Touch sensitivity of the eyelid margin and palpebral conjunctiva

A Hue-Value method for semi-automated assessment of Lid Wiper Epitheliopathy

BACKGROUND

Lid wiper epitheliopathy (LWE) is a marker of an abnormal lid/cornea interaction. This study proposes an automated Hue-Value grading algorithm of LWE staining following manual selection of the region of interest.

METHODS

Images of LWE staining were processed using Hue and Value from HSV (Hue-Saturation-Value) color space with a custom MATLAB program. Thirty-one images were successfully analyzed. Examiners analyzed images in random order twice, separated by more than a week. Bland Altman and Intraclass Correlation Coefficients (ICC) were performed.

RESULTS

There was no difference (p > 0.05) between upper (UL) and lower (LL) eyelids for LWE height (UL: 0.12 ± 0.12 mm, LL: 0.12 ± 0.07 mm), width (UL: 10.70 ± 3.84 mm, LL: 10.26 ± 3.49 mm), or area (UL: 2.85 ± 2.67 mm2, LL: 2.63 ± 1.71 mm2). There was no between examiner difference for all eyelid LWE height or area (p > 0.05), but a difference in LWE width (0.16 mm; p = 0.031). ICC for LWE height, width and area were 0.996 (95% CI: 0.993 to 0.998), 0.997 (95% CI: 0.992 to 0.998) and 0.999 (95% CI: 0.998 to 0.999). There was no between examiner difference for height or area (p > 0.05) for UL, but a difference in LWE width (0.28 mm; p = 0.026). ICC for height, width and area were 0.999 (95% CI: 0.996 to 1.00), 0.995 (95% CI: 0.982 to 0.999) and 1.00 (95% CI: 0.999 to 1.00). There was no difference in LWE height, width or area for LL (all p > 0.05). ICC were 0.991 (95% CI: 0.973 to 0.997) for height, 0.998 (95% CI: 0.995 to 0.999) for width and 0.997 (95% CI: 0.990 to 0.999) for area.

CONCLUSIONS

This novel method results in highly repeatable interexaminer measures of LWE staining after general lid region delineation. Small differences in LWE width were observed between examiners.

CLEAR - Anatomy and physiology of the anterior eye

A key element of contact lens practice involves clinical evaluation of anterior eye health, including the cornea and limbus, conjunctiva and sclera, eyelids and eyelashes, lacrimal system and tear film. This report reviews the fundamental anatomy and physiology of these structures, including the vascular supply, venous drainage, lymphatic drainage, sensory innervation, physiology and function. This is the foundation for considering the potential interactions with, and effects of, contact lens wear on the anterior eye. This information is not consistently published as academic research and this report provides a synthesis from all available sources. With respect to terminology, the report aims to promote the consistent use of nomenclature in the field, and generally adopts anatomical terms recommended by the Federative Committee for Anatomical Terminology. Techniques for the examination of the ocular surface are also discussed.

CLEAR - Effect of contact lens materials and designs on the anatomy and physiology of the eye

This paper outlines changes to the ocular surface caused by contact lenses and their degree of clinical significance. Substantial research and development to improve oxygen permeability of rigid and soft contact lenses has meant that in many countries the issues caused by hypoxia to the ocular surface have largely been negated. The ability of contact lenses to change the axial growth characteristics of the globe is being utilised to help reduce the myopia pandemic and several studies and meta-analyses have shown that wearing orthokeratology lenses or soft multifocal contact lenses can reduce axial length growth (and hence myopia). However, effects on blinking, ptosis, the function of Meibomian glands, fluorescein and lissamine green staining of the conjunctiva and cornea, production of lid-parallel conjunctival folds and lid wiper epitheliopathy have received less research attention. Contact lens wear produces a subclinical inflammatory response manifested by increases in the number of dendritiform cells in the conjunctiva, cornea and limbus. Papillary conjunctivitis is also a complication of all types of contact lenses. Changes to wear schedule (daily disposable from overnight wear) or lens materials (hydrogel from SiHy) can reduce papillary conjunctivitis, but the effect of such changes on dendritic cell migration needs further study. These changes may be associated with decreased comfort but confirmatory studies are needed. Contact lenses can affect the sensitivity of the ocular surface to mechanical stimulation, but whether these changes affect comfort requires further investigation. In conclusion, there have been changes to lens materials, design and wear schedules over the past 20+ years that have improved their safety and seen the development of lenses that can reduce the myopia development. However, several changes to the ocular surface still occur and warrant further research effort in order to optimise the lens wearing experience.

Anatomical and physiological considerations in scleral lens wear: Conjunctiva and sclera

While scleral lenses have been fitted using diagnostic lenses or impression moulding techniques for over a century, recent advances in anterior segment imaging such as optical coherence tomography and corneo-scleral profilometry have significantly improved the current understanding of the anatomy of the anterior eye including the morphometry of the conjunctiva, sclera, and corneo-scleral junction, as well as the ocular surface shape and elevation. These technological advances in ocular imaging along with continual improvements and innovations in scleral lens design and manufacturing have led to a global increase in scleral lens prescribing. This review provides a comprehensive overview of the conjunctiva and sclera in the context of modern scleral lens practice, including anatomical variations in healthy and diseased eyes, the physiological impact of scleral lens wear, potential fitting challenges, and current approaches to lens modifications in order to minimise lens-induced complications and adverse ocular effects. Specific topics requiring further research are also discussed.

TFOS DEWS II pain and sensation report

Pain associated with mechanical, chemical, and thermal heat stimulation of the ocular surface is mediated by trigeminal ganglion neurons, while cold thermoreceptors detect wetness and reflexly maintain basal tear production and blinking rate. These neurons project into two regions of the trigeminal brain stem nuclear complex: ViVc, activated by changes in the moisture of the ocular surface and VcC1, mediating sensory-discriminative aspects of ocular pain and reflex blinking. ViVc ocular neurons project to brain regions that control lacrimation and spontaneous blinking and to the sensory thalamus. Secretion of the main lacrimal gland is regulated dominantly by autonomic parasympathetic nerves, reflexly activated by eye surface sensory nerves. These also evoke goblet cell secretion through unidentified efferent fibers. Neural pathways involved in the regulation of meibomian gland secretion or mucin release have not been identified. In dry eye disease, reduced tear secretion leads to inflammation and peripheral nerve damage. Inflammation causes sensitization of polymodal and mechano-nociceptor nerve endings and an abnormal increase in cold thermoreceptor activity, altogether evoking dryness sensations and pain. Long-term inflammation and nerve injury alter gene expression of ion channels and receptors at terminals and cell bodies of trigeminal ganglion and brainstem neurons, changing their excitability, connectivity and impulse firing. Perpetuation of molecular, structural and functional disturbances in ocular sensory pathways ultimately leads to dysestesias and neuropathic pain referred to the eye surface. Pain can be assessed with a variety of questionaires while the status of corneal nerves is evaluated with esthesiometry and with in vivo confocal microscopy.

TFOS DEWS II pathophysiology report

The TFOS DEWS II Pathophysiology Subcommittee reviewed the mechanisms involved in the initiation and perpetuation of dry eye disease. Its central mechanism is evaporative water loss leading to hyperosmolar tissue damage. Research in human disease and in animal models has shown that this, either directly or by inducing inflammation, causes a loss of both epithelial and goblet cells. The consequent decrease in surface wettability leads to early tear film breakup and amplifies hyperosmolarity via a Vicious Circle. Pain in dry eye is caused by tear hyperosmolarity, loss of lubrication, inflammatory mediators and neurosensory factors, while visual symptoms arise from tear and ocular surface irregularity. Increased friction targets damage to the lids and ocular surface, resulting in characteristic punctate epithelial keratitis, superior limbic keratoconjunctivitis, filamentary keratitis, lid parallel conjunctival folds, and lid wiper epitheliopathy. Hybrid dry eye disease, with features of both aqueous deficiency and increased evaporation, is common and efforts should be made to determine the relative contribution of each form to the total picture. To this end, practical methods are needed to measure tear evaporation in the clinic, and similarly, methods are needed to measure osmolarity at the tissue level across the ocular surface, to better determine the severity of dry eye. Areas for future research include the role of genetic mechanisms in non-Sjögren syndrome dry eye, the targeting of the terminal duct in meibomian gland disease and the influence of gaze dynamics and the closed eye state on tear stability and ocular surface inflammation.

Lid Wiper Microvascular Responses as an Indicator of Contact Lens Discomfort

PURPOSE

To analyze quantitatively the alterations in the microvascular network of the upper tarsal conjunctiva, lid wiper, and bulbar conjunctiva relative to ocular discomfort after contact lens wear.

DESIGN

A prospective, crossover clinical study.

METHODS

Functional slit-lamp biomicroscopy was used to image the microvascular network of the upper tarsal conjunctiva, lid wiper, and bulbar conjunctiva. The microvascular network was automatically segmented, and fractal analyses were performed to yield the fractal dimension (D_box) that represented vessel density. Sixteen healthy subjects (9 female and 7 male) with an average age of 35.5 ± 6.7 years (mean ± standard deviation) were recruited. The right eye was imaged at 9 AM and 3 PM at the first visit (day 1) when the subject was not wearing contact lenses. During the second visit (day 2), the right eye was fitted with a contact lens for 6 hours. Microvascular imaging was performed before (at 9 AM) and after lens wear (at 3 PM). Ocular comfort was rated using a 50-point visual analog scale before and after 6 hours of lens wear, and its relationships with microvascular parameters were analyzed.

RESULTS

There were no significant differences in D_box among the upper tarsal conjunctiva, lid wiper, and bulbar conjunctiva among the measurements at 9 AM (day 1 and day 2) and 3 PM (day 1) when the subjects were not wearing the lenses (P > .05), whereas after 6 hours of lens wear, the microvascular network densities were increased in all 3 of these locations. D_box of the lid wiper increased from 1.411 ± 0.116 to 1.548 ± 0.079 after 6 hours of contact lens wear (P < .01). D_box of the tarsal conjunctiva was 1.731 ± 0.026 at baseline and increased to 1.740 ± 0.030 (P < .05). D_box of the bulbar conjunctiva increased from 1.587 ± 0.059 to 1.632 ± 0.060 (P < .001). The decrease in ocular discomfort was strongly related to the D_box change in the lid wiper (r = 0.61, P < .05). There were no correlations between the changes of ocular comfort and the microvascular network densities of either the tarsal or bulbar conjunctivas (P > .05).

CONCLUSIONS

This study is the first to show that the microvascular network of the lid wiper can be quantitatively analyzed in contact lens wearers. The microvascular responses of the lid wiper were significantly correlated with contact lens discomfort.

Lid wiper epitheliopathy

Some recent research has resulted in a hypothesis that there is a common 'lid wiper' region that is apposite to the ocular surface or anterior lens surface (where contact lenses are worn), responsible for spreading tears during blinking. In the upper eyelid, it extends about 0.6 mm from the crest of the sharp posterior (inner) lid border (i.e. the mucocutaneous junction, or line of Marx) to the subtarsal fold superiorly and from the medial upper punctum to the lateral canthus horizontally. Histologically, it is seen as an epithelial elevation comprising of stratified epithelium with a transitional conjunctival structure of (moving posteriorly) squamous cells then cuboidal cells, with some parakeratinised cells and goblet cells. Lid wiper epitheliopathy (LWE) denotes staining of the lid wiper observed after instillation of dyes such as fluorescein, rose bengal or lissamine green. There have been some reports of higher rates of LWE in dry eye patients and contact lens wearers, but others have failed to find such associations. The primary cause of LWE is thought to be increased friction between the lid wiper and ocular or anterior contact lens surface due to inadequate lubrication, which could be caused by dry eye and may be exacerbated by factors such as abnormal blinking patterns, poor contact lens surface lubricity and adverse environmental influences. Recent evidence suggests that LWE is associated with sub-clinical inflammation. LWE has the potential to provide the missing mechanistic link between clinical observation and symptoms associated with dry eye and contact lens wear. Clinical and fundamental research into LWE is still in its infancy and in many instances equivocal; however, it is an idea that provides a potentially important new avenue for further investigation of anterior eye discomfort associated with ocular dryness and contact lens wear.

The neurobiology of the meibomian glands

This article compiles research regarding the neuroanatomy of the meibomian glands and their associated blood vessels. After a review of meibomian gland morphology and regulation via hormones, a case for innervation is made based on anatomical findings whereby the nerves lack a myelin sheath and Schwann cells. The localization and co-localization of dopamine beta-hydroxylase, tyrosine hydroxylase, neuropeptide Y, vasoactive intestinal polypeptide, calcitonin gene-related peptide, and substance P are explored with emphasis on differences that exist between species. The presence of the various neuropeptides/neurotransmitters adjacent to the meibomian gland versus the vasculature associated with the meibomian gland is documented so that conclusions can be made with regard to direct and indirect effects. Research regarding the presence of receptors and receptor proteins for these neuropeptides is documented. Evidence supporting the influence of certain neurotransmitters and/or neuropeptides on the meibomian gland is given based on research that correlates changes in meibomian gland morphology and/or tear film with changes in neurotransmitter and/or neuropeptide presence. Conclusions are drawn related to direct and indirect regulation and differences between the various nervous systems.

The relation between blinking and conjunctival folds and dry eye symptoms

PURPOSE

To investigate the relationship between blink action, dry eye symptoms, and lid-parallel conjunctival folds (LIPCOF).

METHODS

In 30 subjects (14 were women; mean [standard deviation {SD}] age, 42.4 [±12.3] years), spontaneous blinks were recorded from a temporal-inferior view (high-speed video), and the blink extent (incomplete [IC], almost complete [AC], and complete [CC]) was evaluated. Dry eye symptoms were evaluated using the Ocular Surface Disease Index (OSDI), and nasal and temporal LIPCOF grades were noted. Correlations between groups were calculated with Pearson correlation (or Spearman rank in nonparametric data), and differences between groups were calculated with an unpaired t-test (or U-test Mann-Whitney in nonparametric data).

RESULTS

Blink rate was significantly higher in females (22.0% [±16.8]) than in males (8.6% [±7.2]; unpaired t-test: p = 0.007). The percentage of AC of all blinks (AC%) was significantly correlated to LIPCOF sum (nasal + temporal) and OSDI scores (r > 0.570, p < 0.001). The percentage of IC was significantly correlated to LIPCOF sum (r = -0.541, p < 0.001) but not to OSDI.

CONCLUSIONS

The frequency and type of blinking may have an effect on dry eye symptoms and LIPCOF severity since almost all complete blinks were significantly related to both factors.

The TFOS International Workshop on Contact Lens Discomfort: report of the subcommittee on neurobiology

This report characterizes the neurobiology of the ocular surface and highlights relevant mechanisms that may underpin contact lens-related discomfort. While there is limited evidence for the mechanisms involved in contact lens-related discomfort, neurobiological mechanisms in dry eye disease, the inflammatory pathway, the effect of hyperosmolarity on ocular surface nociceptors, and subsequent sensory processing of ocular pain and discomfort have been at least partly elucidated and are presented herein to provide insight in this new arena. The stimulus to the ocular surface from a contact lens is likely to be complex and multifactorial, including components of osmolarity, solution effects, desiccation, thermal effects, inflammation, friction, and mechanical stimulation. Sensory input will arise from stimulation of the lid margin, palpebral and bulbar conjunctiva, and the cornea.

Eyelid sensation after supratarsal lid crease incision

PURPOSE

To determine the severity and duration of the loss of eyelid sensation after upper eyelid crease incision.

METHODS

This clinic-based case study was performed by analyzing observational measurements of patients undergoing upper blepharoplasty or ptosis surgery. Eighty-three eyelids of 50 patients were studied. A Cochet-Bonnet filament-type aesthesiometer was used to obtain all measurements. Preoperative and postoperative measurements were recorded at 1 week, 1 month, and final (2-6 months) time periods. Statistical analysis evaluated the degree and duration of the sensory loss and the extent of recovery during the evaluation period. Recovery of sensation was defined as a numerical reading within one point of baseline.

RESULTS

The mean aesthesiometry reading was calculated at the preoperative (3.45), 1-week (1.20), 1-month (1.56), and final postoperative (2.56) periods. Paired t testing showed a decreased but significant difference in sensation measurement at each comparison. Recovery of sensation to within one point occurs at the preoperative to late time period comparison. All but 4 of the 68 eyelids tested at the 1-week postoperative time period had a measured loss of sensation. Of the 44 eyelids tested at the final time period, all but 1 had regained some or all of this sensory loss.

CONCLUSIONS

Loss of skin sensation in the eyelid after upper eyelid crease incision blepharoplasty or blepharoptosis repair occurs in most patients and should be considered an expected outcome of the procedure. Partial to complete recovery of eyelid sensation over 2 to 6 months should also be expected, though in rare instances this does not occur.

The effect of long-term, daily contact lens wear on corneal sensitivity

PURPOSE

To assess the effect of long-term, daily-wear soft contact lenses and rigid gas permeable (RGP) contact lenses on corneal sensitivity using a noninvasive, air-pulse stimulus.

METHODS

The central and peripheral (temporal, medial, inferior) corneal sensation thresholds of 40 non-lens wearers, 40 soft lens wearers, and 40 RGP lens wearers were assessed using the Non-Contact Corneal Aesthesiometer (NCCA). The individuals who wore contact lenses were grouped according to the number of years of lens wear (10 years or less, 11-20 years, and 21 years or more).

RESULTS

Although a significant reduction in corneal sensitivity was found between the contact lens wearers and non-lens wearers (p = 0.000), no difference was found between the two lens-type subgroups (p = 0.939). This pattern of significance was repeated at each of the peripheral test locations. No relationship between corneal sensitivity and years of lens wear was found centrally (r2 = 0.004) or at any of the peripheral test locations. No significant difference was found between the central corneal sensation thresholds for the different subgroups of lens wear duration (p = 0.469) or for any of the peripheral test locations.

CONCLUSIONS

Both soft and RGP lens wear produce a similar type of corneal sensitivity loss, although the mechanism for this loss is different for the two lens types. The extent of sensitivity loss is not related to the duration of lens wear and appears to plateau after the first few months of wear. No topographical variation in sensitivity loss was found with lens type or with the duration of lens wear.