Meibomian gland dysfunction (MGD) may be the underlying problem in chalazion, stye, blepharitis, evaporative dry eye syndrome and contact lens intolerance.
The pre-corneal tear film has three layers, a basal mucin layer produced by conjunctival goblet cells, a watery (aqueous) layer secreted by the lacrimal gland and a superficial thin lipid layer of meibomian oil replenished with each blink.
In the normal healthy eye, the force of each blink releases a minute quantity of meibomian oil onto the lid margins, lubricating the lid/lid and the lid/globe interactions. The tear film is refreshed with each blink as meibum also has a physiological 'screen wash' function.
In MGD, soreness, scratchiness, stickiness, tiredness and dry-feeling eyes can be attributed to impaired lid/globe lubrication, while burning and stinging may be attributable to altered lid margin water-wettability.
Grains of particulate matter from the lashes or lid margins may cause grittiness, transient foreign body sensation and irritation with paradoxical watering.
Blepharitis and dry eye syndrome are often associated with concomitant MGD.
Eye specialists make the definitive diagnosis of MGD using slit lamp examination but characteristic symptoms of dry eye and blepharitis suggest the diagnosis of MGD on symptom history alone (see box).
There is considerable clinical and symptomatic overlap between evaporative dry eye, blepharitis and contact lens intolerance.
Dry eye syndromes occur because of a poor lipid layer or a poor aqueous layer in the pre-corneal tear film. The term 'evaporative dry eye' describes the situation when the poor quantity and quality meibomian secretions result in a feeble pre-corneal lipid layer and rapid evaporation of the aqueous tear layer. Tear evaporation rates are significantly higher than normal in patients with MGD because of the unstable tear film.
|Examination and Signs|
|A simple hand-held magnifying glass may help.
Ocular lubricants have been the mainstay of dry eye treatments for many years. GPs and rheumatologists often use hypromellose drops as first-line therapy for such patients.
As MGD is the major contributory factor in evaporative dry eye, regular use of an effective warm compress once or twice daily can help.
In MGD, the meibomian gland secretion meibum solidifies because of chemical changes in the lipid composition.
The melting point of meibum is elevated to 39 degsC in MGD while normal eyelids are 33.5 degsC. Effective warm compresses deliver a sustained elevation in eyelid temperature, which drops the viscosity of the secretions resulting in better function of the pre-corneal tear film.
Patient information leaflets for blepharitis and MGD recommend patients use a hot wet flannel to provide the warm compress. As hot wet flannels are a hassle to use, most patients simply do not do it well enough or often enough to benefit.
I saw so many patients returning to my eye clinics with poorly treated MGD that I designed a re-usable hot compress that stays warm for about 10 minutes (the EyeBag), significantly improving patient compliance.
In severe MGD, a three-month course of doxycycline 100mg once daily is often useful. Erythromycin 250mg twice daily for three months is the second-line treatment.
Lid wipes, weak solutions of baby shampoo, bicarbonate of soda and physically scrubbing the lid margins with cotton buds have all been recommended at various times but these measures have not been subject to rigorous controlled trials.
Oral omega-6 essential fatty acids may be of benefit in MGD, in conjunction with lid hygiene.
- Mr James is consultant ophthalmologist at Calderdale Royal Hospital, Halifax
- Mr James designed and has financial interest in the MGDRx EyeBag (www.eyebag.co.uk)