Variations in corneal sensitivity with hydrogel contact lenses

Association of ocular surface and meibomian gland alterations with silicone hydrogel contact lens wear

PURPOSE

To evaluate silicone hydrogel contact lens (SH-CL) effects on the meibomian glands, corneal structure, and ocular surface parameters.

METHODS

Fifty SH-CL wearers for at least 6 months, and 50 sex and age-matched control subjects were recruited for this cross-sectional study. Visual display terminal (VDT) work and CL wear duration were questioned, ocular surface and tear functions were evaluated using OSDI questionnaire, tear break-up time (TBUT), corneal fluorescein staining, and Schirmer test. Corneal sensitivity was measured with Cochet-Bonnet aesthesiometry. Meibography and in vivo confocal microscopy (IVCM) were performed to evaluate meibomian glands and corneal structure. Intergroup comparisons were made using the Chi-square test, Wilcoxon test, or Kruskal-Wallis test.

RESULTS

In the CL group, TBUT was shorter (P = 0.01), corneal fluorescein staining (P = 0.04), OSDI scores (P < 0.001), and meiboscores (P < 0.001) were higher than the control group. The biomicroscopic evaluation revealed meibomian gland dysfunction (MGD) in 34 % of the CL group and 20 % of the control group, which was not statistically significant (P > 0.05). IVCM showed that endothelial cell density was lower (P = 0.01) and polymegethism was higher (P < 0.001) in the CL group. Subbasal nerve density and corneal sensitivity measurements were similar in the two groups (P > 0.05). The longer VDT work duration was associated with increased CFS in the CL group (P = 0.05).

CONCLUSION

The results showed that SH-CL wear increased dry eye symptoms and ocular discomfort, especially in longer VDT work duration. Meibography revealed significantly worse results in SH-CL wearers. SH-CL-related ocular discomfort seems to be more associated with MGD rather than neurosensorial alterations.

Corneal sensitivity in silicone hydrogel and rigid gas permeable contact lens wear

PURPOSE

The aim of this prospective cross-sectional cohort study was to test the effect of silicone hydrogel (SH) and rigid gas permeable (RGP) contact lens (CL) wear on corneal sensitivity, applying the new Swiss Liquid Jet Aesthesiometer for Corneal Sensitivity (SLACS) and the Cochet-Bonnet (CB) aesthesiometer, based on subject feedback (psychophysical method).

METHODS

Participants were recruited for three equally large groups: Group A (SH CL), Group B (RGP CL) and Group C (non-CL wearers). Inclusion criteria were healthy eyes and OSDI ≤ 13. Corneal sensory thresholds were determined twice during two visits, with aid of SLACS and CB.

RESULTS

96 participants completed the study (n = 33 in groups A and C, n = 30 in group B); average age in group A: 27.42 ± 6.83 years, group B: 36.90 ± 9.68 years and group C: 26.06 ± 6.19 years. No statistically significant difference in corneal sensitivity was observed between the three groups for either method (p = 0.302 for SLACS, p = 0.266 for CB; Kruskal-Wallis rank sum test). Higher CSTs were obtained for males than for females in both CL groups with SLACS, and with CB only in the RGP CL group (p = 0.041 in Group A, p = 0.006 in Group B with SLACS; p = 0.041 in Group B with CB; bootstrap analysis with age correction and gender balancing). No correlation was observed between CL comfort and corneal sensitivity for neither method applied (for SLACS r = 0.097 and p = 0.51, for CB r = 0.17 and p = 0.15; robust linear mixed model).

CONCLUSIONS

No difference in corneal sensitivity with CL compared to non-CL wear was noted in this study. However, lower levels of corneal sensitivity were observed in the male CL groups, warranting further investigation.

Short-Term effects of ambient ozone on the risk of conjunctivitis outpatient visits: a time-series analysis in Pudong New Area, Shanghai

To date, the relationship between conjunctivitis and air pollutants has been widely concerned, but the conclusions are not very unified. This study aims to explore the short-term effects of ambient ozone (O₃) on the conjunctivitis outpatient visits in Pudong New Area, Shanghai. A quasi-Poisson model combined with the distributed lag nonlinear model (DLNM) was performed to study the short-term effects of O₃ on the risk of outpatient visits for conjunctivitis, after controlling the effects of temperature, relative humidity and wind speed. Taking the median concentration of O₃ as a reference, the moderate high O₃ (75th percentile) showed the largest effect estimates for single and cumulative lag effects at lag 4 (RR 1.013, 95% confidence interval [CI] 1.006-1.019) and lag 0-10 (RR 1.075, 95%CI 1.025-1.128), respectively. Our study suggested that the moderate high O₃ increased the chances of conjunctivitis outpatient visits and had an evident lag effect.

Association between short-term exposure to ambient nitrogen dioxide and the risk of conjunctivitis in Hefei, China: A time-series analysis

BACKGROUND

Conjunctivitis, one of the most common ocular surface diseases, can be caused by many contributors. However, the important role of air pollution has been inadequately evaluated, particularly in countries with poor air quality. This study aims to explore the possible association of short-term ambient nitrogen dioxide (NO₂) exposure with the risk of outpatient visits for conjunctivitis.

METHODS

A total of 43,462 conjunctivitis patients from January 1, 2014 to December 31, 2018 were identified from the Department of Ophthalmology of The Second Affiliated Hospital of Anhui Medical University, Hefei, China. Such data were linked to the daily mean concentration of NO₂ at ten fixed air quality monitoring stations. A distributed lag nonlinear model (DLNM) combined with a quasi-Poisson generalized linear regression model was employed to assess the association between NO₂ exposure and the risk of outpatient visits for conjunctivitis. Stratified analyses were also performed on the basis of gender, age group and season.

RESULTS

The association of NO₂ exposure with the risk of outpatient visits for conjunctivitis was statistically significant. In the single-day lags (lag 0 to lag 11) analysis, the largest effect estimates were observed at lag 0. In the moving average exposure lags (lag 0-1 to lag 0-11) analysis, the cumulative effects were stronger than the single-day lag effects. The stratified analyses suggested that the effect of NO₂ exposure was more pronounced in females and patients aged 19-65 years and in the cold season.

CONCLUSIONS

This study confirms the evidence that short-term NO₂ exposure is associated with an increased risk of conjunctivitis outpatient visits. Our research encourages individuals to avoid outdoor activities on severe air pollution days and the government is obliged to adopt more stringent environmental policies to alleviate the effects of air pollution on human health, particularly for individuals at risk of developing conjunctivitis.

CLEAR - Effect of contact lens materials and designs on the anatomy and physiology of the eye

This paper outlines changes to the ocular surface caused by contact lenses and their degree of clinical significance. Substantial research and development to improve oxygen permeability of rigid and soft contact lenses has meant that in many countries the issues caused by hypoxia to the ocular surface have largely been negated. The ability of contact lenses to change the axial growth characteristics of the globe is being utilised to help reduce the myopia pandemic and several studies and meta-analyses have shown that wearing orthokeratology lenses or soft multifocal contact lenses can reduce axial length growth (and hence myopia). However, effects on blinking, ptosis, the function of Meibomian glands, fluorescein and lissamine green staining of the conjunctiva and cornea, production of lid-parallel conjunctival folds and lid wiper epitheliopathy have received less research attention. Contact lens wear produces a subclinical inflammatory response manifested by increases in the number of dendritiform cells in the conjunctiva, cornea and limbus. Papillary conjunctivitis is also a complication of all types of contact lenses. Changes to wear schedule (daily disposable from overnight wear) or lens materials (hydrogel from SiHy) can reduce papillary conjunctivitis, but the effect of such changes on dendritic cell migration needs further study. These changes may be associated with decreased comfort but confirmatory studies are needed. Contact lenses can affect the sensitivity of the ocular surface to mechanical stimulation, but whether these changes affect comfort requires further investigation. In conclusion, there have been changes to lens materials, design and wear schedules over the past 20+ years that have improved their safety and seen the development of lenses that can reduce the myopia development. However, several changes to the ocular surface still occur and warrant further research effort in order to optimise the lens wearing experience.

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. Magnitudes estimates for threshold-scaled suprathreshold stimuli were also estimated on Day-3. Data were analyzed using mixed models and repeated measures ANOVA.

RESULTS

Cooling thresholds for the symptomatic group were lower and decreased over Day-1 (p < 0.008) and after 8 h of CL wear on Day-2 (p < 0.001) and were paralleled by increased symptoms (all p < 0.001), whereas minimal variations were found in the asymptomatic and control groups. Magnitude estimates for suprathreshold stimuli were higher (p ≤ 0.002) in the symptomatic group but did not differ significantly over the day. TMH varied little over time and was lower in the symptomatic group, but the difference was not statistically significant.

CONCLUSION

Corneal sensitivity and symptoms, but not TMH, increased diurnally irrespective of CL wear in symptomatic CL wearers. These results reveal the essential role of neurosensory abnormalities in CL discomfort and suggest involvement of a central mechanism in the diurnally increased symptoms of these patients.

Global Associations of Air Pollution and Conjunctivitis Diseases: A Systematic Review and Meta-Analysis

(1) Background: As the most common eye disease diagnosed in emergency departments, conjunctivitis has caused serious health and economic burdens worldwide. However, whether air pollution may be a risk factor for conjunctivitis is still inconsistent among current evidence. (2) Methods: We searched the literature on the relationship between air pollution and conjunctivitis in multiple English databases before 18 March 2019. Meta-analysis, meta-regression, and funnel plots were used to integrate the data, identify the sources of bias, and determine the publication bias, respectively. (3) Results: A total of 2450 papers were found, 12 of which were finally included. The pooled relative risk for each 10 μg/m³ increase of air pollution on conjunctivitis was 1.0006 (95%CI: 0.9993–1.0019) for CO, 1.0287 (1.0120–1.0457) for NO₂, 1.0089 (1.0030–1.0149) for O₃, 1.0004 (0.9976–1.0032) for PM_2.5, 1.0033 (0.9982–1.0083) for PM₁₀, and 1.0045 (0.9908–1.0185) for SO₂. In the subgroup, PM_2.5 and O₃ had a greater impact on conjunctivitis risk in women than in men, and people <18 years old than those ≥18 years old. Relative humidity significantly modified the risk of O₃ on conjunctivitis (p = 0.023), explaining 45% of the between-study heterogeneity. (4) Conclusion: Globally, air pollution has considerable health risks for conjunctivitis. Females and the youth were more vulnerable to PM_2.5, NO₂, and O₃. Reductions of air pollution levels are still warranted to protect the vulnerable populations.

Sensory Adaptation to Silicone Hydrogel Contact Lens Wear Is Not Associated With Alterations in the Corneal Subbasal Nerve Plexus

PURPOSE

To evaluate corneal subbasal nerve alterations in contact lens (CL)-naive silicone hydrogel CL wearers and to investigate the relationship between structural subbasal nerve changes with corneal sensitivity.

METHODS

Twenty eyes of 20 neophyte daily silicone hydrogel CL wearers and 20 eyes of age-matched control subjects were recruited for this prospective longitudinal study. Corneal subbasal nerve densities were evaluated using in vivo confocal microscopy. Central corneal tactile sensitivity was measured using Cochet-Bonnet esthesiometers. In vivo confocal microscopy and Cochet-Bonnet esthesiometry were performed before and at the 6-month time point after the initiation of CL wear. Two-way repeated measures analysis of variance, χ, and Wilcoxon signed-rank tests were used for statistical analyses.

RESULTS

The mean ages of CL users and control subjects were 21.8 ± 1.8 years (range = 19-24 years) and 21.5 ± 2.3 years (range = 20-24 years), respectively (P = 0.579). Compared with their baseline values, there were no significant changes at the 6-month follow-up period in the mean total subbasal nerve fiber length (2266.6 ± 414.6 vs. 2277.9 ± 405.0 μm/frame; P = 0.432), mean total subbasal nerve branch density (10.4 ± 1.5 vs. 10.5 ± 1.3 nerves/frame; P = 0.655), or the mean long nerve fiber density (4.7 ± 0.7 vs. 4.8 ± 0.7 nerves/frame; P = 0.564) of CL users. Mechanical corneal sensitivity remained unaltered during the 6-month period in CL users (11.2 ± 0.5 vs. 11.2 ± 0.5; P = 1.000). No significant changes were observed in the subbasal nerve plexus or corneal tactile sensitivity of the control subjects during the study interval.

CONCLUSIONS

Sensory adaptation to CL wear is not mediated through attenuation of the subbasal nerve or reduction of corneal tactile sensitivity in CL-naive users.

Relationship Between the Degree of Iris Pigmentation and Corneal Sensitivity to a Cooling Stimulus

PURPOSE

To explore the relationship between the degree of iris pigmentation and corneal sensitivity threshold (CST) on a variety of different ethnicities, using the air-jet noncontact corneal aesthesiometer and by applying a consistent method of subject iris pigmentation classification.

METHODS

A total of 200 subjects (mean age 23.7 ± 3.1 years, 127 women) participated in this clinical cross-sectional study: 100 whites, 40 Asians, 40 Chinese, and 20 Afro-Caribbeans. CST was assessed within the central cornea using a noncontact corneal aesthesiometer, and the degree of iris pigmentation of each subject was noted according to the Seddon method using a set of graded photographs of iris pigmentation (grades 1-5). Inclusion criteria were absence of ocular disease including dry eye, no contact lens wear, and no use of artificial tears. Statistical testing between ethnicities was made by the pairwise t test with Holm adjustment, and a linear model was set up to analyze the effects of ethnicity and iris grade.

RESULTS

A moderate trend for increasing CST with increasing iris pigmentation grade for all ethnicities was observed (R = 0.46; P < 0.0001), with CST changing from 0.66 ± 0.16 mbars for grade 1, 0.74 ± 0.18 mbars for grade 2, 0.86 ± 0.31 mbars for grade 3, 0.85 ± 0.32 mbars for grade 4, and 1.08 ± 0.40 mbars for grade 5. This correlation was stronger within the white group, representing the only ethnicity with all iris pigmentation grades (R = 0.50; P < 0.0001).

CONCLUSIONS

There is a moderate relationship between corneal sensitivity and the degree of iris pigmentation, with sensitivity increasing as iris pigmentation decreases. This relationship is stronger within whites.

Efficacy of Rebamipide Instillation for Contact Lens Discomfort With Dry Eye

Objective:

To examine the effects of rebamipide ophthalmic solution on the symptoms, signs, and cytokine concentrations in tear fluid among soft contact lens (SCL) wearers with Dry eye disease (DED).

Methods:

From November 2015 to June 2017, this open-label, single-arm study examined 40 eyes of 20 SCL wearers with DED who had been using daily disposable SCLs for >3 months (mean age, 30.0±8.33 years; range, 20–47 years). Signs, symptoms, and cytokine concentrations were assessed before and 4 weeks after starting 2% rebamipide ophthalmic solution 4 times/day. Dry eye disease was diagnosed according to: compromised tear dynamics (Schirmer test ≤5 mm or tear break-up time (TBUT) ≤5 sec); ocular surface abnormalities (positive vital staining with fluorescein or lissamine green); and presence of symptoms. Touch thresholds using a Cochet-Bonnet anesthesiometer were also determined for the cornea and conjunctivae. Symptoms were assessed using the 12-item Ocular Surface Disease Index questionnaire. Concentrations of cytokines in tear fluid were measured.

Results:

Significant improvements in signs were seen for TBUT, surface abnormalities, and touch thresholds. Ocular Surface Disease Index scores likewise improved significantly in all the 12 items. Of the cytokines measured, only interleukin-1β, interleukin-8, and monocyte chemotactic protein-1 were found in ≥60% of tear samples, with no significant differences in concentrations before and after rebamipide use.

Conclusions:

Rebamipide significantly improved all signs and symptoms in patients with DED who wore daily disposable SCLs. Rebamipide is effective for DED treatment with SCL wear.

Lid wiper epitheliopathy

Some recent research has resulted in a hypothesis that there is a common 'lid wiper' region that is apposite to the ocular surface or anterior lens surface (where contact lenses are worn), responsible for spreading tears during blinking. In the upper eyelid, it extends about 0.6 mm from the crest of the sharp posterior (inner) lid border (i.e. the mucocutaneous junction, or line of Marx) to the subtarsal fold superiorly and from the medial upper punctum to the lateral canthus horizontally. Histologically, it is seen as an epithelial elevation comprising of stratified epithelium with a transitional conjunctival structure of (moving posteriorly) squamous cells then cuboidal cells, with some parakeratinised cells and goblet cells. Lid wiper epitheliopathy (LWE) denotes staining of the lid wiper observed after instillation of dyes such as fluorescein, rose bengal or lissamine green. There have been some reports of higher rates of LWE in dry eye patients and contact lens wearers, but others have failed to find such associations. The primary cause of LWE is thought to be increased friction between the lid wiper and ocular or anterior contact lens surface due to inadequate lubrication, which could be caused by dry eye and may be exacerbated by factors such as abnormal blinking patterns, poor contact lens surface lubricity and adverse environmental influences. Recent evidence suggests that LWE is associated with sub-clinical inflammation. LWE has the potential to provide the missing mechanistic link between clinical observation and symptoms associated with dry eye and contact lens wear. Clinical and fundamental research into LWE is still in its infancy and in many instances equivocal; however, it is an idea that provides a potentially important new avenue for further investigation of anterior eye discomfort associated with ocular dryness and contact lens wear.

Corneal sensitivity with contact lenses of different mechanical properties

PURPOSE

To examine the changes in corneal sensitivity after overnight wear of contact lenses with different mechanical properties.

METHODS

Twenty young-adult subjects wore a silicone hydrogel, rigid gas-permeable, or orthokeratology (OK) contact lens in randomized order for a single night of wear in the right eye only. All lenses were matched in Dk/t (∼46 ISO Fatt). Changes in corneal apical radius r(o), asphericity Q, and corneal refractive power (Medmont E300) were measured. Changes in central corneal sensitivity were also measured by a masked investigator using two instruments: Cochet-Bonnet (COBO) aesthesiometer and Non-Contact Corneal Aesthesiometer (NCCA).

RESULTS

There were significant differences in corneal topographic change from baseline between the lens types for r(o), Q, and corneal refractive power. There were also significant differences in the change from baseline (mean ± SD) in corneal sensitivity between lens types using the COBO (silicone hydrogel, 0.02 ± 0.17 g/mm(2); rigid gas-permeable, 0.03 ± 0.20 g/mm; OK, 0.22 ± 0.33 g/mm(2)). A significant increase in threshold from baseline was only seen in the OK lenses (p = 0.006). There was no change in sensitivity thresholds from baseline for any lens type using the NCCA (p > 0.05).

CONCLUSIONS

Central corneal sensitivity is reduced after a single overnight wear of OK lenses, as measured using the COBO aesthesiometer. This suggests that the mechanical force exerted by contact lenses may influence corneal sensitivity.

The TFOS International Workshop on Contact Lens Discomfort: report of the subcommittee on neurobiology

This report characterizes the neurobiology of the ocular surface and highlights relevant mechanisms that may underpin contact lens-related discomfort. While there is limited evidence for the mechanisms involved in contact lens-related discomfort, neurobiological mechanisms in dry eye disease, the inflammatory pathway, the effect of hyperosmolarity on ocular surface nociceptors, and subsequent sensory processing of ocular pain and discomfort have been at least partly elucidated and are presented herein to provide insight in this new arena. The stimulus to the ocular surface from a contact lens is likely to be complex and multifactorial, including components of osmolarity, solution effects, desiccation, thermal effects, inflammation, friction, and mechanical stimulation. Sensory input will arise from stimulation of the lid margin, palpebral and bulbar conjunctiva, and the cornea.

Factors affecting corneal and conjunctival sensitivity measurement

PURPOSE

Measurement of sensitivity provides important clues about sensation on the ocular surface. This study aimed to evaluate whether measurements of threshold of sensation to an air stimulus are affected by corneal/conjunctival location, gender, age, time of day, ambient temperature or humidity.

METHODS

A retrospective analysis is reported of ocular surface threshold measurements made by one examiner using the CRCERT-Belmonte esthesiometer. Multiple corneal measurements for 49 normal subjects (24M:25F) and conjunctival measurements for 33 subjects (16M:17F) were included in the analysis. Threshold was measured at the corneal apex and at the inferior conjunctiva 2 mm from the limbus. Measurements were made between 9 AM and 6 PM, at ambient temperature 20 to 26 degrees C and humidity 52 to 87%. Mixed model analysis of variance, paired-t-test and Pearson's correlation were used to examine effects of various factors on threshold.

RESULTS

Mean group corneal threshold was 76.2+/-26.8 mL/min and conjunctival threshold 123.7+/-49.1 mL/min (n=33, p<0.001). Corneal and conjunctival threshold were well correlated (r=0.66, p<0.001). Thresholds were significantly higher for male than female subjects at both the cornea (M 82.2+/-23.5 mL/min, F 67.6+/-24.1 mL/min, p=0.04) and conjunctiva (M 144.1+/-40.7 mL/min, F 105.8+/-50.2 mL/min, p=0.02). A significant reduction in corneal threshold with age was apparent for females (n=25, r= -0.49 p=0.01) but not males. A similar effect on conjunctival sensitivity was not shown. No effect of time of day, ambient humidity or temperature was found on threshold at either site.

CONCLUSIONS

Corneal and conjunctival sensitivity were found to be associated. Corneal and conjunctival sensitivity is higher in female subjects, who also show an age-related increase in corneal sensitivity. No change in sensitivity of either tissue is apparent within normal levels of ambient temperature or humidity or over the course of a working day.

New insights into the diagnosis and treatment of neurotrophic keratopathy

Abnormalities of the ocular surface can be acquired or inherited disorders of the central nervous system. Loss of neural stimulation from the sensory division of the trigeminal nerve or from the autonomic nervous system can have devastating consequences on corneal epithelial wound healing and the precorneal tear film, leading to decreased vision. The pathogenesis of neurotrophic keratopathy is reviewed, and treatment modalities are recommended.

Contact Lens Care Products Effect on Corneal Sensitivity and Patient Comfort

PURPOSE

To evaluate the possible effect of two leading soft contact lens care products on corneal sensitivity, relative comfort, and superficial corneal staining in adapted disposable soft contact lens wearers.

METHODS

Eight disposable soft contact lens wearers equally divided between habitual users of OPTI-FREE Express Lasting Comfort No Rub formula (Alcon Laboratories, Fort Worth, TX) and ReNu MultiPlus (Bausch & Lomb, Rochester, NY) were enrolled in this crossover study. The habitual lens care product was designated the first crossover period. Patients completed a visual analog scale rating of midday and end-of-day comfort, underwent slitlamp examination for staining, and had corneal sensitivity measured by Cochet-Bonnet esthesiometry before and after being switched to the alternative lens care product. The lens care product used was masked from the investigator.

RESULTS

Patients habitually using OPTI-FREE Express reported higher comfort ratings than did patients using ReNu MultiPlus. On crossover, patients who initially used ReNu MultiPlus experienced similar comfort when using OPTI-FREE Express, but OPTI-FREE Express users experienced a substantial decrease in comfort when switched to ReNu MultiPlus. Esthesiometry showed significant differences in average sensitivity in favor of OPTI-FREE Express (P=0.0041). Statistical trends supported observed increases in corneal sensitivity when switching to OPTI-FREE Express and decreased corneal sensitivity when switching to ReNu MultiPlus. ReNu MultiPlus was also associated with slightly more corneal staining.

CONCLUSIONS

ReNu MultiPlus, a biguanide-based contact lens care product, was associated with decreased comfort during midday and end-of-day periods. ReNu MultiPlus was also associated with significant reduction in relative corneal sensitivity compared to Polyquad-based OPTI-FREE Express. Disturbance to normal corneal sensitivity may play a role in contact lens-related dry eye and discomfort. Further investigation is warranted.

Corneal mechanical sensitivity measurement using a staircase technique

PURPOSE

To determine the repeatability of an unequal staircase technique (Garcia-Perez Staircase, GPS) to measure corneal mechanical threshold using the CRCERT-belmonte Aesthesiometer, and to compare this with a previously-reported psychophysical method (method of constant stimuli, MOCS).

METHODS

The GPS, utilising unequal ascending and descending steps, was used to obtain a threshold measurement from the mean of six response reversals. repeatability was determined for the GPS and MOCS methods (N = 14), and threshold results obtained with each method were compared (N = 10).

RESULTS

The GPS (65.0 +/- 16.9 mL min(-1); CoR +/- 18.3 mL min(-1)) method was more repeatable than the MOCS (64.0 +/- 15.7 mL min(-1); CoR +/- 37.3 mL min(-1)) and the absolute values obtained with the two methods were not significantly different.

CONCLUSIONS

Although each method gave equivalent threshold results, the GPS method was more repeatable and quicker to apply and hence should reduce the influence of patient fatigue and help to minimise possible carry-over effects.

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.

The effect of long-term, daily contact lens wear on corneal sensitivity

PURPOSE

To assess the effect of long-term, daily-wear soft contact lenses and rigid gas permeable (RGP) contact lenses on corneal sensitivity using a noninvasive, air-pulse stimulus.

METHODS

The central and peripheral (temporal, medial, inferior) corneal sensation thresholds of 40 non-lens wearers, 40 soft lens wearers, and 40 RGP lens wearers were assessed using the Non-Contact Corneal Aesthesiometer (NCCA). The individuals who wore contact lenses were grouped according to the number of years of lens wear (10 years or less, 11-20 years, and 21 years or more).

RESULTS

Although a significant reduction in corneal sensitivity was found between the contact lens wearers and non-lens wearers (p = 0.000), no difference was found between the two lens-type subgroups (p = 0.939). This pattern of significance was repeated at each of the peripheral test locations. No relationship between corneal sensitivity and years of lens wear was found centrally (r2 = 0.004) or at any of the peripheral test locations. No significant difference was found between the central corneal sensation thresholds for the different subgroups of lens wear duration (p = 0.469) or for any of the peripheral test locations.

CONCLUSIONS

Both soft and RGP lens wear produce a similar type of corneal sensitivity loss, although the mechanism for this loss is different for the two lens types. The extent of sensitivity loss is not related to the duration of lens wear and appears to plateau after the first few months of wear. No topographical variation in sensitivity loss was found with lens type or with the duration of lens wear.

Effect of beam variables on corneal sensitivity after excimer laser photorefractive keratectomy

AIM

To investigate changes in corneal touch sensitivity following excimer laser photorefractive keratectomy (PRK) using different beam configurations.

METHODS

20 subjects were given a unilateral -3.00 D correction with either a 5 mm (26 micrograms, n = 10) or 6 mm (42 micrograms, n = 10) beam diameter. Thirty subjects underwent a unilateral -6.00 D correction with 5 mm (62 micrograms, n = 10), 6 mm (78 micrograms, n = 10), or multizone (62 micrograms, n = 10) treatments. The multizone treatment was 6 mm in diameter with the depth of the 5 mm treatment. Corneal sensitivity was measured using a slit-lamp mounted Cochet-Bonnet aesthesiometer before and at 1, 3, 6, and 12 months after PRK. Stimulus locations included points lying within the ablated zone (central) and outside (peripheral). These were compared with the equivalent locations in control (untreated) eyes.

RESULTS

There was a significant reduction in corneal sensitivity within the central (ablated) zone in all treatment groups after PRK. In most groups a return to full sensitivity was achieved by 6 months with the exception of the multizone treatment group which showed significant corneal hypoaesthesia at 12 months. Peripheral corneal sensitivity was also reduced in this group up to 3 months after the procedure. A comparison between the -3.00 D and -6.00 D treatment groups showed no significant difference. However, combining data from all treatment groups, a significant correlation was found between the interocular difference in central corneal sensitivity and postoperative haze at 3 and 6 months.

CONCLUSIONS

For corrections up to -6.00 D ablation depth and treatment zone diameter do not appear to be clinically important determinants of corneal hypoaesthesia. In contrast, postoperative corneal haze appears to correlate with sensitivity loss.