Relationship between Corneal Sensation, Blinking, and Tear Film Quality

Age-Related Changes in Corneal Sensitivity

PURPOSE

The aim of this prospective cross-sectional cohort study was to clinically test whether corneal sensation decreases with age, based on subject feedback (psychophysical method), and whether it correlates with general pain perception.

METHODS

Subjects were recruited from 2 equally large age groups: group A (18-30 years) and group B (50-70 years; n = 45 per group). The inclusion criteria were healthy eyes, Ocular Surface Disease Index ≤13, and no contact lens wear. Corneal sensitivity threshold (CST) measurements were performed twice during each of the 2 visits, with the aid of the new Swiss liquid jet esthesiometer for corneal sensitivity (SLACS) and Cochet-Bonnet (CB) esthesiometer. A general pain sensitivity score was obtained from all participants.

RESULTS

Ninety subjects completed the study (n = 45 per age group, average age in group A: 24.2 ± 2.94 years, group B: 58.5 ± 5.71 years). Statistically higher CSTs for age group B were only observed for SLACS (mean difference: 1.58 dB, P < 0.001). No correlation was observed between the pain score and the CSTs obtained with either esthesiometry method (r = 0.11, P = 0.25 for liquid jet and r=-0.076, P = 0.61 CB).

CONCLUSIONS

A statistically significant decrease in corneal sensitivity was observed for the older age group with SLACS in this study, with CB however only a trend in the same direction was noted. General pain perception was not found to correlate with ocular surface sensation.

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.

Differential characteristics among asymptomatic and symptomatic meibomian gland dysfunction and those with dry eye

PURPOSE

To identify the characteristics of asymptomatic meibomian gland dysfunction (MGD), symptomatic MGD, and MGD coexisting with dry eye disease (DED).

METHODS

This cross sectional study enrolled a total of 153 eyes of 87 MGD patients. Participants filled in ocular surface disease index (OSDI) questionnaires. Age, gender, Schirmer's test, meibomian gland (MG) related parameters, lipid layer thickness (LLT) and blinking were compared among patients with asymptomatic MGD, symptomatic MGD, and MGD with DED. Multivariate regression was used to analyze the significant factor of DED in MGD. Spearman's rank correlation analysis was used to evaluate the association between the significant factors and MG function.

RESULTS

There was no difference in age, Schirmer's test, lid changes, MG secretion, and MG morphology among three groups. The OSDI of asymptomatic MGD, symptomatic MGD and MGD coexisting with DED were 8.5 ± 2.9, 28.5 ± 12.8 and 27.9 ± 10.5, respectively. Patients with MGD coexisting with DED exhibited more frequent eye blinking than that of patients with asymptomatic MGD (8.1 ± 4.1 vs. 6.1 ± 3.5 blinks/20 sec, P = 0.022), and reduced LLT than that of patients with asymptomatic MGD (68.6 ± 17.2 vs. 77.6 ± 14.5 nm, P = 0.010) and symptomatic MGD (78.0 ± 17.1 nm, P = 0.015). Multivariate analysis identified LLT (per nm, OR = 0.96, 95% CI = 0.93-0.99, P = 0.002) as a significant factor associated with DED development in MGD. The number of expressible MG was positively correlated with LLT (Spearman's correlation coefficient = 0.299, P = 0.016) but negatively correlated with the number of blinking (Spearman's correlation coefficient = -0.298, P = 0.016) in MGD patients with DED, and these findings were not identified in those without DED.

CONCLUSIONS

Asymptomatic MGD, symptomatic MGD, and MGD coexisting with DED share similar characteristics, including meibum secretion and morphology, but MGD patients coexisting with DED exhibited significantly reduced LLT.

The distribution of blinkrate among Malawian young adults: a cross-sectional study

Blink rate is a critical sign for numerous systemic and ocular conditions in medicine, however, the literature reports varying values for the parameter. Hence, the aim of this study was to establish the cut-off blink rate value among Malawian young adults including the effects of sex and age on the parameter. This was a quantitative descriptive cross-sectional study conducted among students at Mzuzu University in Malawi. The study recruited 98 participants, 50% male and 50% female. The age ranged from 17-45 years. The blink rate was measured manually by observing the number of blinks per minute. The average blink rate was 16.04 (SD = 6.417) blinks per minute. The Blink rate was not significantly correlated with age (P = 0.066) and sex (P = 0.8143). Our study confirms that blink rate varies according to geographical location as a factor of different weather conditions. Moreover, we found no age and sex-related differences in blink rate.

Effects of cataract surgery on blinking

PURPOSE

To assess the effects of cataract surgery on the spontaneous blinking pattern and blinking kinematics.

SETTING

FISABIO Oftalmología Médica Eye Hospital, Valencia, Spain.

DESIGN

Observational descriptive clinical study.

METHOD

Patients with senile cataract were evaluated before (visit 1) and at 1 month (visit 2) and 3 months (visit 3) after undergoing phacoemulsification cataract surgery. The blinking of patients was recorded for 90 seconds using an eye-tracking device. Blinks were analyzed by means of image analysis to obtain a noninvasive detailed description of blinking including blink rate, number of complete and incomplete blinks, percentage of incomplete blinks, and kinematic parameters, including amplitude, closing, contact, opening, and total durations and closing and opening speeds.

RESULTS

50 patients were included in this study. The blink rate was significantly smaller at visit 3 compared with baseline ( P = .03) and visit 2 ( P = .001). Likewise, the number of complete blinks was significantly smaller, and the percentage of incomplete blinks was significantly higher at 3 months postoperatively compared with baseline ( P = .02 and P = .01, respectively), although no differences were observed at 1 month postoperatively ( P > .05). Conversely, no differences in the number of incomplete blinks or any kinematic parameter were observed between visits ( P = .12).

CONCLUSIONS

Cataract surgery significantly altered the blinking pattern at 3 months postoperatively, although kinematic parameters remained unvaried. Clinicians should be aware of potential alterations in blinking after phacoemulsification cataract surgery and the implications this may have on the ocular surface of patients.

Ocular Surface Temperature in DED under Natural Non-Controlled Blinking Conditions

Infrared (IR) thermography is a tool to non-invasively assess the tear film temperature. The aim was to analyze ocular surface temperature (OST) variations in dry eye disease (DED) and control eyes under natural non-controlled blinking conditions. Imaging was performed with a thermal camera (FLIR Systems Inc.) at 30 Hz framerate in 79 participants (39 DED (62.5% women, average age 48 ± 20 years) and 40 control (46.2 % women, average age 38 ± 13 years)) using non-contact IR thermography camera. Data acquisitions were performed in natural blinking conditions for 40 s. IR images were analyzed using a custom algorithm that calculates the OST indexes: mean OST, OST at the start and at the end, minimum and maximum OST, and tear evaporation rate (TER). No significant differences were found between groups in any thermal parameter analyzed (paired comparisons t-test, p > 0.05). In conclusion, the findings of this study did not reveal significant differences between DED and control eyes under natural non-controlled blinking conditions. However, the presence of clinical signs in the control group may affect the results, highlighting the role of DED diagnosis criteria.

Working principle and relevant physical properties of the Swiss Liquid Jet Aesthesiometer for Corneal Sensitivity (SLACS) evaluation

Purpose

To describe and evaluate relevant physical properties of the Swiss Liquid Jet Aesthesiometer for Corneal Sensitivity (SLACS) for ocular surface sensitivity measurement.

Methods

Characteristics of Liquid Jet (LJ) droplets (consisting of isotonic saline solution) were analysed: vertical and horizontal displacement and speed of LJ droplets were recorded with the aid of the High Speed Photron FASTCAM NOVA S6 camera (stimulus duration: 40 ms). Stimulus mass was assessed for 20 sets of 10 LJs with aid of a microbalance (pressure range of 100–1500 mbar).

Results

Because continuous flow LJ disintegrated into droplets in the lower pressure range (<700 mbar), pulsed stimuli were applied in order to obtain similar stimulus characteristics across the applied pressure range. For all measurements, very little variability was observed. Vertical and horizontal displacement did not exceed 0.13 mm in either direction. The mass per shot showed an unexpected cubic dependency on pressure. Up to approximately 700 mbar, LJ speed showed an almost linear relationship. For the pressure range of >700–1500 mbar, variability increased and speed decreased compared to the expected in a linear manner. However, this may be caused by the difficulty of identifying pattern changes of LJ droplets from one high speed image frame to the next with increasing stimulus speed, when determining LJ speed via pixel count.

Conclusions

Swiss Liquid Jet Aesthesiometer for Corneal Sensitivity was shown to deliver fine droplets with a pulsed stimulus mode, in a repeatable manner with precise localisation to the ocular surface. Very little variability was observed in LJ speed and mass for the typical pressure range required for clinical sensitivity measurements.

Ocular surface cooling rate associated with tear film characteristics and the maximum interblink period

The surface of the human eye is covered with a protective tear film that refreshes with each blink. Natural blinking occurs involuntarily, but one can also voluntarily blink or refrain from blinking. The maximum time one can refrain from blinking until the onset of discomfort is the maximum interblink period (MIBP). During the interblink period the tear film evaporates and thins from the ocular surface. Infrared thermography provides a non-invasive measure of the ocular surface temperature (OST). Due to evaporation, ocular surface cooling (OSC) generally occurs when the eyes are open and exposed to the environment. The purpose of our study was to investigate the effect of OSC rate on the MIBP, and to investigate the association of the MIBP with tear film characteristics in subjects who do and do not exhibit OSC. The MIBP was measured simultaneously with OST over time. Non-invasive tear breakup time, tear meniscus height, tear lipid layer thickness, and Schirmer I test strip wetted lengths were measured on a day prior to the thermography visit. Subjects were divided into cooling and non-cooling groups based on OSC rate, and demographic and tear film characteristics were tested for inter-group differences. A faster OSC rate was associated with an exponentially shorter duration of the MIBP overall and within the cooling group alone. Faster non-invasive tear breakup time was significantly associated with a shorter MIBP in both groups. These results suggest that tear film evaporation initiates a pathway that results in the onset of ocular discomfort and the stimulus to blinking. The presence of a subset of subjects with no or minimal OSC who nevertheless have a short MIBP indicates that evaporative cooling is not the only mechanism responsible for the onset of ocular discomfort.

Impact of virtual reality headset use on eye blinking and lipid layer thickness

PURPOSE

Blinking plays an important role in protecting the eyes, and the use of computers has been associated with a reduction in the blink rate. The goal of this study was to evaluate the effect of a virtual reality headset on blinking and lipid layer thickness and to compare these data to those associated with a conventional desktop monitor.

METHODS

Two experiments were performed to compare the effect of 20minutes of use of a virtual reality headset (FOVE) and 20minutes of use of a desktop monitor on the frequency and length of blinks (experiment 1, 15 participants) and on the thickness of the lipid layer as measured by Lipiview (experiment 2, 12 participants).

RESULTS

In the first experiment, the blink rate [F(1.83)=4.3, P=0.04, β=0.36] and duration [F(1.83)=13, P=0.001, β=0.35] increased with time under both conditions, but no statistical difference was found between the two conditions (headset vs. desktop monitor) either for blink rate [rmANOVA F(1.11)=0.01, P=0.92; headset: 15.1 blinks, 95% CI: 12.6 to 17.6 blinks; desktop: 14.6 blinks, 95% CI: 13.6 to 15.7 blinks] or for blink duration [rmANOVA F(1.11)=4.534, P=0.06; headset: 205.75ms, 95% CI: 200.9 to 210.6ms; desktop: 202.82ms, 95% CI: 198.2 to 207.5ms]. However, strong individual variations were observed. Evaluation of simulator sickness and visual fatigue by questionnaire showed no significant differences between the two conditions (SSQ simulator sickness questionnaire: V=46, P=0.62; VFQ visual fatigue questionnaire: V=15.5, P=0.13). In the second experiment, the lipid layer thickness increased significantly after use of the VR headset [F(1.18)=11.03, P=0.004, headset: 76.2nm, desktop: 58.8nm].

CONCLUSION

In terms of recommendations, the effect of virtual reality headsets on blink duration and frequency during a moderate exposure (20minutes) is comparable to that of a conventional desktop monitor. However, the strong individual variations observed, the lack of reliable tests to evaluate this individual sensitivity, and the significant increase in lipid layer thickness in experiment 2 suggest the value of a more detailed investigation, in particular with consideration of a longer exposure time and other tear film parameters.

Macaque monkey trigeminal blink reflex circuits targeting orbicularis oculi motoneurons

The trigeminal blink reflex plays an important role in protecting the corneal surface from damage and preserving visual function in an unpredictable environment. The closing phase of the human reflex, produced by activation of the orbicularis oculi (ObOc) muscles, consists of an initial, small, ipsilateral R₁ component, followed by a larger, bilateral R₂ component. We investigated the circuitry that underlies this reflex in macaque (Macaca fascicularis and Macaca mulatta) monkeys by the use of single and dual tracer methods. Injection of retrograde tracer into the facial nucleus labeled neurons in the principal trigeminal nucleus, and in the spinal nucleus pars oralis and interpolaris, bilaterally, and in pars caudalis, ipsilaterally. Injection of anterograde tracer into the principal trigeminal nucleus labeled axons that directly terminated on ObOc motoneurons, with an ipsilateral predominance. Injection of anterograde tracer into pars caudalis of the spinal trigeminal nucleus labeled axons that directly terminated on ipsilateral ObOc motoneurons. The observed pattern of labeling indicates that the reticular formation ventromedial to the principal and spinal nuclei also contributes extensive bilateral input to ObOc motoneurons. Thus, much of the trigeminal sensory complex is in a position to supply a monosynaptic drive for lid closure, and the adjacent reticular formation can supply a disynaptic drive. These findings indicate that the assignment of the R₁ and R₂ components of the blink reflex to different parts of the trigeminal sensory complex cannot be exclusively based on subdivision connectional relationships with facial motoneurons. The characteristics of the R₂ component may be due, instead, to other circuit properties.

Manual interferometric device for routine non-invasive tear film break-up time assessment

Purpose: To determine the feasibility of non-invasive tear break-up time (NIBUT) assessment using the Handheld tear lipid layer thickness assessment instrument and compare it with the standard tear break-up time (TBUT) test and other dry eye tests.Subjects and methods: 108 subjects were enrolled, 56 with and 52 without dry eye symptoms. Schein questionnaire was used to determine the severity of dry eye symptoms. Ocular signs were assessed by NIBUT, TBUT, lipid layer thickness (LLT), lid-parallel conjunctival folds (LIPCOF), conjunctival hyperemia, and corneal staining.Results: Median NIBUT and TBUT, and other clinical test values significantly differed among the dry eye symptoms group and control group. NIBUT yielded the most significant difference between the groups (NIBUT: 7 sec vs. 17.5 sec, p < .001, Z = 5.94; TBUT: 5 sec vs. 10 sec, p < .001, Z = 4.38; LLT: p = .007; LIPCOF: p < .001, conjunctival hyperemia: p < .047, corneal staining: p < .010). Spearman's test showed a significant correlation between NIBUT and TBUT (p < .001), NIBUT and LLT (p = .001), NIBUT and LIPCOF (p = .019), NIBUT and conjunctival hyperemia (p = .002), and NIBUT and corneal staining (p = .012) in the dry eye symptoms group. NIBUT did not significantly differ among the three measurements in both groups of patients (p = .061, p = .096), while TBUT values did in the control group (p < .001). Short NIBUT values were the main predictors and indicators of dry eye complaints (AOR = 0.87, p < .001), superior to TBUT (AOR = 0.88, p = .008) and other tests even after adjustment for age and gender.Conclusion: NIBUT measured by Handheld instrument is a simple, accessible, practical, and, most of all, reproducible and objective method that might allow NIBUT assessment on a regular basis.

Lipid conformational order and the etiology of cataract and dry eye

Lens and tear film lipids are as unique as the systems they reside in. The major lipid of the human lens is dihydrosphingomylein, found in quantity only in the lens. The lens contains a cholesterol to phospholipid molar ratio as high as 10:1, more than anywhere else in the body. Lens lipids contribute to maintaining lens clarity, and alterations in lens lipid composition due to age are likely to contribute to cataract. Lens lipid composition reflects adaptations to the unique characteristics of the lens: no turnover of lens lipids or proteins; the lowest amount of oxygen of any tissue; and contains almost no intracellular organelles. The tear film lipid layer (TFLL) is also unique. The TFLL is a thin (100 nm) layer of lipid on the surface of tears covering the cornea that contributes to tear film stability. The major lipids of the TFLL are wax esters and cholesterol esters that are not found in the lens. The hydrocarbon chains associated with the esters are longer than those found anywhere else in the body (as long as 32 carbons), and many are branched. Changes in the composition and structure of the 30,000 different moieties of TFLL contribute to the instability of tears. The focus of the current review is how spectroscopy has been used to elucidate the relationships between lipid composition, conformational order and function, and the etiology of cataract and dry eye.

EFFECT OF PANRETINAL PHOTOCOAGULATION ON CORNEAL SENSATION AND TEAR FUNCTION IN PATIENTS WITH DIABETIC RETINOPATHY

PURPOSE

To evaluate the early effects of panretinal photocoagulation (PRP) on corneal sensation and dry eye signs in patients with diabetic retinopathy.

METHODS

Fifty patients with Type 2 diabetes mellitus and very severe nonproliferative or non-high-risk proliferative diabetic retinopathy who required PRP for the treatment of their retinal condition were enrolled. All patients were treated using a pattern PRP device. Esthesiometry, tear breakup time test, Schirmer test, and corneal staining pattern were evaluated at baseline and 2 months after the last session of PRP.

RESULTS

Data from 88 eyes of 50 patients (41 right eyes and 47 left eyes) were analyzed. The mean tear breakup time test (right eyes) was decreased from 9.51 at baseline to 7.66 seconds after PRP (P < 0.001). The post-PRP eyes showed more advanced grades of corneal staining than pre-PRP assessment (P < 0.001). The average value of Schirmer test was 14.39 versus 12.29 mm (without anesthesia; P < 0.001) and 8.17 versus 7.15 mm (with anesthesia, P < 0.001) for baseline versus post-PRP measurements, respectively. The corneal sensation also showed decrease after laser therapy (4.93 versus 4.31 cm; P < 0.001).

CONCLUSION

This study demonstrates that decreased corneal sensation and signs of dry eye are more common immediately after PRP for diabetic retinopathy. These conditions should be discussed with the patient preoperatively and managed postoperatively.

Objective and subjective evaluation of tear film in machine carpet weavers

OBJECTIVES

The present study was conducted to evaluate the status of tear film objectively and subjectively in machine carpet weavers.

METHODS

In this cross-sectional study, machine-made carpet weavers were compared with the controls who were selected from people working in other parts of the factory except for the production. A complete evaluation of ocular health was done for all participants. The blink rate, tear deformation Time (TDT), and ocular staining were evaluated as an objective assessment and the ocular surface disease index (OSDI) was used for a subjective assessment of the tear film status. The results were compared between the two groups using the SPSS software.

RESULTS

The results of 46 weavers (mean age: 38.43 ± 6.10 years) and 46 controls (mean age: 33.20 ± 8.40 years) were analyzed. The mean of blink rate and OSDI score were significantly higher in weavers (Blink rate: 20.67 ± 4.18 blink/min, OSDI: 22.59 ± 9.51) in comparison with controls (Blink rate: 14.00 ± 3.30 blink/min, OSDI: 6.22 ± 4.78, P < .001). The mean TDT value of the weavers was significantly lower compared with the controls (10.27 ± 3.01 and 16.58 ± 4.18 s respectively, P < .001). Ocular surface staining was seen among 60.9% of weavers while there was 6.5% in the controls (P < .001). Based on the TDT test and OSDI results together, the percentage of dry eye in the weavers was 43.5% and that in the non-weavers was 2.2%, which showed that the relationship between weaving and dry eyes was statistically significant (P < .001).

CONCLUSIONS

The results indicate that increased symptoms and decreased tear stability in weavers compared with non-weavers lead to more tear film abnormalities in these individuals.

Clinical efficacy of eyelid hygiene in blepharitis and meibomian gland dysfunction after cataract surgery: a randomized controlled pilot trial

The purpose of this randomized clinical trial is to evaluate the effect of eyelid hygiene on subjective symptoms, anterior blepharitis, and meibomian gland dysfunction (MGD) after cataract surgery. Subjects with obstructive MGD who underwent cataract surgery were randomly divided into two groups. In the eyelid hygiene group, eyelid hygiene was performed twice a day for 10 days from 3 days before to 1 week after cataract surgery. The control group did not perform eyelid hygiene. A subjective symptom questionnaire of SPEED, anterior blepharitis grade, and meibum quality and quantity was evaluated at baseline and at postoperative 1 and 4 weeks. The eyelid hygiene group (n = 36) showed decreased SPEED score after cataract surgery and the control group (n = 33) did not. Anterior blepharitis grade was worse 1 week after surgery in the control group but not in the eyelid hygiene group. The control group had significantly decreased meibum quality and quantity in both the upper and lower eyelids after cataract surgery, but the eyelid hygiene group did not. Eyelid hygiene before/after cataract surgery improved postoperative subjective symptoms and prevented postoperative exacerbation of anterior blepharitis and MGD. Thus, perioperative eyelid hygiene is recommended for patients with obstructive MGD who undergo cataract surgery.

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

Purpose

To determine the feasibility of using a portable carbon dioxide (CO₂) 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 CO₂ (%CO₂). These stimuli were calibrated using a portable CO₂ sensor (COZIR CM-0041) and data logger, delivered for 100 seconds by using the Waterloo Belmonte esthesiometer. The distances between the sensor and esthesiometer tip were 0 (to measure feasibility), 3, 5, and 10 mm. In experiment I, 100% CO₂ was tested using four different flow rates (50, 100, 150, and 200 mL/min) at three working distances. In experiment II, flow rates of 20 to 100 mL/min and concentrations of 20% to 100% CO₂ were tested in 20 steps at 3 working distances.

Results

The CO₂ sensor correctly reported the esthesiometer extremes of 0% and 100% CO₂ when placed at the esthesiometer tip. There were progressive, systematic increases in concentrations reaching/reported by the sensor with increasing flow rates and nominal concentrations and progressive decreases in measurements with increases in working distance.

Conclusions

CO₂ concentrations in pneumatic esthesiometers can be calibrated and, as expected, vary with flow rate and distance, highlighting the importance of calibration and standardization of CO₂ stimuli in these instruments.

Translational Relevance

Calibrated CO₂, a chemical sensory stimulus in humans, may be used in testing the surface of the eye as well as other membranes within which the CO₂ can be dissolved (e.g., mucous) to produce an acidic stimulus.

Association among Blink Rate, Changes in Ocular Surface Temperature, Tear Film Stability, and Functional Visual Acuity in Patients after Cataract Surgery

Purpose

To investigate the association among the ocular surface temperature (OST), tear film stability, functional visual acuity (FVA), and blink rate in patients after cataract surgery.

Methods

We recruited 98 eyes of 69 patients (mean age, 73.7 ± 5.2 years) 1 month after phacoemulsification with implantation of acrylic intraocular lenses and assessed slit-lamp microscopy, corrected distance VA, FVA, noninvasive tear breakup time (NIBUT), and OST. We defined the changes in the OST from 0 to 10 seconds after eye opening as the ΔOST. We measured the FVA and blink rate using the FVA measurement system. We divided the patients into two groups based on tear film stability: stable tear film (NIBUT, >5.0 seconds) and unstable tear film (NIBUT, ≤5.0 seconds). We evaluated the differences between the two groups and the association between the blink rate and other clinical parameters.

Results

The unstable tear film group (56 eyes) had significantly (p < 0.0001, unpaired t-test) shorter NIBUTs than the stable tear film group (42 eyes). The ΔOSTs and blink rates were significantly (p < 0.0001) higher in the unstable tear film group than in the stable group. Linear single regression analysis showed that the ΔOST (r = −0.430, p < 0.0001), NIBUT (r = −0.392, p < 0.0001), and gender (r = −0.370, p=0.0002) were correlated significantly with the blink rate. Multiple regression analysis showed that the ΔOST independently contributed to the blink rate.

Conclusions

The frequency of blinks is associated with tear film stability in patients after cataract surgery. The blink rate may be useful for evaluating the tear film stability in clinical practice. The ΔOST should be an important contributing factor to the blink rate. [This trial is registered with UMIN000026970].

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.

Ambient Air Currents Activate Corneal Nerves During Ocular Desiccation in Rats: Simultaneous Recordings of Neural Activity and Corneal Temperature

Purpose

Previously we found two types of corneal neurons that we hypothesized to play an important role in tearing. One type is called low threshold–cold sensitive plus dry sensitive (LT-CS + DS), and the other is termed high threshold–cold sensitive plus dry sensitive (HT-CS + DS). The present study examined critical stimuli influencing the activity of these neurons to elucidate environmental factors that may trigger this ocular reflex.

Methods

Single corneal neurons were extracellularly recorded from the trigeminal ganglia in response to ocular stimuli that mimic environmental conditions one encounters in daily life. They included an ocular desiccation and slight air currents and were presented while simultaneously monitoring the ocular surface temperatures (OST) in rats.

Results

The results showed that the changes in steady state (SS) activity of the neurons closely followed the changes in SS OST: during the sustained ocular desiccation, neural firing displayed numerous small sudden increases in activities (“spiking”); these “spiking” activities of LT-CS + DS neurons were replicated by a minute air current that induced slight ocular surface cooling of approximately 0.2–0.1°C; and the responses of HT-CS + DS neurons showed an inconsistent relationship to the changes in SS OST or exhibited little evidence for “spiking” activities.

Conclusions

These results suggest that LT-CS + DS neurons play a role in the afferent trigger of tearing as we face the environment, exposing the cornea to prevailing air currents that produce a slight cooling of the ocular surface. By contrast, HT-CS + DS neurons may serve to protect the eyes from extreme dryness by eliciting nociception-evoked tearing when the OST or osmolarity of tears becomes injurious.

NONINVASIVE TEAR FILM BREAK-UP TIME ASSESSMENT USING HANDHELD LIPID LAYER EXAMINATION INSTRUMENT

The aim was to determine feasibility and reliability of noninvasive tear break-up time (NIBUT) assessment using handheld lipid layer examination instrument, and to compare it with standard tear break-up time (TBUT) test. Fifty patients were enrolled, 31 with and 19 without dry eye symptoms. Schein questionnaire was used to assess dry eye symptoms. During examination, three NIBUT measurements were performed on each eye using handheld instrument, followed by three TBUT measurements. Receiver operating characteristic curves, sensitivity, specificity and logistic regression analysis were generated. Median NIBUT values were significantly shorter in dry eye symptom group than in control group in all three measurements (9, 8 and 8 s vs. 21, 22 and 21 s; p<0.001). TBUT values showed no significant difference between the groups in the first measurement (p=0.053), but the values were significantly shorter in dry eye symptom group in second and third measurements (p=0.020). The cutoff value to distinguish patients with symptoms of dry eye from control group was 12 seconds for NIBUT and 8 seconds for TBUT, with NIBUT having significantly higher sensitivity, specificity, area under the receiver operating characteristic curve and positive predictive value. NIBUT, measured by handheld lipid layer examination instrument, was superior to TBUT in detecting dry eye.

Pre-contact lens and pre-corneal tear film kinetics

PURPOSE

Contact lenses (CL) insulate the corneal surface from the environment. It is possible that they influence the corneal sensory mechanism that contribute to spontaneous blinking. The study objective was to quantify the pre-CL and pre-corneal tear film kinetics (TFK) over blink period.

METHODS

The study population was 202 soft CL wearers, 133 non-lens wearers. TFK were quantified via post-hoc masked analysis of HD Tearscope videos. The parameters were: Non-Invasive Break Up Time (NIBUT), Exposed Area % at initial break (EA 1st Break) and at blink (EA Blink), Interblink period (IB), Protective Index (PI) and exposure speed of surface dehydration (ES mm2/s). The TFK of CL wearers were compared to non-lens wearers. The hypothesis was that pre-CL TFK was inferior to pre-corneal, specifically greater tear film anomalies presence at blink.

RESULTS

The pre-corneal NIBUT was longer than pre-CL NIBUT (9.1 vs. 5.1s, p < 0.001). The EA 1st Break was smaller for pre-corneal than pre-CL (0.003 vs. 0.43%, p < 0.001). The mean IB time was similar for pre-CL and pre-corneal (9.4 vs. 9.8s, p = 0.213). The EA Blink % was smaller for pre-corneal than pre-CL (0.03 vs. 6.66%, p < 0.001). The ES was faster for pre-CL than pre-corneal (0.339 vs. 0.004, p < 0.001). The PI was greater for pre-corneal than pre-CL (99.9 vs. 97.1%, p < 0.001).

CONCLUSIONS

Pre-CL TFK were significantly inferior than pre-corneal, confirmed the hypothesis. The NIBUT was shorter. Once the initial break occurred, ES was faster, and EA was much greater for pre-CL than pre-corneal. The differences identified may be an aetiological component of CL discomfort and the relationship between TFK and discomfort in contact lens wearers should be investigated.

Relationships Between Meibomian Gland Loss and Age, Sex, and Dry Eye

PURPOSE

This study evaluated relationships between meibomian gland loss (MGL) and age, sex, and dry eye.

METHODS

Dry eye and MGL of the lower eyelid was evaluated from 112 randomly selected subjects (66 women; mean age 62.8; SD ±15.7; and age range: 19-89 years) from Horst Riede GmbH, Weinheim, Germany. In addition, subjects were grouped into dry eye and non-dry eye by the Ocular Surface Disease Index (OSDI) score, lid-parallel conjunctival folds and non-invasive break-up time. Symptoms were evaluated by the OSDI. Meibography of the lower eyelid was performed using a Cobra camera (bon Optic, Lübeck, Germany), and images were analyzed by its digital grading tool. Data were analyzed by backward, multiple regression analyses and Pearson correlation.

RESULTS

Analyzing all subjects, multiple regression analyses detected that age and dry eye status (dry eye diagnosis or OSDI) but not sex were significantly related to MGL. In both, non-dry eye (n=66) and dry eye subjects (n=46), dry eye status (OSDI) but not age or sex was significantly related to MGL. Ocular Surface Disease Index scores were significantly correlated with MGL, but this correlation was stronger among all subjects (Pearson correlation; r=0.536, P<0.001) and dry eye group subjects (r=0.520, P<0.001) than in non-dry eye group subjects (r=0.275, P=0.014).

CONCLUSIONS

Dry eye group subjects showed significantly increased MGL of the lower eyelid. Age and dry eye status were related to MGL of the lower eyelid, but sex was not; dry eye status was the dominant factor.

Blink Test enhances ability to screen for dry eye disease

AIM

To evaluate the patient-administered Optrex^™ Dry Eye Blink Test against established clinical criteria for the diagnosis of dry eye disease (DED) and to evaluate its benefit in enhancing screening for DED.

METHODS

Eighty-seven participants aged 38 ± 17 years, (44 female) were screened for DED using the Tear Film and Ocular Surface Society Dry Eye Workshop II (TFOS DEWS II) diagnostic criteria. In addition to symptoms screening with the Ocular Surface Disease Index questionnaire (≥13 cut-off score for DED), these criteria required a sign of loss of homeostasis of the tear film in the form of a non-invasive tear breakup time (NIBUT) <10 s (Oculus Keratograph; K5M), an osmolarity reading ≥308 mOsm/L or an interocular difference in osmolarity of >8 (Tearlab), or ocular surface staining (>5 fluorescein corneal spots, >9 lissamine green spots or lid wiper staining [≥2 mm length & ≥25% width]) to confirm a diagnosis of DED. The self-administered Blink Test, which requires the participant to observe an image on a computer screen and report the length of time (in seconds) that they can refrain from blinking without discomfort, was repeated three times.

RESULTS

Using a cut-off time of 10 s, the Blink Test demonstrated sensitivity of 66%, specificity of 88%, and an area under the curve of 0.77 (p < 0.001), in predicting a diagnosis of DED according to the TFOS DEWS II criteria. The correlation between the Blink Test and NIBUT was r = 0.47 (p < 0.001). When combined with the screening questionnaire, the sensitivity and specificity of the Blink Test increased to 71% and 90%, respectively.

CONCLUSION

The Blink Test offers health professionals without advanced instrumentation, as well as patients, themselves, a rapid method of identifying possible DED.

Acute hyperalgesia and delayed dry eye after corneal abrasion injury

Introduction:

Corneal nerves mediate pain from the ocular surface, lacrimation, and blinking, all of which protect corneal surface homeostasis and help preserve vision. Because pain, lacrimation and blinking are rarely assessed at the same time, it is not known whether these responses and their underlying mechanisms have similar temporal dynamics after acute corneal injury.

Methods:

We examined changes in corneal nerve density, evoked and spontaneous pain, and ocular homeostasis in Sprague-Dawley male rats after a superficial epithelial injury with heptanol. We also measured changes in calcitonin gene-related peptide (CGRP), which has been implicated in both pain and epithelial repair.

Results:

Hyperalgesia was seen 24 hours after abrasion injury, while basal tear production was normal. One week after abrasion injury, pain responses had returned to baseline levels and dry eye symptoms emerged. There was no correlation between epithelial nerve density and pain responses. Expression of both ATF3 (a nerve injury marker) and CGRP increased in trigeminal ganglia 24 hours after injury when hyperalgesia was seen, and returned to normal one week later when pain behavior was normal. These molecular changes were absent in the contralateral ganglion, despite reductions in corneal epithelial nerve density in the uninjured eye. By contrast, CGRP was upregulated in peripheral corneal endings 1 week after injury, when dry eye symptoms emerged.

Conclusion:

Our results demonstrate dynamic trafficking of CGRP within trigeminal sensory nerves following corneal injury, with elevations in the ganglion correlated with pain behaviors and elevations in peripheral endings correlated with dry eye symptoms.

Effects of Tear Film Lipid Layer Thickness and Blinking Pattern on Tear Film Instability After Corneal Refractive Surgery

PURPOSE

To investigate associations between changes in tear film instability and the lipid layer thickness (LLT) and blink pattern after corneal refractive surgery (CRS).

METHODS

Forty patients were enrolled in this study. The LLT and blink pattern were evaluated 1 week before and 30 days after CRS using a novel interferometer and an ocular surface disease index (OSDI) questionnaire, and other tear film stability markers were also evaluated.

RESULTS

Mean OSDI scores increased from 5.52 to 8.54 (P = 0.016), corneal fluorescence staining scores increased from 0.05 to 0.25 (P = 0.034), first noninvasive tear breakup time (NIBUT-F) decreased from 9.66 to 7.33 seconds (P = 0.014), and average noninvasive tear breakup time (NIBUT-Ave) decreased from 12.32 to 10.26 seconds (P = 0.047) 1 month after CRS. Meanwhile, mean total blink frequency in 20 seconds decreased significantly from 12.62 to 6.31 (P < 0.001); LLT did not change significantly (P = 0.447). The change in NIBUT-Ave was positively correlated with that in LLT (P = 0.003) and negatively correlated with that in the partial blink rate (P = 0.013). The changes in the OSDI questionnaire, NIBUT, LLT, and blink pattern were not different between the laser-assisted in situ keratomileusis and laser-assisted subepithelial keratomileusis groups.

CONCLUSIONS

A decrease in tear film stability occurs 1 month after CRS, the change in the blink pattern and unchanged LLT preoperatively and postoperatively suggesting that these parameters play a role in maintaining tear film stability after CRS.

Review of Literature on Measurements of Non-invasive Break Up Times, Lipid Morphology and Tear Meniscal Height Using Commercially Available Hand-held Instruments

Purpose/aims: Dry eye is a common multi-factorial disease characterized by tearfilm dysfunction. Diagnosis of dry eye requires documentation of tear status with non-invasive tear break up times (NIBUT), tear meniscal height (TMH), and tearfilm lipid layer. These parameters objectively assess tear stability and indirectly, the functional impact of meibomian gland dysfunction. While it is obvious that portable instrumentation gives broader access than fixed instrumentation, its value would be limited if it is unreliable and its precision and accuracy substantially worse than fixed instruments.

MATERIALS/METHODS

Because of the lack of systematic reviews concerning the Tearscope, we performed a scoping review of the literature to determine 1. the ranges of the tear parameters as measured by the device, 2. relationship between these measurements and other clinical variables, 3. Information about intra or inter-observer agreement, and comparison with another technique, where available.

RESULTS

We found 22 reports related to NIBUT, 18 reports concerning tearfilm lipid morphology (LM) based on classification of interference patterns, and 8 reports on TMH. While publication of these reports indicates an acceptance of the reliability of portable instruments, we interrogated these studies further to evaluate the results obtained from portable devices and found that there was no equivalent measurements in fixed devices (LM) or measurements differ considerably from fixed devices (NIBUT). In the case of TMH, portable measurements were similar to those by traditional slit-lamp microscopy. There were relatively few studies on TMH measured using handheld devices, but it was found to be correlated to NIBUT but not the Schirmer test values.

CONCLUSIONS

Imaging algorithms in portable tearfilm instruments should be further standardized to facilitate wider adoption and evaluation. In the next few years, new emerging technologies will employ a strategy of non-invasive tear testing that is portable and relatively inexpensive, and these will enhance adoption of such tools in the clinic.

Human Meibum Age, Lipid-Lipid Interactions and Lipid Saturation in Meibum from Infants

Tear stability decreases with increasing age and the same signs of instability are exacerbated with dry eye. Meibum lipid compositional changes with age provide insights into the biomolecules responsible for tear film instability. Meibum was collected from 69 normal donors ranging in age from 0.6 to 68 years of age. Infrared spectroscopy was used to measure meibum lipid phase transition parameters. Nuclear magnetic resonance spectroscopy was used to measure lipid saturation. Increasing human meibum lipid hydrocarbon chain unsaturation with age was related to a decrease in hydrocarbon chain order, cooperativity, and in the phase transition temperature. The change in these parameters was most dramatic between 1 and 20 years of age. Meibum was catalytically saturated to determine the effect of saturation on meibum lipid phase transition parameters. Hydrocarbon chain saturation was directly related to lipid order, phase transition temperature, cooperativity, changes in enthalpy and entropy, and could account for the changes in the lipid phase transition parameters observed with age. Unsaturation could contribute to decreased tear film stability with age.

Comparison of non-invasive tear film stability measurement techniques

BACKGROUND

Measurement of tear film stability is commonly used to give an indication of tear film quality but a number of non-invasive techniques exists within the clinical setting. This study sought to compare three non-invasive tear film stability measurement techniques: instrument-mounted wide-field white light clinical interferometry, instrument-mounted keratoscopy and hand-held keratoscopy.

METHODS

Twenty-two subjects were recruited in a prospective, randomised, masked, cross-over study. Tear film break-up or thinning time was measured non-invasively by independent experienced examiners, with each of the three devices, in a randomised order, within an hour.

RESULTS

Significant correlation was observed between instrument-mounted interferometric and keratoscopic measurements (p < 0.001) but not between the hand-held device and the instrument-mounted techniques (all p > 0.05). Tear film stability values obtained from the hand-held device were significantly shorter and demonstrated narrower spread than the other two instruments (all p < 0.05), while no significant differences were observed between the two instrument-mounted devices (all p > 0.05).

CONCLUSION

Good clinical agreement exists between the instrument-mounted interferometric and keratoscopic measurements but not between the hand-held device and either of the instrument-mounted techniques. The results highlight the importance of specifying the instrument employed to record non-invasive tear film stability.