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. METHODS: A computerised Belmonte pneumatic esthesiometer was used to determine detection thresholds (using ascending method of limits), and to 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. For each suprathreshold stimulus, accommodative and pupil responses were measured with a validated eccentric infrared photorefractor. Quantitative differences in accommodative/pupil response, stimulus modality/intensity and left/right eye were analysed using repeated measures ANOVA. Tukey HSD tests were used for all post hoc analyses. RESULTS: Accommodation increased from baseline as the corneal apical stimulus intensity increased. This happened regardless of whether mechanical or chemical stimulation occurred (ANOVA, p < 0.05). At 200% threshold, accommodative response was greater than all stimulus intensities (Tukey HSD, all p < 0.05). There was no difference in pupil response between the stimulation intensities (100%, 150% and 200% threshold). There was no difference in accommodative response between the left and right eye for mechanical (ANOVA, p > 0.05) and chemical stimulation (ANOVA, p > 0.05). CONCLUSION: Noxious stimulation of the cornea seems to produce a dose-dependent increase in the accommodative response in the eyes but not a dose-dependent pupil response.

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 23°C and 35°C in their exposed (darkening) state at time points 0 s, 45 s, 90 s, and 15 min. and their unexposed (fading) state at 45 s, 15 min. and 20 min.. Mixed between and within repeated measures ANOVA (MRM-ANOVAs) and generalized additive modeling (GAMs) were used to compare the effects of temperature and solar exposure time on spectral transmittance of photochromic contact lenses. RESULTS: The mean (±SD) transmission of photochromic contact lenses in the exposed state were 94.7 ± 0.2, 39.1 ± 1.4, 27.0 ± 0.7 and 14.7 ± 1.0, and 93.7 ± 0.9, 38.8 ± 2.4, 30.2 ± 1.8, and 26.1 ± 1.0 at times 0 s, 45 s, 90 s, and 15 min. at 23°C and 35°C respectively. The mean (±SD) transmission of photochromic contact lenses in the unexposed state were 18.3 ± 1.5, 71.3 ± 2.4, and 80.2 ± 2.4, and 39.1 ± 1.0, 90.6 ± 1.0 and 91.1 ± 0.9 at times 45 s, 15 min. and 20 min. at 23°C and 35°C respectively. There was a significant decrease in light transmission as solar exposure time increased (GAM, MRM-ANOVA, p < 0.05). There was a significant effect of temperature and solar exposure time on the photochromic contact lenses (GAM, MRM-ANOVA, p < 0.05). The differences in the light transmitted by the photochromic contact lenses occurred at time 90 s and 15 min (Tukey HSD, at 90 s and 15 min, p < 0.05), where contact lenses at a temperature of 35°C showed greater light transmission than that at 23°C. There were differences in spectral transmittance based on the temperature of the contact lens. Contact lenses at 35°C transmitted more light than at 23°C at all unexposed times (MRM-ANOVA, p < 0.05). CONCLUSION: Spectral transmission of photochromic contact lenses were successfully measured with the ICS photochromic bench. Temperature appears to influence both the activation and deactivation of photochromic contact lenses such that the higher the temperature, the greater the light transmission.

Contact lens complications among wearers in Ghana.

PURPOSE: Contact lens (CL) practice is relatively new in Ghana; a country where the geographical location (warm climate) lends itself to harsh environmental conditions (high humidity) known to influence CL wear. Recent studies suggest an increase in CL wear (corrective and cosmetic), yet, there are no studies about CL-related complications. This study sought to determine the complications associated with CL wear in Ghana. METHODS: This was a retrospective cohort study. The medical records of contact lens wearers from five CL clinics in the two largest metropolises in Ghana, Accra and Kumasi, were reviewed. Included in the study were records of individuals who visited the clinics within the period of 2013-2016. Data on patients with contact lens-related complications were analyzed. RESULTS: The prevalence of CL complications was 29.06 %. The mean ±â€¯SD age of patients with CL complications was 35 ±â€¯15 years. Contact lens complications were more common in females (52.90 %). The majority of complications were in soft contact lens wearers (82.35 %). Refractive error correction was the most common indication for CL wear (61.76 %) among those with complications, followed by keratoconus (14.71 %), scarred blind eye (14.71 %), corneal ulcer (5.88 %) and anterior staphyloma (2.94 %). Contact lens complications reported were giant papillary conjunctivitis (41.18 %), corneal infiltrates (23.53 %), bacterial keratitis (14.71 %), corneal abrasion (11.76 %), dry eye (5.88 %) and corneal oedema (2.94 %). The causes of CL complication were inappropriate lens cleaning (29.41 %), poor hygiene (23.53 %), overnight contact lens wear (17.64 %), poor lens fit (14.71 %) and reaction to contact lens solution (14.71 %). CONCLUSION: Contact lens complications were more common in soft contact lens wearers in Ghana. Giant papillary conjunctivitis was the most common contact lens complication reported. Adherence to CL wear care regimen and good personal hygiene may prevent the majority of CL complications observed in Ghana.

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. For each stimulus, imaging of the stimulated/unstimulated eye was performed using two modified/calibrated Logitech c920 digital cameras for 4 seconds each, pre/post stimulus capture. The data were processed with a custom segmentation algorithm to help identify the pupils and pupil diameter was measured using ImageJ software. Pupil dilation response differences between the ipsi- and contralateral eye was analyzed using dependent t-tests. The effect of stimulus intensity, modality and sex of subjects were analyzed using repeated measures. RESULTS: In mechanical and chemical stimulation experiments, there was no difference in pupil responses between the stimulated eye and the unstimulated eye, (all dependent T-test p > 0.05). On average, pupil diameter increased from baseline as the corneal stimulus intensity increased. This happened regardless of whether mechanical or chemical stimulation occurred (ANOVA p < 0.05). At 200% threshold, pupil diameter was greater than at all stimulus intensities (Tukey HSD, all p < 0.05). Based on stimulus intensity, females had greater pupil diameters than males at levels of 150% threshold and 200% threshold (ANOVA p < 0.05, all Tukey HSD p < 0.05). CONCLUSION: This study serves as a basis for the characterization of the local stimulus-response neural circuitry relating nociceptive stimuli to autonomic responses and in combination with our work on completely separate autonomic circuits of bulbar conjunctival vessel dilation and reflex tearing suggests that the monotonic measurements of redness, tearing and pupils provide accurate, separable responses that reflect painful stimulus intensity.

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. METHODS: A computerized Belmonte pneumatic esthesiometer was used to determine detection thresholds (using ascending method of limits) and to 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. For each suprathreshold stimulus, a spectrophotometer was used to measure ipsilateral and contralateral conjunctival redness before and after delivery of the corneal stimulus. Redness between the stimulated and unstimulated eyes was analyzed using dependent t tests. The effects of stimulus intensity and modality on conjunctival redness were analyzed using repeated-measures analysis of variance (ANOVA). Tukey honestly significant difference tests were used for all post hoc analyses. P ≤ .05 was considered statistically significant. RESULTS: In mechanical and chemical stimulation experiments, the stimulated eye became redder than the unstimulated eye (all t tests, P > .05). On average, redness increased from baseline as the corneal stimulus intensity increased with corneal stimulation (ANOVA, P < .05). Chemical stimulation produced greater conjunctival redness than did mechanical stimulation at all stimulation levels (ANOVA, P < .05; all Tukey honestly significant difference tests, P < .05). CONCLUSIONS: Stimulation of the central cornea by noxious mechanical and chemical stimuli evokes a dose-dependent autonomic conjunctival redness response. Chemical stimulation of the cornea seems to evoke a greater response compared with mechanical stimulation. This study serves as a basis for the characterization of the local stimulus-response neural circuitry relating nociceptive ocular surface stimuli to autonomic responses.

Relationship between vessel diameter and depth measurements within the limbus using ultra-high resolution optical coherence tomography.

PURPOSE: To establish a relationship between the diameter and depth position of vessels in the superior and inferior corneo-scleral limbus using ultra-high resolution optical coherence tomography (UHR-OCT). METHODS: Volumetric OCT images of the superior and inferior limbus were acquired from 14 healthy subjects with a research-grade UHR-OCT system. Differences in vessel diameter and depth between superior and inferior limbus were analyzed using repeated measured ANOVA in SPSS and R. RESULTS: The mean (± SD) superior and inferior diameters were 29±18µm and 24±18µm respectively, and the mean (± SD) superior and inferior depths were 177±109µm and 207±132µm respectively. The superior limbal vessels were larger than the inferior ones (RM-ANOVA, p=0.004), and the inferior limbal vessels were deeper than the superior vessels (RM-ANOVA, p=0.041). There was a positive linear association between limbal vessel depth and size within the superior and inferior limbus with Pearson correlation coefficients of 0.803 and 0.754, respectively. CONCLUSION: This study demonstrated that the UHR-OCT was capable of imaging morphometric characteristics such as the size and depth of vessels in the limbus. The results of this study suggest a difference in the size and depth of vessels across different positions of the limbus, which may be indicative of adaptations to chronic hypoxia caused by the covering of the superior limbus by the upper eyelid. UHR-OCT may be a useful tool to evaluate the effect of contact lenses on the microvascular properties within the limbus.