Sir,

I read with interest the article by Isreb et al,1 where they have positively correlated the lipid layer thickness with fluorescein tear film break-up time (FBUT) and Schirmer's test (STA).

Meibomian gland dysfunction (MGD) is a fairly common condition, and the reported prevalence at one study was 38.9%.2 It is easy to guess therefore that it is one of the major causes of dry eye syndrome. It is therefore quite a useful study, and I would like to convey my appreciation to all the authors.

Meibum (Meibomian gland secretion) contains hydrocarbons, sterol esters, wax esters, triglycerols, free cholesterols, free fatty acids, and polar lipids (in decreasing order of abundance). Meibum melts at 35°C and is thus liquid at the surface of the eye.3 This property of the lipid layer is utilized in the treatment of dry eyes using hot compresses.4

The normal lipid layer thickness is stated to be ideally more than 120 nm, however, will a thickness of less than 60 nm alone with normal FBUT and STA be sufficient for a diagnosis of dry eye.2

Tandem scanning confocal microscopy is another modality for the assessment of the tear film and is thought to be more accurate than the method used by the authors. It would be nice to know the authors' opinion on this.