Frequent spontaneous eyeblink activity associated with reduced conjunctival surface (trigeminal nerve) tactile sensitivity.

BACKGROUND: A number of recent studies have reported high spontaneous eyeblink rate (SEBR) values in apparently normal subjects, but the reasons for this are unclear. METHODS: An assessment was made of SEBR, in 60 educated adult male subjects aged between 22 and 40 years, over a period of 5 min in silence. Half of the subjects were classified as having frequent eyeblink activity. All subjects also had their corneal and conjunctival touch (tactile) sensitivity assessed with a Cochet-Bonnet aesthesiometer immediately after the video recording of SEBR. RESULTS: SEBR ranged from 4.6 to 43.5 (mean 18.6) eyeblinks/min. The SEBR was 26.8 +/- 6.0 eyeblinks/min for those with frequent eyeblink activity as compared to just 10.3 +/- 3.5 eyeblinks/min for those with normal eyeblink activity (p < 0.001). There was no difference in palpebral aperture or exposed ocular surface area between the two groups. The average central corneal sensitivity was only marginally different between the two groups (56.8 +/- 2.8 mm vs 58.5 +/- 2.3 mm) but the conjunctival threshold sensitivity was substantially different (at 23.8 +/- 4.3 mm vs 28.5 +/- 3.5 mm; p < 0.001). SEBR was inversely correlated with the conjunctival sensitivity in those with frequent eyeblink activity (p < 0.001). CONCLUSIONS: Our study provides a clue as to the mechanism of inhibition of spontaneous eyeblink activity, namely that a certain level of ocular surface (conjunctival) sensitivity is required to keep SEBR low.

Nucleus and cell size changes in human bulbar conjunctival cells after soft contact lens wear, as assessed by impression cytology.

PURPOSE: To specifically assess the nucleus size and its relationship to cell size for human bulbar conjunctival cells. METHODS: Impression cytology samples were taken from the nasal side of the intra-palpebral zone of the bulbar conjunctival surface from 20 young adult white European males, half of whom were successful daily soft contact lens wearers. A Millcell-CM filter was used, after topical anaesthesia with oxybuprocaine 0.4%, which was stained with Giemsa and colour images taken at 400x magnification by light microscopy. The images were graded and also a 35mm was prepared. From the projected image, an overlay method was used to outline the borders such that the cell and nucleus areas could be measured by planimetry. RESULTS: The group mean cell area values were 267+/-59microm(2) (n=10, +/-S.D.) and 1028+/-357microm(2) for the non-contact lens wearers and contact lens wearers, respectively. The cell nucleus areas were 64+/-11microm(2) and 99+/-19microm(2), respectively. Both the cell areas and nucleus area values were statistically different between the two groups (p<0.001). CONCLUSIONS: These studies confirm that soft contact lens wear can result in cell enlargement (squamous metaplasia) of the bulbar conjunctival cells. With this cell enlargement, the nucleus-to-cytoplasm ratio also changes, but the nucleus size generally increases (rather than decreases).

An assessment of the discomfort associated with the use of rose bengal 1% eyedrops on the normal human eye: a comparison with saline 0.9% and a topical ocular anaesthetic.

PURPOSE: To assess the time-dependent changes in ocular comfort following unilateral instillation of preservative-free rose bengal 1% eyedrops when compared with saline 0.9% or proxymetacaine 0.5%. METHODS: A total of 61 subjects, aged between 19 and 77 years, were asked to complete an ocular symptoms questionnaire, and then to indicate the comfort level for each eye on a 100-point visual analogue scale (VAS). A single drop of rose bengal was instilled in one eye (left or right) and a drop of saline or anaesthetic instilled in the other eye. The VAS assessments were repeated at an average of 4 and 7 min later. RESULTS: The instillation of rose bengal eyedrops produced an initial average reduction in comfort of 39.8 points, as compared with a reduction of 11.5 points following the anaesthetic and a reduction of 3.4 points for saline. However, the responses to rose bengal were highly variable, ranging from reductions of 1.5 to 84.6 points. In most subjects, some recovery had occurred within 6-8 min, but the comfort scores averaged 27.8 points below baseline levels prior to rose bengal. Slightly greater discomfort was noted by older subjects and those with darker irides. CONCLUSIONS: This study confirms that the use of rose bengal eyedrops can elicit a sensation of discomfort, but that this adverse reaction does not last very long. Based on the initial kinetics of recovery from discomfort, it is estimated that this should last no longer than 10-15 min (at least for those without significant ocular surface disease).

Further analysis of the human spontaneous eye blink rate by a cluster analysis-based approach to categorize individuals with 'normal' versus 'frequent' eye blink activity.

PURPOSE: To further analyze the possible causes of variability in spontaneous eye blink activity in apparently healthy humans. METHODS: One hundred men, aged between 23 and 57 years and with no significant eye disease, were questioned on the number of ocular symptoms they experienced (one, two, three, and so forth). Five-minute video recordings were made of the eyes in primary gaze and in silence between 11:00 and 17:00 hours. The spontaneous eye blink rate (SEBR) and palpebral aperture features were assessed from the video recordings. The central corneal threshold touch sensitivity was then assessed with a Cochet-Bonnet aesthesiometer. RESULTS: The average SEBR was 13.8 +/- 9.7 blinks per minute (range, 2.8-48 blinks per minute), but the distribution was heterogeneous and skewed to higher values. The SEBR was not obviously dependent on the time of day that the recordings were made, on the number of mild symptoms that the subjects reported, or on the central corneal sensitivity (P> or =0.6). Analysis of SEBR in relation to age showed a possible weak association (P=0.082, r = 0.175), but SEBR showed absolutely no correlation with palpebral aperture height (P=0.546). A hierarchic cluster analysis clearly resolved the distribution of SEBR values into two distinct groups (P<0.001, F ratio = 222). CONCLUSIONS: Spontaneous eye blink activity can be rather different between healthy individuals, even under a single experimental condition. These differences do not appear to be caused by the time of day, mild symptoms, corneal sensitivity, age, or palpebral aperture features. In line with previous metaanalyses, it is therefore proposed that individuals could be grouped as to whether they have "normal" eye blink activity or be classified as having "frequent" eye blink activity. The latter group would include those who had an SEBR greater than 20 blinks per minute when assessed in primary eye gaze and in silence.

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.

Use of a high molecular weight fluorescein (fluorexon) ophthalmic strip in assessments of tear film break-up time in contact lens wearers and non-contact lens wearers.

PURPOSE: To assess whether fluorexon strips could be used in tear stability [tear film break-up time (TBUT)] measures, as compared with fluorescein strips. METHODS: The pre-ocular tear film stability was assessed in 40 adults (19-29 years of age), half of whom were adapted soft contact lens wearers, using the dye-assisted tear film break-up time (TBUT) method. The measures were carried out between 10.00 and 17.00 hours, with contact lens wearers removing their lenses just before the assessments. For all subjects, fluorescein or fluorexon ophthalmic strips (pre-wetted with preservative-free saline) were used to add dye to the tear film, the TBUT was assessed three times and then the eye lightly irrigated with saline. The measures were repeated 45 min later with the other dye, with half the subjects receiving fluorescein first and the other half receiving fluorexon first. RESULTS: Overall, the mean TBUT times were 12.2 +/- 5.9 s for fluorescein and 12.6 +/- 5.6 s for fluorexon (p = n.s.), but the non-lens wearers had longer TBUT times (14.6 and 14.5 s for the two dyes) compared with contact lens wearers (9.8 and 10.7 s, p < 0.01). While the inter-subject variability (as S.D.) was larger for non-contact lens wearers, the intra-subject variability [as coefficient of variation (COV)] was greater in the contact lens wearers when fluorescein was used (p < 0.001). When analysed as a function of the time of day that the measures were made, there were clear trends for both the fluorescein and fluorexon. TBUT values to increase in non-contact lens wearers and decrease in contact lens wearers. These trends failed to reach statistical significance, but the results with the contact lens wearers showed less variation than the non-contact lens wearers. CONCLUSION: The use of a fluorexon dye-impregnated strip (pre-wetted with preservative-free saline) yielded comparable results with a fluorescein strip for assessments of tear film stability based on TBUT. The studies also indicate that further research is needed on changes in TBUT values during the day.

Visualisation of "Marx's line" along the marginal eyelid conjunctiva of human subjects with lissamine green dye.

PURPOSE: To qualitatively assess the frequency and intensity of the staining of Marx's line with lissamine green dye. METHODS: Eighty-five non-contact lens wearers, aged 18-78 years and of white (European) or Arabic origin, were assessed. The subjects had no major eye disease, although some had mild-to-moderate congestion of the main tarsal (Meibomian) glands and/or anterior blepharitis. Lissamine green dye strips were used to stain the marginal zone of the palpebral conjunctiva, and then high magnification photo slitlamp images were taken. RESULTS: A lissamine green staining line was unmistakable in 83 of the subjects, and just evident in the other two. The line extends along the entire length of the upper and lower lid margins, and the staining broadens and extends over the puncta. In most subjects, the lissamine green-stained line was posterior to the main tarsal gland orifices, but in five subjects it was distinctly anterior to the orifices. In over two-thirds of the subjects, the width of line was much less than the distance between the gland orifices, and was at a similar distance to its width from the orifices. However, in one-third of the subjects, the width of the line was around half that of the distance between the orifices or slightly greater (i.e. approximately 0.5 mm), and this feature was more commonly present in those of non-European origin. CONCLUSION: Lissamine green dye highlights a very distinct line of cells along the marginal zone, and should be a useful tool to visualise this feature. This line of cells is thought to be the natural site of contact between the eyelid margin and the surfaces of the bulbar conjunctiva and cornea.