Interblink Interval Research Articles

Ocular thermography in ocular inflammation and dry eye

AbstractMeasurement of the ocular surface temperature (OST) has been proposed as a diagnostic method for ocular surface pathologies as dry eye disease (DED), due to the involvement in its pathophysiology of tear evaporation rate.During mild inflammation induced by UV radiation in guinea pigs, no changes in the initial OST measured immediately after eye opening and in the rate of OST decrease during the interblink interval (IBI) were observed. However, during allergic keratoconjunctivitis, where tearing and blinking were significantly increased and a prominent inflammation was induced, the initial OST was significantly increased.In animals with experimentally‐induced tear deficiency, a variability in the initial OST values was found: some animals showed a “cold spot” (increasing in intensity and size during IBI) in the central cornea, while in other animals initial OST was warmer than control, suggesting a subclinical inflammation.Eyes from Sjögren syndrome patients, besides a reduced tearing rate, showed higher initial OST and faster ocular surface cooling between blinks than eyes from age‐matched healthy subjects.Although OST values per se do not provide relevant information on ocular surface disease, due to the differences in etiology and pathophysiology of DED, it may be a valid diagnostic method if combined with the clinical evaluation of inflammation, and tear volume, composition and stability.Support: AEI‐ERDF SAF‐2017‐83674‐C2‐1‐R and 2‐R; Generalitat Valenciana PROMETEO/2018/114.

Analysis of Spontaneous Eyelid Blink Dynamics Using a 240 Frames per Second Smartphone Camera.

To report initial results using a native 240 frames per second smartphone camera for 2-dimensional videographic analysis of eyelid dynamics during spontaneous blinking. Spontaneous blinking was prospectively recorded in volunteers using a smartphone camera recording at 240 frames per second in 720p. A standardized recording setup was used in which the smartphone was mounted on a tripod stand at 0.5 m in the Frankfort horizontal plane. Subjects viewed a nature documentary video in primary gaze while their spontaneous blinking was recorded for 3 minutes. Exclusion criteria included known eyelid malposition or ocular surface pathology, including dry eye syndrome, contact lens use, prior eyelid or intraocular surgery, prior periocular trauma, or craniofacial abnormality. Primary outcome measures were spontaneous interblink interval, blink rate in blinks per minute, percentage of incomplete blinks, and blink velocity. The authors studied 10 subjects, 5 men and 5 women. Average age was 34 (range 19-58). Mean interblink interval was found to be 7.4 seconds (SD: 5.2, range: 1.9-17.6), corresponding to a mean blink rate of 13 blinks per minute (SD: 7.8, range: 3.4-32.0). Mean percentage of incomplete blinks was 49.8% (SD: 33.3, range: 0-100). Mean blink closure velocity was 93 mm/seconds (SD: 31, range: 40-160). These numbers are consistent with previously published results of spontaneous eyelid blink parameters. This study demonstrates that 240 frames per second videography native to modern smartphone cameras captures anatomic detail and blink dynamics with sufficient resolution and clarity to provide objective clinical information about spontaneous eyelid blink rate, dynamics, and function.

Blind working time in visual display terminal users.

ObjectivesBlind working (BW) time (time during which vision is not required), the interblink interval (IBI), and subjective symptoms were investigated in workers using visual display terminals (VDTs).Subjects and MethodsTo investigate BW time, 10 VDT users were instructed to close their eyes when this did not interfere with their work. They were video recorded for 60 minutes using a webcam attached to the display on which they were engaged in regular data input tasks, and BW time was measured. The values of the IBI during the final 20 minutes of the BW experiment and during the final 20 minutes of normal working without BW were compared. A questionnaire was administered to investigate subjective symptoms using a visual analogue scale.ResultsThe total BW time during the final 20‐minute period was 20.6‐121.0 seconds (1.7%‐10.1%). The mean IBI of 5.5 ± 4.5 seconds during the BW experiment was not significantly different from that of 6.2 ± 5.6 seconds during normal working, and the mean of three IBIs immediately after BW during the BW experiment was 2.7 ± 1.0 seconds, significantly shorter than the 6.2 ± 5.6 seconds during normal working. Dry eye, ocular fatigue, and blurred vision during normal working improved when subjects were engaged in BW.ConclusionsVDT users could engage in BW during VDT work, the IBI was shorter immediately after BW, and subjective symptoms improved. These results suggest that BW may provide a more effective measure for the management of VDT working time.

Corneal surface temperature decrease during the interblink interval is greater in Sjögren's syndrome

Corneal surface temperature decrease during the interblink interval is greater in Sjögren's syndrome

Clinical feasibility of pinhole glasses in presbyopia.

To investigate the ocular physiologic changes and subjective symptoms of wearing multiple-pinhole glasses in subjects with presbyopia. This prospective study included 32 eligible subjects with presbyopia. Objective ocular functions and a survey of ocular discomfort were performed at baseline. All participants underwent the same examinations after reading while wearing the pinhole glasses and not wearing these glasses at a 1-week interval in random order. The pinhole glasses improved uncorrected distance and near visual acuity in presbyopia. These glasses also required 15% less accommodative power over the near stimulus of 25 cm than did eyes without pinholes. Compared to reading without pinhole glasses, reading with pinhole glasses led to the following changes: increase in monocular near point of accommodation from 4.39 ± 0.78 diopter (D) to 5.19 ± 1.12 D, increase in depth of focus from 1.42 ± 0.44 D to 2.00 ± 0.33 D, and increase in amplitude of fusional convergence from 13.38 ± 6.88 prism D to 21.62 ± 10.00 prism D. In contrast, the reading speed decreased, inter-blink interval increased, tear break-up time shortened, and subjective ophthalmic symptoms worsened with pinhole glasses compared to without. In presbyopia, pinhole glasses improve visual acuity and accommodation-related parameters by pseudo-accommodation and the pinhole effect. However, the low legibility, increased inter-blink interval, and shortened break-up time of pinhole glasses cause an uncomfortable feeling and excessive eye fatigue. Pinhole glasses have strengths and limitations that must be considered to provide appropriate guidance in patients with presbyopia. Clinical trial registration was done at www.ClinicalTrials.gov (identifier: NCT02722291).

Threshold-varying integrate-and-fire model reproduces distributions of spontaneous blink intervals.

Spontaneous blinking is one of the most frequent human behaviours. While attentionally guided blinking may benefit human survival, the function of spontaneous frequent blinking in cognitive processes is poorly understood. To model human spontaneous blinking, we proposed a leaky integrate-and-fire model with a variable threshold which is assumed to represent physiological fluctuations during cognitive tasks. The proposed model is capable of reproducing bimodal, normal, and widespread peak-less distributions of inter-blink intervals as well as the more common popular positively skewed distributions. For bimodal distributions, the temporal positions of the two peaks depend on the baseline and the amplitude of the fluctuating threshold function. Parameters that reproduce experimentally derived bimodal distributions suggest that relatively slow oscillations (0.11–0.25 Hz) govern blink elicitations. The results also suggest that changes in blink rates would reflect fluctuations of threshold regulated by human internal states.

Spontaneous Eye Blink Patterns in Dry Eye: Clinical Correlations.

To evaluate spontaneous eye blink patterns and their correlations with clinical tests in dry eye disease (DED). Twenty-five DED patients and 25 healthy subjects were included in this prospective case-controlled study. Clinical evaluations included the Ocular Surface Disease Index (OSDI), lipid layer thickness (LLT), spontaneous eye blink pattern analysis, fluorescein tear film break-up time (FBUT), and so on. Eye blinks were recorded for 20 seconds with a high-speed camera. Eye blink patterns were divided into the following five phases: the eyelid closing phase (ECP), eyelid closed phase (CDP), early opening phase (EOP), late opening phase (LOP), and interblink intervals (IBI). The correlations between blink parameters and clinical tests were analyzed. Compared with the control group, mean ECP, CDP, and EOP were significantly longer in DED patients (P < 0.001, P = 0.029, and P < 0.001, respectively). DED patients also had significantly shorter LOP and blink intervals (both P < 0.001) and more partial blinks as compared with control subjects (P = 0.001). FBUT was negatively correlated with ECP (r = -0.618, P=0.001) and the number of partial blinks (r = -0.413, P = 0.040). There was a positive correlation between OSDI and the number of partial blinks (r = 0.446, P = 0.026). The LLT coefficient of variation (LLT-CV) also showed a positive correlation with ECP, CDP, and LOP (P = 0.001, P = 0.050, P = 0.049, respectively). Corneal and conjunctival staining was positively correlated with ECP, CDP, and the number of blinks (r = 0.449, P = 0.024; r = 0.526, P = 0.007; r = 0.456, P = 0.022, respectively) and negatively correlated with IBI (r = -0.420, P = 0.037). Partial blinks, prolonged eyelid closed time and short blink intervals were the three main characteristics of DED patients' spontaneous blink patterns.

Group size effects on inter-blink interval as an indicator of antipredator vigilance in wild baboons

Vigilance in animals is an important means for predator detection. Animals living in groups reduce their predation risk as more individuals are present. In contrast to most other animals studied, many studies on primates do not support the prediction that individual vigilance will decline as group size increases. For animals to obtain visual information during vigilance behaviour, their eyes must be open. Therefore, if animals are able to perceive differential risk of predation, the inter-blink interval (eye-opening) should increase, and the blink duration (eye-closure) should decrease under higher predation risk. We tested this prediction by measuring inter-blink interval in wild anubis baboons (Papio anubis) in peripheral and centre individuals within a group, and between larger and smaller groups. We found that the inter-blink interval for young males, often located at the front edge of the group, was longer than that of adult males, adult females, and young females, often located in the center of the group, and that the inter-blink interval for adult males was longer when the group was smaller. These results suggest that inter-blink interval can be used as an indicator of primate vigilance toward predators.

Post-blink tear film dynamics in healthy and dry eyes during spontaneous blinking

PurposeThe aim was to investigate the dynamics of post-blink tear film leveling in natural blinking conditions (NBC) for healthy subjects and those diagnosed with dry eye syndrome (DES) and to relate this phase to the tear film surface quality (TFSQ) before the following blink. MethodsThe study included 19 healthy persons and 10 with dry eye, grouped according to symptoms and signs observed during examination. Lateral shearing interferometry was used to examine TFSQ. Post-blink tear film dynamics was modeled by an exponential function, characterized by the decay parameter b, and a constant, describing the level of the stabilized TFSQ. Pre-next-natural-blink TFSQ dynamics was modeled with a linear trend, described by a parameter A. ResultsThe post-blink tear film dynamics reached its plateau at a significantly (P = 0.006) lower level in the normal tear film group than in the dry eye group. The median exponential decay parameter b was statistically significantly higher for the control group than for the DES group, P = 0.026. The parameter b calculated for each interblink interval was significantly correlated with the corresponding parameter A (Spearman's R = 0.35; P < 0.001). Correlation between the median b and tear film fluorescein break-up time for each subject was also found (R = 0.41, P = 0.029). ConclusionsSignificantly faster leveling of post-natural-blink tear film was observed in the group with DES than in healthy eyes. This dynamic was correlated with the pre-next-natural-blink TFSQ and tear film stability. The results of this pilot study support previous works that advocate the importance of polar lipids in the mechanism of tear film lipid spreading.

A novel eyelid motion monitor.

Eyelid motion analysis can provide important information about ophthalmic, neurologic, and systemic diseases. Routine assessment of eyelid function is currently based mainly on clinical examination estimating Levator Function and static palpebral fissure measurements. Most clinical tools developed to date are cumbersome expensive and difficult to operate. Currently there is no widely available, affordable device providing user friendly precision based evaluation of eyelid kinematics. Our goal is to develop a novel device for evaluation of eyelid kinematics providing rapid defined diagnosis of diseases involving eyelid movement. A real-time prototype eyelid motion monitoring system was designed based on magnetic field sensors detecting movement of a tiny magnet located on the upper eyelid. Motion is recorded and analyzed using specially developed hardware and software, respectively, enabling both real-time and off-line data presentation. The Eyelid Motion Monitor correlates between blinking characteristics of eyelid movement and the output voltages produced by the system. Blink detection is defined as peak in voltage, caused by eyelid closure or opening. The device was tested on 20 healthy volunteers with normal clinical blinking patterns. The Eyelid Motion Monitor succeeded in detecting full blink motion. The system easily extracts different parameters of eyelid kinetics. An inexpensive prototype novel device was developed for monitoring and analyzing eyelid motion characteristics, including the inter-blink interval, eye closing/opening duration and entire blink duration. The device should allow early objective non- invasive diagnosis and follow-up of disease progression. It could be of great potential value in many ophthalmic, neurologic, and systemic diseases.

Diurnal Tracking of Blink and Relationship to Signs and Symptoms of Dry Eye.

To assess diurnal changes in the signs and symptoms of dry eyes and their relationship to diurnal interblink interval (IBI) in normal subjects and in subjects with dry eye. Blink data were collected from 9:00 AM to 8:00 PM during 2 days of normal activity using an electrocardiogram monitoring device. All subjects recorded ocular discomfort (0-5 scale) and primary activity hourly each day in a diary. Inferior and central fluorescein staining was graded by slit lamp (0-4) at the start and end of each day. Blink activity was detected using an algorithm based on recognition of the waveform corresponding to the kinematic properties of the blink signal. Normal subjects (N = 12) reported negligible symptoms, and results did not show a diurnal change in group hourly IBI. Mean daily IBI for the group with dry eye (N = 15) (4.63 ± 1.63 s) was shorter than that for the normal group (5.28 ± 1.48 s) (P = 0.0483). Correlation of diurnal symptoms and mean hourly IBI was relatively weak (r = -0.248). A repeated-measures model found IBI to be significantly associated with the time of day (P = 0.0028). Inferior corneal staining showed a small but significant diurnal increase for both normal group and group with dry eyes. Diurnal blink tracking reveals significant trending with symptoms. Diurnal change in IBI may be an appropriate surrogate for symptoms in the study of dry eye.

Temperatures of the Ocular Surface, Lid, and Periorbital Regions of Sjögren's, Evaporative, and Aqueous-Deficient Dry Eyes Relative to Normals

PurposeTo compare the temperatures of the ocular surface, eyelid, and periorbital skin in normal eyes with Sjögren's syndrome (SS) eyes, evaporative dry eyes (EDE), and aqueous deficient dry eyes (ADDE). Methods10 eyes were analyzed in each age-matched group (normal, SS, EDE, and ADDE). A noninvasive infrared thermal camera captured two-dimensional images in three regions of interest (ROI) in each of three areas: the ocular surface, the upper eyelid, and the periorbital skin within a controlled environmental chamber. Mean temperatures in each ROI were calculated from the videos. Ocular surface time-segmented cooling rates were calculated over a 5-s blink interval. ResultsRelative to normal eyes, dry eyes had lower initial central OSTs (SS −0.71°C, EDE −0.55°C, ADDE −0.95°C, KW P<.0001) and lower central upper lid temperatures (SS −0.24°C, ADDE −0.51°C, and EDE −0.54°C, KW P<.0001). ADDE eyes had the lowest initial central OST (P<.0001), while EDE eyes had the lowest central lid temperature and lower periorbital temperatures (P<.0001). Over the 5-s interblink interval, the greatest rate of temperature loss occurred following eyelid opening, but varied by group (normals −0.52, SS −0.73, EDE −0.63, and ADDE −0.75°C/s). The ADDE group also had the most substantial heat loss over the 5-s interblink interval (−0.97°C). ConclusionsDifferences in OST may be related to thermal differences in lids and periorbita along with an altered tear film. Thermography of the ocular surface, lids, and surrounding tissues may help to differentiate between different etiologies of dry eye.

How Blink Anomalies Can Contribute to Post-LASIK Neurotrophic Epitheliopathy

: Post-LASIK (laser in situ keratomileusis) symptoms and signs of dry eye have multiple causes. For example, tear osmolarity and the concentration of inflammatory mediators can increase because of reduced aqueous production and increased evaporative loss as a result of lower blink rates and increased interblink intervals. The tear concentration of inflammatory mediators can also increase because of surgical trauma, wound healing, comorbid systemic and ocular diseases, and the use of punctal plugs. Studies that examine only mechanical sensitivity of the cornea cannot detect changes in chemical sensitivity, which can persist longer. Symptoms may be partly attributed to sensitization of the traumatized corneal or lid wiper sensory nerves by inflammatory mediators. Increased lid wiper sensitivity could increase awareness of blinks, especially if ocular surface lubricity is reduced. Incomplete blinks have been found to represent 10 to 22% of the total number of blinks. Loss of neural stimuli and lower blink rates increase the significance of incomplete blinks that approximately double related interblink intervals and tear evaporation. The most common location of post-LASIK epitheliopathy is the inferior area of the cornea, which is overexposed by incomplete blinks. The relevance of incomplete blinking to post-LASIK epitheliopathy is supported by the relative absence of this complication in the similarly neurotrophically disadvantaged upper corneal areas for which blink rates and other tear functions usually appear to be adequate to prevent epitheliopathy, which stains. Occupational or leisure-time activities such as computer use and reading, which have been found to reduce blink rates and blink completeness, appear to be significant risk factors for symptoms and signs of dry eye. Apart from reducing symptoms and signs of dry eye, prophylactic and post-LASIK blink exercises to reduce incomplete blink rates and associated overexposure of the ocular surface may also contribute to more accurate refractive outcomes through faster wound healing.

The Effect of Tear Supplementation on Ocular Surface Sensations during the Interblink Interval in Patients with Dry Eye.

PurposeTo investigate the characteristics of ocular surface sensations and corneal sensitivity during the interblink interval before and after tear supplementation in dry eye patients.MethodsTwenty subjects (41.88±14.37 years) with dry eye symptoms were included in the dry eye group. Fourteen subjects (39.13±11.27 years) without any clinical signs and/or symptoms of dry eye were included in the control group. Tear film dynamics was assessed by non-invasive tear film breakup time (NI-BUT) in parallel with continuous recordings of ocular sensations during forced blinking. Corneal sensitivity to selective stimulation of corneal mechano-, cold and chemical receptors was assessed using a gas esthesiometer. All the measurements were made before and 5 min after saline and hydroxypropyl-guar (HP-guar) drops.ResultsIn dry eye patients the intensity of irritation increased rapidly after the last blink during forced blinking, while in controls there was no alteration in the intensity during the first 10 sec followed by an exponential increase. Irritation scores were significantly higher in dry eye patients throughout the entire interblink interval compared to controls (p<0.004). NI-BUT significantly increased after HP-guar (p = 0.003) but not after saline drops (p = 0.14). In both groups, either after saline or HP-guar the shape of symptom intensity curves remained the same with significantly lower irritation scores (p<0.004), however after HP-guar the decrease was significantly more pronounced (p<0.004). Corneal sensitivity to selective mechanical, cold and chemical stimulation decreased significantly in both groups after HP-guar (p<0.05), but not after saline drops (p>0.05).ConclusionOcular surface irritation responses due to tear film drying are considerably increased in dry eye patients compared to normal subjects. Although tear supplementation improves the protective tear film layer, and thus reduce unpleasant sensory responses, the rapid rise in discomfort is still maintained and might be responsible for the remaining complaints of dry eye patients despite the treatment.

Non invasive assessment of the human tear film dynamics

Dry eye disease, or keratoconjunctivitis sicca, is a multifactorial syndrome with altered tear film homeostasis leading to ocular irritations. These alterations cause discomfort and stress for the patient, but only a few objective parameters allow for proper differential diagnosis into different subtypes of this condition. The mostly invasively performed standard assessment procedures for tear film diagnosis are manifold, but often correlate quite poorly with the subjectively reported symptoms. Due to the inherent limitations, e.g. the subjectivity of the commonly performed invasive tests, a number of devices have been developed to assess the human tear film non-invasively. Since the production, delivery, distribution and drainage of the tear film is a dynamic process, we have focused our review on non-invasive methods which are capable of continuous or repetitive observations of the tear film during an inter-blink interval. These dynamic methods include (1) Interferometry, (2) Pattern Projection, (3) Aberrometry, (4) Thermography; and (5) Evaporimetry. These techniques are discussed with respect to their diagnostic value, both for screening and differential diagnostic of Dry Eye Disease. Many of the parameters obtained from these tests have been shown to have the potential to reliably discriminate patients from healthy subjects, especially when the tests are performed automatically and objectively. The differentiation into subtypes based solely on a single, dynamic parameter may not be feasible, but the combination of non-invasively performed procedures may provide good discrimination results.

The Effects of Increasing Ocular Surface Stimulation on Blinking and Tear Secretion.

To investigate the effect of varying levels of ocular surface stimulation on the timing and amplitude of the blink and tear secretion. Following instillation of fluorescein dye, increasing levels of air flow were directed toward the central corneas of 10 healthy subjects. Interblink interval (IBI), tear meniscus height (TMH), and fluorescence intensity were measured simultaneously. Because blinking can obscure changes in TMH, we developed novel measures of tear secretion by calculating tear meniscus fluorescein concentration (TMFC) from intensity using a mathematical model. The change of TMH and TMFC over trials and the slope of the TMFC within each IBI (IBI-TTR) were further calculated. The mean IBI was decreased by 8.08 ± 8.54 seconds from baseline to maximum air stimulation. The TMH increase was highly variable (0.41 ± 0.39 mm) among subjects, compared to the fluorescence tear turnover metrics: decrease in TMFC of 2.84 ± 0.98 natural logarithm or ln(%) and IBI-TTR of 0.065 ± 0.032 ln(%)/sec. Ocular surface stimulation was highly correlated with the TMFC and IBI-TTR, but less so with TMH (Pearson's r = 0.71, 0.69, and 0.40, P < 0.01, respectively). Blinking and tearing were significantly correlated with each other (Pearson's r = 0.56, P < 0.01), but tearing lagged behind by an average of 6.54 ± 4.07 seconds. Blinking and tearing share a common origin with sensory stimulation at the ocular surface. Both showed a dose-response increase with surface stimulation and were correlated with each other. These methods can potentially be used to understand alterations in ocular surface sensory function and associated protective responses in dry eye and other disorders of the ocular surface.

The heritability of dry eye disease in a female twin cohort.

We estimated the relative importance of genes and environment in dry eye disease (DED) using a classic twin study. A large sample of 3930 female monozygotic and dizygotic twins from the UK Adult Twin Registry (TwinsUK) was questioned about the presence of a DED diagnosis and about DED symptoms in the preceding 3 months. In addition, a subset of 606 twins was examined for several dry eye signs. Genetic and environmental effects were estimated using maximum likelihood structural equation modeling. All DED outcome variables showed higher correlation in monozygotic twin pairs than in dizygotic twin pairs, suggesting genes have a contributory role in DED. The DED symptoms showed a heritability of 29% (95% confidence interval [CI], 18%-40%). A clinician's diagnosis of DED with concurrent use of artificial tears showed a heritability of 41% (95% CI, 26%-56%). Estimates of the heritability of DED signs were 25% (95% CI, 7%-42%) for interblink interval, 58% (95% CI, 43%-70%) for Schirmer value, 40% (95% CI, 25%-53%) for tear osmolarity, and 78% (95% CI, 59%-90%) for the presence of blepharitis. The unique environment explained the remainder of the variance. We found no significant heritability for tear breakup time. Genetic factors contribute moderately to the diagnosis, symptoms, and the signs of DED. Compared to other ocular phenotypes, the lower heritability might reflect some of the difficulties in objective phenotyping of DED in a population-based sample. However, future genetic studies are now justified and may help in unraveling the pathophysiology of DED.

Withdrawal of voluntary inhibition unravels the off state of the spontaneous blink generator

Involuntary movements such as spontaneous eye blinks can be successfully inhibited at will. Little do we know how the voluntary motor circuits countermand spontaneous blinks. Do the voluntary inhibitory commands act to pause or to turn off the endogenous blink generator, or does inhibition intersect and counter the generator׳s excitatory outputs? In theory, the time taken for the system to generate an after-inhibition blink will reflect onto the form of inhibition. For instance, if voluntary commands were to turn the blink generator off then the after-blink latency would be fixed to the inhibition offset and reflect the time it takes for the generator to rebound and turn on. In this study we measured the after-blink latency from the offset of voluntary inhibition. Volunteers inhibited their blinks in response to sound tones of randomly varying durations. At the offset volunteers withdrew the inhibition and relaxed. Interestingly, the spontaneous after-blinks were fixed to the offset of the inhibition as if the generator rebounded from an off state. The after-blink latency was not related to the duration of the inhibition, and inhibiting even for a small fraction of the mean inter-blink interval generated an after-blink time-locked to the inhibition offset. Interestingly, the insertion of voluntary blinks after inhibition further altered the blink generator by delaying the spontaneous after-blinks. We propose that the inhibition of spontaneous blinks at the level of the generator allows for highly effective voluntary countermanding. Nevertheless, the withdrawal of such inhibition was strongly associated with motor excitation.

Eye Movements of Dry Eye (DE) Patients During Reading.

Introduction: A recent epidemiological study indicated that DE patients report that reading is a difficult task (odds ratio 3.64, p <0.0001). In addition, studies have demonstrated that DE patients read slower than normal controls. However, there are no reported studies that have monitored eye movements of DE patients while they read. The purpose of this study was to investigate if specific eye movement parameters are altered during reading in DE patients. Methods: Seventeen subjects took part in this study (10 DE (age 63.2 ± 6.16) and 7 normal controls (age 61.3 ± 7.01)). All subjects had a complete eye exam with DE work up. DE patients had both subjective and objective signs of a DE in compliance with the recommendations of the 2007 International Dry Eye Workshop. The Tobii TX300 Eye Tracker monitored eye movements (saccades, fixations, regressions, and blinks) during reading. The Wilkins Rate of Reading Test was used to determine reading rate. Results: There were no significant differences between DE patients and normal controls for saccade amplitude, saccade velocity, fixation time, number of saccades or fixations, or number of regressions (all p values > 0.05). The reading rates were also not different between the groups (DE = 152.6 ± 13.4 wpm, Control =159 ± 13.2 wpm, p = 0.34). The DE patients had more total blinks (DE = 21.0 ± 8.18, Control = 5.29 ± 2.69, p <0.001) and a shorter inter-blink interval (DE = 3.3 ± 2.04 sec, Control = 14.9 ± 8.54 sec, p = 0.013) than the normal controls. Conclusions: The increased number of blinks and the shorter inter-blink interval while reading may result in a slower reading rate and a greater difficulty reading for DE subjects. Meeting abstract presented at VSS 2014

The Effects of Increasing Ocular Surface Stimulation on Blinking and Sensation

The purpose of this study was to determine how increasing ocular surface stimulation affected blinking and sensation, while controlling task concentration. Ten healthy subjects concentrated on a task while a custom pneumatic device generated air flow toward the central cornea. Six flow rates (FRs) were randomly presented three times each and subjects used visual analog scales to record their sensory responses. The interblink interval (IBI) and the FR were recorded simultaneously and the IBI, sensory response, and corresponding FR were determined for each trial. The FR associated with a statistically significant decrease in IBI, the blink increase threshold (BIT), was calculated for each subject. Both the mean and SD of IBI were decreased with increasing stimulation, from 5.69 ± 3.96 seconds at baseline to 1.02 ± 0.37 seconds at maximum stimulation. The average BIT was 129 ± 20 mL/min flow rate with an IBI of 2.33 ± 1.10 seconds (permutation test, P < 0.001). After log transformation, there was a significant linear function between increasing FR and decreasing IBI within each subject (Pearson's r ≤ -0.859, P < 0.05). The IBI was highly correlated with wateriness, discomfort, and cooling ratings (Pearson's r ≤ -0.606, P < 0.001). There was a dose-response-like relationship between increased surface stimulation and blinking in healthy subjects, presumably for protection of the ocular surface. The blink response was highly correlated with ocular surface sensation, which is not surprising given their common origins. The BIT, a novel metric, may provide an additional end point for studies on dry eye or other conditions.