E. Ian Pearce

The International Workshop on Meibomian Gland Dysfunction: Report of the Diagnosis Subcommittee

Diagnostic tests of meibomian gland dysfunction (MGD) and of MGD-related disorders are based on the demonstration of abnormal anatomy and physiology of the glands and the detection of specific pathologic events. For this reason, this subcommittee report is divided into two sections. In part I, those aspects of meibomian anatomy and physiology that are relevant to currently available tests are described; a fuller account of the anatomy and physiology is provided in the report of the Anatomy Subcommittee of this workshop. In part II, each test and its performance is described in detail. In part III, the practical application of selected tests is summarized and recommendations for future approaches are made. Additional recommendations and a summary of pertinent literature and concepts are presented in Appendices 1 to 17.

What does the phenol red thread test actually measure

Purpose. This study attempts to resolve whether the phenol red thread test (PRT) is a test of tear volume or tear production through comparisons with other techniques. Methods. Twenty asymptomatic subjects (10 men and 10 women; average age 30.6 ± 10.8 years) had PRT (Zone Quick, Menicon) results compared with tear turnover rate (by fluorophotometry; Fluorotron Master, OcuMetrics) and tear volumes (from tear meniscus height and back extrapolation from fluorometric data). Results. PRT wetting was not correlated with either tear turnover or volume (by fluorophotometry or tear meniscus height) on a Pearson product moment correlation test (p > 0.05). Conclusions. No clear experimental evidence in favor of the PRT being a measure of tear production or volume was found. It is probable that the PRT measures uptake of a (small) amount of fluid residing in the eye, stimulates a low degree of reflex tearing, and reflects the absorption characteristics of the thread dependent on the biophysics or composition of tears.

EFFECT OF ORAL CONTRACEPTIVES ON TEAR PHYSIOLOGY

Variations in sex hormones due to the menstrual cycle (and oral contraceptives) were evaluated for their effect on tear physiology. Subjects were 18 females taking oral contraceptives or their age matched controls (no medication), aged 21–33 years. Symptoms of ocular discomfort (visual analog scale), tear film structure (TearScope), non‐invasive tear thinning time (HirCal grid), evaporation rate (ServoMed evaporimeter), osmolality (Nanolitre Osmometer), tear turnover rate, tear volume (Fluorotron Master), and tear protein levels (HPLC) were measured around day 2 (D2), actually day 1–4 and day 19 (D19) actually day 18–21 of the cycle. No significant differences were found for any tear parameters between D2 and D19 for either pill users or controls alone, or in the comparison of pill users with controls. No effect on tear physiology was found for serum hormone changes induced by oral contraceptive use or by normal cyclic variations in healthy young females.

Spatial location studies on the chemical composition of human tear ferns.

Tear ferns are the patterns formed when tears are allowed to dry on a clean smooth surface. The patterns have been categorised according to confluence of pattern,with less confluent ferns indicative of tear film abnormalities. Little is known about the mechanism that gives rise to this phenomenon. Previous work has concentrated on correlation of alterations in tear film composition on the ferning phenomenon. The present study takes a new approach by analysing the locations of chemical elements in the fern to understand how the ferns form. By means of SEM coupled with EDXA, Na, K and Cl were detected within the fern. Sulphur, indicative of the presence of macromolecules such as mucins and proteins, was only found at the very periphery of the dry tear drop. The results suggest that macromolecules do not play a direct role in the formation of the ferns. A model is put forward to explain the observation whereby proteins and mucins are precipitated selectively by increasing salt concentration at the drop margin.

An improved fluorophotometric method for tear turnover assessment.

Purpose Scanning fluorophotometry is considered the “gold standard” to determine tear turnover rates (TTR). In this study, we attempted to improve the precision of basal TTR by fluorophotometry through a number of methodological changes. Methods By means of a timer program that produces audio cues, a new methodology that ensures confluence and a constant thickness of the tear film and minimization of reflex lacrimation as a result of the inhibition of the blink reflex was developed. This was compared with the standard protocol, both in a paired study and by a review of unpaired data. The minimum length of time required to monitor TTR measurements was also investigated. Results A significant improvement in correlation coefficient (r) of the log decay curve was observed as a result of changes in the protocol in both the paired (p = 0.016) and unpaired study (p < 0.0001). We determined that it was sufficient to monitor TTR for 10 min to obtain accurate results. Conclusions We advocate that the changes be adopted as widely as possible for the precise and rapid measurement of basal tear turnover rates.

Effect of an Oil and Water Emulsion on Tear Evaporation Rate

Dry eye patients have been divided primarily into two categories, evaporative or tear production-deficient.1 In both cases, increased tear evaporation and by extension, evaporation rate, is a significant parameter in the etiology and pathogenesis of dry eye. Paradoxically, the use of tear supplements has been shown to exacerbate tear evaporative loss.2 Theoretically, tear supplements should cause minimal increases in evaporation and ideally, should reduce evaporation of the tear film.

Does the niqab (veil) wearer satisfy the minimal visual field for driving

Visual field testing of subjects wearing a niqab was carried out using the approved (Esterman) test on a Humphrey perimeter to determine if visually normal subjects met the European driving standard. Measurement of aperture dimensions of the niqab when worn was recorded. When wearing the niqab, all subjects achieved a visual field adequate to satisfy UK/European driving standards. A measurement of the limiting aperture size was obtained and a self‐test method for niqab wearers was determined.

The Influence of Automobile Windscreen Rake on Effective Light Transmittance

The theoretical transmittances at the installation angle of the windscreens of the ten best‐selling cars in the UK in 2008 are investigated. The data show that the ten most popular cars on the UK roads have a windscreen rake that reduces transmittance to a value close to or below that specified in International Standards for normal incidence. British and International Standards for windscreen transmittance should be revisited by the relevant authorities in the light of the high rake angles that have become widespread in recent years. The problem is worsened considerably by tinted windscreens having become the default option in many models. It is also suggested that there may be good reason for all spectacles supplied to drivers for low light level driving to be untinted and anti‐reflection coated.

Is the spectacle lens jack‐in‐the‐box phenomenon really due to the lenses?

The calculation of the extent of the ring scotoma around positive lenses, as conventionally taught to students of clinical optics, indicates that the scotoma is of a significant size. Using knife‐edge lenses this study shows that the calculations are invalid due to the finite size of the eyes entrance pupil and in many instances the scotoma is shown not to exist. The effect noticed in clinical practice is probably largely due to the frame and the edging techniques used which add to the refractive scotoma which is present with high powered lenses, large apertures and/or small pupil sizes.

Tear Protein Levels Following Punctal Plugging

Occlusion of the lacrimal drainage system has been advocated in cases of dry eye where other forms of treatment including artificial tears and lid hygiene have proved inadequate. The first method of occlusion suggested was cautery of the tissue around the canaliculus and punctum to prevent tear drainage.1 The first temporary occlusion technique was described in the city of Glasgow by Foulds2 in 1961 who advocated the use of gelatin implants. Today collagen plugs are commercially available (Eagle Vision, Memphis, TN; Lacrimedics, Rialto, CA) to temporarily block tear drainage. The efficacy of dissolvable collagen in blocking punctal drainage is less than complete.3–5 Lowther and Semes5 found that collagen plugs had no appreciable effect on tear break-up, tear prism height, fluorescein, or rose bengal staining, yet patients reported that dryness-related symptoms were significantly reduced.