectral transmission of light adaptive filters. The spectral properties of seven contact lenses were measured using the ICS photochromic bench at 23⁰C and 35⁰C in their exposed (darkening) state at time points 0 s, 45 s, 90 s, and 15 min.

Detectability and Bias Indices of Pneumatic Corneal Stimuli Using Signal Detection Theory.

Purpose: To evaluate the feasibility of using signal detection theory (SDT) in estimating criterion and detectability indices for corneal pneumatic stimuli and test corneal psychophysical data against linking hypotheses from nonprimate physiology using Bayesian analysis.

Methods: Corneal pneumatic stimuli were delivered using the Waterloo Belmonte esthesiometer. Corneal thresholds were estimated in 30 asymptomatic participants and 1.

Role of diurnal variation of corneal sensory processing in contact lens discomfort.

Purpose: To examine the diurnal variation of corneal threshold and suprathreshold sensory processing, symptoms, and tear secretion in symptomatic and asymptomatic contact lens (CL) wearers and controls.

Methods: 26 symptomatic and 25 asymptomatic CL wearers and 15 asymptomatic non-CL wearing controls participated. Cooling thresholds, symptoms and tear meniscus height (TMH) were measured on each of 3 measurement days (random order) on the following schedules; Day-1 within 1 h of awakening (Baseline) and 3, 6 and 9 h later, Day-2 baseline and 9 h later (CLs worn in CL group) and Day-3 baseline and 9 h later.

Pupil response to noxious corneal stimulation.

Purpose: Ocular somatosensory-autonomic reflexes play critical roles in maintaining homeostasis of the eye. The purpose of this study was to investigate the pupil response to nociceptive corneal stimuli.

Methods: A Waterloo-Belmonte pneumatic esthesiometer was used to determine detection thresholds and randomly deliver mechanical and chemical stimuli from levels of detection threshold to twice the threshold in 50% steps to the central cornea of 15 healthy subjects.

Changes in Corneal Detection Thresholds After Repeated Tear Film Instability.

Purpose: To use a human-based model to study the effects of repeated tear film instability on corneal detection thresholds to cold, mechanical, and chemical stimuli.

Methods: Twenty-five subjects participated in three study visits. A computer-controlled Belmonte esthesiometer was used to estimate corneal detection thresholds to cold, mechanical, and chemical stimuli before, after, and 30 minutes following 10 consecutive sustained tear exposure (STARE) trials.

A Method to Calibrate the Carbon Dioxide (Chemical) Stimuli of Pneumatic Esthesiometer Externally.

Purpose: To determine the feasibility of using a portable carbon dioxide (CO) sensor to calibrate a pneumatic esthesiometer and then to calibrate the chemical stimuli.

Methods: The chemical stimuli in ocular surface experiments are combinations of medical air and added CO (%CO). These stimuli were calibrated using a portable CO sensor (COZIR CM-0041) and data logger, delivered for 100 seconds by using the Waterloo Belmonte esthesiometer.

Effects of Tear Film Instability on Sensory Responses to Corneal Cold, Mechanical, and Chemical Stimuli.

Purpose: To investigate the effects of tear film instability (TFI) induced by sustained tear exposure (STARE) on sensory responses to corneal cold, mechanical, and chemical stimuli.

Methods: Fifteen normal subjects were enrolled. TFI was induced during 10 repeated trials of STARE.

Conjunctival Redness Response to Corneal Stimulation.

Significance: The conjunctiva is an integral component of the ocular surface, and its vasculature forms a terminal vascular bed of the human internal carotid artery. No research on the response of conjunctival vasculature to ocular surface stimulation exists; however, it is essential to understand the local physiological and pathological responses to such a stimulus.

Purpose: The purpose of this study was to characterize the ocular redness levels in healthy participants after the application of noxious corneal stimulation.

Mixed Model Analysis of Between-Subject Variability in Overnight Corneal Swelling and Deswelling With Silicone Hydrogel Lenses.

Purpose: To model between subject variability of corneal swelling (CS) and deswelling after overnight wear of silicone hydrogel (SiHy) contact lenses.

Methods: A total of 29 neophyte subjects wore 12 SiHy lenses with central transmissibility range of 31 to 211 Dk/t units on separate nights, in random order, and on one eye only. The contralateral eye served as the control.

Influence of Vision on Ocular Comfort Ratings.

Purpose: To evaluate the influence of blur on ocular comfort while systematically manipulating vision using habitual refractive correction, induced spatial blur, dioptric defocus, and under the absence of visual structure.

Methods: Twenty emmetropic subjects rated vision, ocular comfort, and other sensations (burning, itching, and warmth) under clear viewing condition, spatial blur, and dioptric defocus, each lasting for 5 min. During each condition, subjects viewed digital targets projected from a distance of 3 m, and vision and ocular sensations were rated using magnitude estimation.

Optical edge effects create conjunctival indentation thickness artefacts.

Purpose: Conjunctival compression observed in ultrahigh resolution optical coherence tomography (UHR-OCT) images of contact lens edges could be actual tissue alteration, may be an optical artefact arising from the difference between the refractive indexes of the lens material and the conjunctival tissue, or could be a combination of the two. The purpose of this study is to image the artefact with contact lenses on a non-biological (non-indentable) medium and to determine the origins of the observed conjunctival compression.

Methods: Two-dimensional cross-sectional images of the edges of a selection of marketed silicone hydrogel and hydrogel lenses (refractive index ranging from 1.

Impact of Blur on Suprathreshold Scaling of Ocular Discomfort.

Purpose: To examine the suprathreshold scaling of pneumatic stimuli, and the ratings of discomfort and intensity under clear and defocused visual conditions.

Methods: Twenty-one participants rated sensory intensity and discomfort of a series of mechanical stimuli from a pneumatic esthesiometer, using a 0 to 100 numerical scale under clear and defocused visual conditions. Esthesiometry was performed on one eye while the fellow eye viewed a 3-m distant 6/60 target through a trial lens.

Overnight corneal swelling with high and low powered silicone hydrogel lenses.

Purpose: To compare central corneal swelling after eight hours of sleep in eyes wearing four different silicone hydrogel lenses with three different powers.

Methods: Twenty-nine neophyte subjects wore lotrafilcon A (Dk, 140), balafilcon A (Dk, 91), galyfilcon A (Dk, 60) and senofilcon A (Dk, 103) lenses in powers -3.00, -10.

Measurement of difference thresholds on the ocular surface.

Purpose: To establish difference thresholds of the central cornea and compare thresholds between contact lens wearers and noncontact lens wearers.

Methods: Mechanical sensitivity of the central cornea was determined in 12 lens wearers and 12 nonlens wearers using a modified Belmonte pneumatic esthesiometer and method of limits. Then, a series of systematically increasing stimuli were presented, with the first stimulus being 25% less than threshold.

Grading bulbar redness using cross-calibrated clinical grading scales.

Purpose: To determine the between-scale agreement of grading estimates obtained with cross-calibrated McMonnies/Chapman-Davies (MC-D), Institute for Eye Research (IER), Efron, and Validated Bulbar Redness (VBR) grading scales.

Methods: Modified reference images of each grading scale were positioned on a desk according to their perceived redness (within a 0 to 100 range) as determined in a previous psychophysical scaling experiment. Ten observers were asked to represent perceived bulbar redness of 16 sample images by placing them, one at a time, relative to the reference images of each scale.

A role of corneal mechanical adaptation in contact lens-related dry eye symptoms.

Purpose: To compare corneal mechanical adaptation measured psychophysically in contact lens wearers with or without dry eye symptoms.

Methods: Two groups of contact lens wearers were recruited. One group (symptomatic) consisted of subjects with dry eye symptoms (according to the subjective evaluation of symptom of dryness [SeSoD] questionnaire).

Effects of silicone hydrogel contact lens wear on ocular surface sensitivity to tactile, pneumatic mechanical, and chemical stimulation.

Purpose: To determine the effects of silicone hydrogel lens wear and lens-solution interactions on ocular surface sensitivity.

Methods: Forty-eight adapted lens wearers completed the study, which comprised two phases. Phase 1 included habitual lens wear, no lens wear (7 ± 3 days), and balafilcon A lenses (PV; PureVision; Bausch & Lomb, Rochester, NY) with a hydrogen peroxide-based regimen for 2 weeks; phase 2 included wear of PV with the use of a multipurpose solution containing either polyhexamethylene-biguanide (PHMB) or Polyquad/Aldox (Alcon Laboratories, Fort Worth, TX) preservative, each for 1 week, with a 2-week washout period between solutions.

Interaction of corneal nociceptive stimulation and lacrimal secretion.

Purpose: To investigate the interaction between corneal stimuli at different positions and tear secretion and to establish relationships between nociceptive stimuli detection thresholds and stimulated tearing.

Methods: Using a computerized Belmonte-esthesiometer, mechanical and chemical stimuli, from 0% to 200% of the threshold in 50% steps, were delivered (in random order) to the central and peripheral (approximately 2-mm inside the limbus) cornea during four separate sessions to 15 subjects. Immediately after each stimulus, tear meniscus height (TMH) was measured using optical coherence tomography to quantify the amount of lacrimal secretion, and subjects reported whether they felt tears starting to accumulate in their eyes.

Swelling of the human cornea revealed by high-speed, ultrahigh-resolution optical coherence tomography.

Purpose: To evaluate the change in thickness of the anterior, stromal, and posterior corneal laminae in response to hypoxia-induced corneal swelling, by means of ultrahigh-resolution optical coherence tomography (UHR-OCT).

Methods: A UHR-OCT system, operating in the 1060-nm range, was used to acquire in vivo cross-sectional images of human cornea with a 3.2x10-microm (axial x lateral) resolution in corneal tissue.

The conversion of bulbar redness grades using psychophysical scaling.

Purpose: To use psychophysical scaling to investigate if the inclusion of reference anchors affected the perceived redness of the reference images of four bulbar redness grading scales and to convert grades between scales.

Methods: Ten participants were asked to arrange printed copies of the McMonnies/Chapman-Davies (6), IER (4), and Efron (5) grading scale images relative to each other, using the stationary but unlabeled 10, 30, 50, 70, and 90 reference images of the validated bulbar redness scale as additional anchors within a given 0 (minimum) to 100 (maximum) redness range (anchored scaling). The position of each image was averaged across observers to represent its perceived redness within this range.

Human corneal adaptation to mechanical, cooling, and chemical stimuli.

Purpose: To psychophysically investigate adaptation in human corneas using the Belmonte pneumatic esthesiometer.

Methods: Twenty, 8, and 20 healthy subjects were enrolled in the mechanical, cool, and chemical experiments, respectively. Thresholds were estimated using an ascending method of limits and three intensities (subthreshold, threshold, and suprathreshold, in random order) were each presented 10 or 20 times, and subjects scaled the intensity of the stimuli (0-4 [no stimulus to very intense stimulus]).

The perceived bulbar redness of clinical grading scales.

Purpose: To use a psychophysical scaling method to estimate the perceived redness of reference images of the McMonnies and Chapman-Davies (six reference levels), Institute for Eye Research (four), Efron (five), and Validated Bulbar Redness (five) bulbar redness grading scales.

Methods: Regions of interest were cropped out of the grading scale reference images; three separate image sets (color, grayscale, and binarized) were created for each scale, combining to a total of 20 images per image set. Ten naïve observers were asked to arrange printed copies of the 20 images per image set across a distance of 1.

The interblink interval I: the relationship between sensation intensity and tear film disruption.

Purpose: To find the relationship between tear film drying and sensation during the interblink period.

Methods: One eye was taped shut, and after a blink the subjects were required to keep the other eye open. Digital video images of the ocular surface (with fluorescein) were obtained using a slit lamp biomicroscope while 23 subjects rated the intensity of the ocular surface sensation by adjusting a one-turn potentiometer to represent the strength of the sensation.