Blinking and corneal sensitivity

Eye complaints in the office environment: precorneal tear film integrity influenced by eye blinking efficiency

To achieve a common base for understanding work related eye complaints in the office environment, it is necessary to merge approaches from indoor air science, occupational health, and ophthalmology. Based on database searches, it is concluded that precorneal tear film (PTF) alteration leads to eye complaints that may be caused by: (1) thermal factors (low relative humidity; high room temperature); (2) demanding task content (attention decreases blinking and widens the exposed ocular surface area); and (3) individual characteristics (for example, tear film alterations, blinking anomalies, gland dysfunctions, and use of contact lenses). These factors and conditions are able to progressively increase water evaporation and faster thinning of the PTF, which causes dryness and dry spot formation on the cornea, possibly followed by corneal and conjunctiva epithelial alterations and eye complaints. Another possible cause of eye complaints is certain irritating chemical compounds, in addition to oxidation mixtures that are formed in reactions between ozone and unsaturated organic compounds (alkenes). The effect may be exacerbated by low relative humidity.

Ocular Surface Changes in Laser in situ Keratomileusis-induced Neurotrophic Epitheliopathy

PURPOSE

To evaluate the ocular surface changes in patients with laser in situ keratomileusis (LASIK)-induced neurotrophic epitheliopathy.

METHODS

Seven consecutive patients with LASIK-induced neurotrophic epitheliopathy were studied prospectively and compared to a control group (seven consecutive patients who had LASIK- but without neurotrophic epitheliopathy). Bilateral sequential LASIK was performed at a 1-week interval; the first operated eye of each patient was considered for statistical analysis. Blinking, corneal sensitivity, tear break-up time, tear secretion and clearance were measured preoperatively (T0) and postoperatively at 1 week after surgery on the first eye (T1), and 1 week (T2), 1 month (T3), and 3 months (T4) after surgery was performed on the second eye.

RESULTS

Laser in situ keratomileusis-induced neurotrophic epitheliopathy occurred bilaterally in all patients. During follow-up, patients with LASIK-induced neurotrophic epitheliopathy showed a significant decrease in blinking (P = .0002), which was not observed in cases without LASIK-induced neurotrophic epitheliopathy [corrected] Compared to eyes without LASIK-induced neurotrophic epitheliopathy, those with LASIK-induced neurotrophic epitheliopathy revealed lower values of sensitivity in the central cornea preoperatively and early postoperatively (T0, P = .004; T1, P = .003; T2, P = .003). A trend towards reduced sensitivity was also detected in the central cornea in late follow-up and in the superior, temporal, and nasal sectors of the flap at all examinations. No significant differences were observed in break-up time, tear secretion, or clearance within or between the two groups.

CONCLUSION

Decreased blinking seems to be involved in the pathogenesis of LASIK-induced neurotrophic epitheliopathy. The reduction probably depends on the lower levels of corneal sensitivity and induces the epitheliopathy by increasing the ocular surface exposure.

Early changes in corneal sensation, ocular surface integrity, and tear-film function after laser-assisted subepithelial keratectomy

PURPOSE

To investigate the changes in corneal sensation, ocular surface integrity, and tear-film function after laser-assisted subepithelial keratectomy (LASEK).

SETTING

Department of Ophthalmology, University of Graz, Graz, Austria.

METHODS

Laser-assisted subepithelial keratectomy was performed in 21 consecutive patients (37 myopic eyes). The patients were observed for subjective complaints of dry eye, corneal sensation, tear-film breakup time (BUT), Schirmer test without local anesthesia, and fluorescein and lissamin-green staining preoperatively and 1 week and 1, 3, and 6 months postoperatively.

RESULTS

The subjective score for dry-eye symptoms was not statistically significantly higher after the procedure. Corneal sensation was reduced up to 1 month after LASEK (P<.05). There were obvious decreases in BUT at 1 week and 1 month (P<.01) and no significant changes in Schirmer test results. In fluorescein staining of the cornea, dots were more concentrated at 1 week (P<.05). In lissamin-green staining, no significant changes were found at any follow-up examination.

CONCLUSIONS

Laser-assisted subepithelial keratectomy induced a short-term reduction in corneal sensation and affected the ocular surface and tear film slightly. Epithelial flap repositioning in LASEK may have a positive influence on tear-film and ocular-surface factors.

An assessment of the pattern of spontaneous eyeblink activity under the influence of topical ocular anaesthesia

PURPOSE

To determine whether there is a change in the pattern of human eyeblink events under topical ocular anaesthesia.

METHODS

Forty male subjects, aged between 19 and 52 years and with no significant ocular surface disease, were recruited. Their spontaneous eyeblink activity, in primary eye gaze position and in silence, was recorded for 5-min periods, before and after instillation of benoxinate 0.4% eyedrops. The surface anaesthesia was confirmed by aesthesiometry.

RESULTS

The spontaneous eyeblink rate (SEBR) decreased from 9.1+/-4.0 blinks/min to an average of 5.7+/-3.3 blinks/min, with 37 subjects showing a decreased eyeblink rate under anaesthesia. Three blink patterns were observed before anaesthesia (symmetrical, J-type and I-type) and these were essentially unchanged under anaesthesia.

CONCLUSIONS

These studies confirm that the SEBR is usually reduced under surface anaesthesia (so is sensitive to exogenous control) but the pattern of the eyeblink activity is unchanged (so is less sensitive to exogenous control). The removal of exogenous stimuli by anaesthesia does not shift the eyeblink pattern to a single type, so indicates endogenous control.

Changes in the tear film and ocular surface from dry eye syndrome

Dry eye syndrome (DES) refers to a spectrum of ocular surface diseases with diverse and frequently multiple aetiologies. The common feature of the various manifestations of DES is an abnormal tear film. Tear film abnormalities associated with DES are tear deficiency, owing to insufficient supply or excessive loss, and anomalous tear composition. These categorizations are artificial, as in reality both often coexist. DES disrupts the homeostasis of the tear film with its adjacent structures, and adversely affects its ability to perform essential functions such as supporting the ocular surface epithelium and preventing microbial invasion. In addition, whatever the initial trigger, moderate and severe DES is characterized by ocular surface inflammation, which in turn becomes the cause and consequence of cell damage, creating a self-perpetuating cycle of deterioration. Progress has been made in our understanding of the aetiology and pathogenesis of DES, and these advances have encouraged a proliferation of therapeutic options. This article aims to amalgamate prevailing ideas of DES development, and to assist in that, relevant aspects of the structure, function, and production of the tear film are reviewed. Additionally, a synopsis of therapeutic strategies for DES is presented, detailing treatments currently available, and those in development.

Management of the Ocular Surface and Tear Film Before, During, and After Laser in situ Keratomileusis

PURPOSE

To identify evidence-based, best practice strategies for managing the ocular surface and tear film before, during, and after laser in situ keratomileusis (LASIK).

METHODS

After a comprehensive review of relevant published literature, evidence-based recommendations for best practice management strategies are presented.

RESULTS

Symptoms of ocular irritation and signs of dysfunction of the integrated lacrimal gland/ocular surface functional gland unit are common before and after LASIK. The status of the ocular surface and tear film before LASIK can impact surgical outcomes in terms of potential complications during and after surgery, refractive outcome, optical quality, patient satisfaction, and the severity and duration of dry eye after LASIK. Before LASIK, the health of the ocular surface should be optimized and patients selected appropriately. Dry eye before surgery and female gender are risk factors for developing chronic dry eye after LASIK. Management of the ocular surface during LASIK can minimize ocular surface damage and the risk of adverse outcomes. Long-term management of the tear film and ocular surface after LASIK can reduce the severity and duration of dry eye symptoms and signs.

CONCLUSIONS

Strategies to manage the integrated ocular surface/lacrimal gland functional unit before, during, and after LASIK can optimize outcomes. As problems with the ocular surface and tear film are relatively common, attention should focus on the use and improvement of evidence-based management strategies.

The neonatal tear film

The importance of the tear film for the integrity of the ocular surface is well established. Full-term neonates produce tears normally, but low spontaneous blink rates during early life raises important questions regarding tear dynamics and stability. Although an afferent neural pathway that could potentially detect tear break-up is in place at birth, there is indirect evidence that the neonatal tear film is adapted to resist evaporation-mediated tear thinning. This adaptation presumably prevents drying of the ocular surface during long inter-blink periods. However, low rates of tear turnover may have important implications for the defence of the eye against potential pathogens.

Validation of confocal microscopy through focusing for corneal sublayer pachymetry

PURPOSE

To evaluate the accuracy and precision of confocal microscopy through focusing (CMTF) for corneal sublayer pachymetry.

METHODS

A tandem scanning confocal microscope equipped with a nonapplanating contact objective was used to perform CMTF. The accuracy of CMTF measurements was evaluated using nine custom-made calibration contact lenses (PMMA) with varying thickness (300-600 microm) and radius of curvature (7.0-9.0 mm). The influence of immersion fluid stabilization and the consequence of prolonged corneal examination were assessed by performing CMTF in rabbits. Additionally, factors related to the instrumental setup and to sedation of experimental animals were examined.

RESULTS

For all calibration contact lenses, the thickness measured by CMTF was within +/-1.0 microm of the certified value. Varying the target thickness or radius of curvature had no consistent impact on the high accuracy of CMTF. When performing CMTF in vivo, z-axis motion was readily identified by sampling and comparing both in- and out-scans. Apart from involuntary eye movements, z-axis motion was due to initial thinning of the immersion fluid with stabilization obtained after approximately 1.5 minutes. Continued confocal examination led to slight but significant swelling of both the stroma (0.5 microm/min) and epithelium (0.1 microm/min).

CONCLUSIONS

CMTF is an accurate and precise technique for corneal sublayer pachymetry with concurrent display of cellular morphology. The precision of CMTF can be improved by allowing time for methylcellulose stabilization and by performing repeated two-way (in and out) scans to account for z-axis motion.

Evaluation of Tear Film Following Intacs for Myopia

PURPOSE

To evaluate the effect of intrastromal corneal ring segments (Intacs, Keravision) placement on the tear film quality as a measure of dry eye status.

METHODS

Seventeen eyes of ten patients underwent Intacs placement for the correction of myopia with spherical equivalent refractions ranging from -1.75 to -3.25 D (mean, -2.43 +/- 0.56 D). Dry eye grade values were measured preoperatively and at 1 day, 1 week, and 1 month postoperatively using the Kowa-DR-1 interferometer.

RESULTS

Preoperatively, the 17 eyes had a mean dry eye grade of 2.18 +/- 0.39 (range, 2 to 3). One day postoperatively, the 14 eyes measured had a mean dry eye grade of 2.64 +/- 0.63 (range, 2 to 4; P = .03). At 1 week the 17 eyes had a mean dry eye grade of 2.41 +/- 0.71 (range, 2 to 4; P = .25) and at 1 month, 2.18 +/- 0.39 (range, 2 to 3; P = .75).

CONCLUSIONS

There was transient dry eye following Intacs placement, but the tear film quality was restored within 1 week of surgery.

Effect of Laser in situ Keratomileusis for Hyperopia on Tear Film and Ocular Surface

PURPOSE

To examine the effects of laser in situ keratomileusis (LASIK) for hyperopia on the tear film and ocular surface.

METHODS

A retrospective 12-month analysis of 88 eyes (88 participants) who had LASIK for hyperopia was performed. Participants were evaluated before and after (2 weeks, 1, 3, 6, and 12 months) surgery for dry eye symptoms (McMonnies Dry Eye Survey primary symptoms), tear film stability (fluorescein break-up time), tear volume (phenol red thread test), ocular surface staining (fluorescein), and conjunctival goblet cell density.

RESULTS

Chronic dry eye was experienced by 32% of participants; symptoms were significantly associated with female gender, preoperative dry eye symptoms, lower tear film stability after surgery, greater ocular surface staining after surgery, lower tear volume before and after surgery, and lower goblet cell densities after surgery. Regression rate 12 months after surgery was 32% and significantly associated with female gender, chronic dry eye symptoms, lower tear film stability after surgery, greater ocular surface staining before and after surgery, and lower tear volume before and after surgery.

CONCLUSIONS

Dry eye, particularly in females, is problematic after LASIK for hyperopia and is associated with refractive regression. Current methods for managing the tear film and ocular surface may not control LASIK-induced dry eye, particularly in some females during the first 6 months after surgery.

Consideration of three types of spontaneous eyeblink activity in normal humans: during reading and video display terminal use, in primary gaze, and while in conversation

PURPOSE

To consider the conditions under which the so-called spontaneous (endogenous) eyeblink activity has been assessed by different investigators over the last 75 years and to consider the most appropriate terminology. The reason for this analysis was to try to identify why such different values for the spontaneous eyeblink rate (SEBR) have been reported.

METHODS

A retrospective evaluation of published articles was carried out to identify whether the SEBR assessments were consistently dependent on the activity of the subjects while spontaneous eyeblink activity was being investigated. These were compared with assessments of SEBR in young adult subjects under equivalent conditions.

RESULTS

Assessments of spontaneous eyeblink activity revealed that SEBR in a reading posture is lower than that in primary gaze, and SEBR is higher when subjects are in conversation. Such differences are also generally found in literature reports, especially if the primary gaze assessment is carried in silence. Electrophysiological measures of SEBR yield slightly higher values compared with observational techniques. Statistical analysis (with calculation of 95% confidence interval values) indicate that reading-SEBR should be between 1.4 and 14.4 eyeblinks/min, primary gaze-SEBR between 8.0 and 21.0 eyeblinks/min and conversational-SEBR between 10.5 and 32.5 eyeblinks/min for normal adults.

CONCLUSIONS

It is inappropriate to simply state a value for spontaneous eyeblink rate because it is so dependent on experimental conditions. It is further proposed that reports of SEBR measures should be prefixed by these experimental conditions, namely reading-SEBR, primary gaze-SEBR (in silence) and conversational-SEBR.

Dry eye after refractive surgery

Photorefractive keratectomy and laser in situ keratomileusis can induce or exacerbate dry eye after surgery. This manifests as an increase in degree and frequency of symptoms, corneal findings, such as superficial punctate keratopathy, and abnormal results of dry eye tests, such as the Schirmer test and tear break-up time. The cause mainly involves decreased corneal sensation, resulting in decreased feedback to the lacrimal gland and reduced tear production. Other causes may include increased evaporation, inflammation, or toxicity of medications. Dry eye may result infrequently in impaired wound healing and decreased optical quality of the cornea, but it is transient, lasting from a few weeks up to 1 year. Patients should be warned about this distressing complication. During a period of dry eye, artificial tears and punctal plugs are helpful in preventing or alleviating patient discomfort.

Corneal Sensitivity and Some Properties of the Tear Film After Laser in situ Keratomileusis

PURPOSE

To investigate central corneal sensitivity, lipid layer structure of the precorneal tear film, and tear volume after laser in situ keratomileusis (LASIK).

METHODS

Central corneal sensitivity was measured using the Non-Contact Corneal Aesthesiometer. The aesthesiometer was mounted on a slit lamp and an airpulse of controlled pressure was directed onto the cornea. When central corneal sensitivity was reduced, a higher air pulse pressure was required to stimulate the cornea. The final central corneal sensitivity threshold measured was recorded in millibars. Tear lipid layer structure was assessed by optical interferometry and classified according to appearance using the Keeler Tearscope. Tear volume was measured using the phenol red cotton thread test. Subjects were recruited from a group of patients after LASIK who had experienced no complications (n=22). The average postoperative time was 14 weeks and measurements were taken on one eye. In bilateral cases, measurements were recorded from the right eye only. Average attempted correction was -6.30 D (range, -2 to -11 D). Age-matched controls were later recruited for central corneal sensitivity threshold (n=24). A second group of age-matched controls were recruited for tear volume and lipid layer structure (n=24).

RESULTS

The median (range) was 1.1 mbars (0.2 to 4.3 mbars) after LASIK and 0.58 mbars (0.20 to 1.3 mbars) in the controls; the difference was statistically significant (P = .043). The lipid layer of the tear film tended to be thinner in eyes after LASIK compared with controls (P = .032). The mean (+/- SD) tear volume was 16.9 +/- 8.3 mm after LASIK and 19.8 +/- 7.1 mm in controls. This difference was not statistically significant (P = .492).

CONCLUSION

At 14 weeks postoperatively, central corneal sensitivity was below normal levels and the tear lipid layer was thinner. The poorer quality lipid layer may predispose to symptoms of dry eye after LASIK.

Relation between tear breakup time and spontaneous blink rate

Blinking plays an important role in maintaining corneal integrity by spreading of the tear film. Although there are studies reporting on blink rate and tear stability, a consensus has not been reached. Therefore, the blink rate and tear breakup time (TBUT) test were performed in 159 healthy young females. The mean TBUT and blink rate values observed were 18.9 seconds and 18.6 blinks/min, respectively. A significant correlation (r = 0.74, p < 0.05) between TBUT and blink rate was found. These results demonstrate that blink rate may be dependent on TBUT, at least among subjects with TBUT less than 19 seconds. Thus, blink rate may depend not only on cortical stimuli but also on the stability of the tear film.

Frequent association of delayed tear clearance in ocular irritation

AIM

To explore the pathogenic role of delayed tear clearance.

METHODS

By comparing 10 patients with punctal obstruction and 20 asymptomatic normals, delayed tear clearance was diagnosed in 70 patients without apparent punctal obstruction using fluorescein clearance test.

RESULTS

The majority were older (71.4 (SD 1.2) years) and women (66%). Frequent complaints included redness, itching, mucus discharge, and crusting, which tended to be worse upon awakening. Common associated problems were medicamentosa (13%), drug induced pseudopemphigoid, ocular hypertension (27%), and glaucoma (7%). Topical non-preserved 1% methylprednisolone resulted in subjective (83%) and objective (80%) improvement and resolution of delayed tear clearance (87%).

CONCLUSION

These results indicate strong association of delayed tear clearance with intrinsically and extrinsically generated ocular surface inflammation. The presence of delayed tear clearance may set up a vicious cycle to aggravate the existing inflammation. Future prospective studies are needed to delineate the pathogenic role of delayed tear clearance in various ocular surface disorders.

Corneal anesthetic abuse and Candida keratitis

PURPOSE

Topical corneal anesthetic abuse is a self-inflicted injury, causing profound corneal morbidity. Superimposed infection is an important complicating factor. The authors report four patients with confirmed topical anesthetic abuse of the cornea, in whom Candida keratitis developed.

METHODS

A retrospective review of the medical records of four patients with confirmed topical corneal anesthetic abuse and fungal keratitis.

RESULTS

A 21-year-old woman, two 28-year-old women, and a 35-year-old man were included in the study. All these patients sustained a corneal injury, prompting the chronic use of topical anesthetics (0.5% proparacaine hydrochloride in 3 patients, and 0.5% tetracaine hydrochloride and 0.4% benoxinate hydrochloride in the other). Corneal findings included epithelial defects in all patients, focal infiltrate in one patient, and ring-shaped stromal infiltrate in three patients. Topical anesthetic was discontinued, all patients initially were treated empirically with antibacterial agents, and three patients received topical corticosteroids. Subsequent corneal cultures grew Candida spp, Candida albicans specifically in three patients, and local and systemic antifungal therapy was started. Corneas in two patients re-epithelialized; a conjunctival flap was performed on another patient with a descemetocele; and the remaining patient was lost to follow-up, although repeat fungal cultures yielded no growth.

CONCLUSIONS

Corneal superinfection with Candida may occur during topical anesthetic abuse. Therapy includes discontinuation of the anesthetic and institution of antifungal therapy.

Touch sensitivity of the eyelid margin and palpebral conjunctiva

Using a slit-lamp biomicroscope mounted Cochet-Bonnet aesthesiometer, the touch sensitivity of the eyelid margin and palpebral conjunctiva was determined for both upper and lower lids in 30 subjects. Thresholds for the occlusal surface of the lid, the marginal angle and the middle of the tarsus were measured centrally. A significantly higher touch sensitivity was found for the marginal zone compared with the occlusal surface, and tarsal conjunctival sensitivity was substantially the lowest. The occlusal and marginal zones of the lower lid displayed a significantly higher touch sensitivity than the upper lid but the tarsal sensitivity of the two lids was similar. The sharp peaking of sensitivity at the leading edge of each eyelid provides a mechanism for the detection of superficial foreign bodies and presumably augments the protective role of the cornea. A large inter-subject variation in marginal touch sensitivity was found which may explain individual variation in contact lens adaptation.

Tear break-up time is related to blink frequency

The relationship between tear break-up time and blink frequency was investigated in a group of 41 subjects. A significant relationship between tear break-up time and blinking was found. This suggests that tear stability plays an important role in stimulating normal involuntary blinking.