Key factors in the subjective and objective assessment of conjunctival erythema.

PURPOSE: To establish objectively measurable characteristics of the conjunctival vasculature that correspond with the judgment of erythema by human observers. METHODS: Color images of bulbar conjunctiva from 21 subjects were digitally analyzed to extract the following variables characteristic of the scene: vessel width (W), number of vessels (V), proportion of area occupied by vessels (PA), relative redness both in vessels (RRV) and in the whole image (RRI), red-green difference both in vessels (RGV) and in the whole image (RGI), red-blue difference both in vessels (RBV) and in the whole image (RBI), and red hue value (RHV). These data were compared with subjective judgments by a panel of seven trained observers who independently rated erythema in the same images, using a 0 to 4 scale with decimal interpolation between grades. RESULTS: Correlation analysis indicated significant associations (P<0.05) between the mean response of the human observers and all the objective variables except RHV. Associations with the morphometric variables PA (R2 = 0.93) and V(R2 = 0.90) were markedly stronger than for the best colorimetric variable RBV (R2 = 0.62). CONCLUSIONS: Judgments of erythema made by human observers do not rely primarily on color but can be closely approximated by a univariate, linear model involving only the proportion of the scene occupied by vessels. Under the conditions of this study, grading of erythema by trained observers can be considered to constitute measurement to at least an interval level.

Corneal and conjunctival sensitivity to air stimuli.

AIMS: To determine the repeatability of ocular surface sensitivity to mechanical stimulation using air stimuli and the effect of contact lens (CL) wear on sensitivity. METHODS: Repeatability: 14 subjects (24-39 years) participated. Mechanical sensitivity to warmed (34 degrees C) and ambient (20 degrees C) air was measured for the central cornea (CC), inferior cornea (IC), and inferior conjunctiva (ICON). Measurements were taken on 12 days; six morning and six afternoon measurements. Differences between sites, time of day, and stimulus temperature were evaluated. CL wear: 10 subjects (22-30 years) participated. Measurements were taken at the same time of day, either following no wear, wear of a CL of oxygen permeability [Dk] of 28 x 10(-9) [cm/s][ml O(2)/ml mm Hg] or wear of a CL of Dk 140 x 10(-9) [cm/s][ml O(2)/ml mm Hg]. Differences between sites and wear conditions were evaluated. RESULTS: Repeatability: Sensitivity varied between sites (p<0.01), time of day (p<0.05), and stimulus temperatures (p<0.01). There were no significant differences between days. Mean thresholds for eye temperature stimuli were; CC 64.4 (SD 28.6) ml/min; IC 84.6 (40.0) ml/min; ICON 120.6 (40.4) ml/min and for ambient temperature stimuli were CC 53.9 (16.0) ml/min, IC 59.0 (20.0) ml/min; ICON 72.6 (43.7) ml/min. CL wear: Sensitivity varied between sites and wear conditions (p<0.05). Conjunctival sensitivity was increased after wear of highly oxygen permeable CLs but unaffected by wear of low oxygen permeable CLs. CONCLUSIONS: The prototype gas aesthesiometer is able to repeatably measure ocular surface sensitivity and measurements are consistent with previously reported techniques.

Inter-ocular characteristics of the pre-contact lens tear film.

PURPOSE: To establish whether the status of the pre-contact lens tear film as indicated by standard, clinical observational techniques is affected by moderate stimulation of the contralateral eye. METHODS: Four indicators of tear film behavior, lipid layer appearance, amount of debris, inferior meniscus height and non-invasive tear break up time (NIBUT) were monitored in ten subjects before and during 30 minutes of monocular pHEMA contact lens wear. Concurrently, the contralateral eye was either subjected to moderate irritation by means of a silicone elastomer contact lens, or remained unstimulated. Data were compared, between the stimulated and unstimulated states to identify evidence of contralateral treatment effects. RESULTS: After 30 minutes, maximum contralateral differences between the unstimulated and stimulated conditions were 1 grade for both lipid layer appearance and debris, 0.1 mm for meniscus height and 4 secs for NIBUT. CONCLUSIONS: The magnitudes of contralateral effects induced by moderate, monocular irritation were comparable with the within-subject variabilities associated with these indicators of tear film behavior.

High-oxygen-transmissibility soft contact lenses do not induce limbal hyperaemia.

PURPOSE: To establish the temporal sequence of limbal hyperaemia in humans without contact-lens wear and during conventional and highly oxygen-permeable soft-contact-lens wear. METHODS: Two, 16-h, non-dispensing clinical studies were conducted, each incorporating 8 h of open eye with normal blinking, followed by 8 h of eye closure during sleep. In the first study, six non-habitual contact-lens wearers did not wear contact lenses. In the second study, the same subjects were each randomly assigned, in a double-masked fashion, to wear a conventional, thin, 38% water, pHEMA soft contact lens (SCL) in one eye and an experimental high Dk (EHD), 20%-water soft contact lens in the other. Limbal redness (LR) was graded, using a 0-4 scale with decimalised subdivisions, at baseline and after 4, 8 and 16 h. ANOVA was applied to the data, and the level for statistical significance was set at p < or = 0.005. RESULTS: In the non-wearing eye, LR changes averaged 0.2 +/- 0.2 and 0.4 +/- 0.2 grades at 4 and 16 h, respectively (inferior quadrant). The corresponding values for SCL wear were 1.0 +/- 0.6 and 1.1 +/- 0.6, while for EHD wear they were 0.2 +/- 0.4 and 0.5 +/- 0.5. Both for the normal eye and those wearing EHD lenses, increases in LR were significant only during eye closure (p < 0.005). During SCL wear, significant and larger LR increases were seen after 4 h open eye wear (p < 0.005), with only relatively small further changes being observed over the next 12 h. CONCLUSIONS: SCL wear induces a marked increase in limbal hyperaemia during open-eye wear, which is not seen either in the no lens situation or when EHD lenses are worn. The pattern of limbal hyperaemia for both the open and closed eyes during EHD lens wear is very similar to that for the no-lens situation. The mechanism whereby SCL induces excess limbal hyperaemia has not been absolutely established, but it may involve local hypoxia.

Repeatability and comparison of visual analogue and numerical rating scales in the assessment of visual quality.

The repeatabilities of both the visual analogue scale (VAS) and numerical rating scale (NRS) as methods of assessing visual quality (VQ) were estimated by obtaining three replicated responses from each of a group of nine normal subjects who viewed a standardized scene under conditions of controlled refractive blur. In both cases, repeatability was highest in the absence of blur but fell markedly as increasing amounts of visual decrement were induced. Coefficients of reproducibility ranged from 4.1 to 36.0 for VASs; and from 1.2 to 34.9 for NRSs. Except where VQ was high, both types showed generally poor repeatability. When the data were used to compare the two methods, no consistent bias was found and agreement was good for high VQ levels. The NRS offers a reasonable alternative to the VAS as a method of assessing subjective VQ.

Simultaneous vision bifocal contact lenses: a comparative assessment of the in vitro optical performance.

We measured the modulation transfer functions (MTF's) of five simultaneous vision bifocal contact lenses: center-near (Alges, University Optical Products), center-distance (BiSoft, CIBA Vision), diffractive rigid gas-permeable (Diffrax, Pilkington Barnes-Hind), diffractive hydrogel (Hydron Echelon, Allergan), and varifocal center-near (PS-45, G. Nissel). MTF's were measured at various aperture sizes (1 to 7 mm) and at a wavelength of 546 nm. The soft diffractive bifocal MTF's were measured at various wavelengths. The results tended to confirm previous theoretical calculations. The optical performance of the concentric designs was highly sensitive to variations in aperture size. The optical performance of both the rigid and soft diffractive lenses was largely (but not entirely) independent of aperture size. The varifocal lens was sensitive to changes in aperture size with respect to both optical quality and optimal focus.