1 Use infrared light to uncover hidden treasures
If you are lucky enough to have a background illuminating system, employ infrared light to visualise the meibomian glands to aid in a dry eye workup. Meibomian gland dysfunction (MGD) is thought to be the leading cause of evaporative dry eye, a condition which accounts for up to 80 per cent of dry eye cases.1
The International Workshop on Meibomian Gland Dysfunction defined MGD as ‘a chronic, diffuse abnormality of the meibomian glands, commonly characterised by terminal duct obstruction and/or qualitative/quantitative changes in the granular secretion’.2 Infrared meibography allows non-invasive, in-vivo assessment of the structure of the meibomian glands.
With significant correlations found between the area of loss of meibomian glands and lipid layer thickness, non-invasive break up time, and dry eye symptoms, assessment of the meibomian glands should form an integral part of any dry eye assessment.
To capture infrared images, turn off all the white light, turn on the infrared light and use x10 – x16 magnification to focus on the everted lid. Image A (left) shows healthy glands, while B shows central glad drop out in MGD.
A recent study has shown that application of a warm compress and massage can help improve and even reverse meibomian gland drop out.3
2 Capturing a corneal section
When capturing an image of a corneal section (A), to give the image some perspective use a small amount of background illumination (B).
As an optical section beam width is so narrow, play around with the ISO settings and shutter speeds to maximise light capture. Although increasing the ISO will increase the sensitivity of the camera to light, creating a brighter slit, it will also increase the noise in the photo.
Decreasing the shutter speed will also increase the amount of light captured; however, this relies upon the subject keeping particularly still to obtain a crisp image.
3 Utilise the principles of internal reflection
Sclerotic scatter is an indirect illumination technique which relies upon total internal reflection of light through the cornea.
The soft, indirect light used in this technique is useful for imaging subtle corneal pathologies, including vortex dystrophy and corneal scarring. To perform this technique, focus your slit lamp on the cornea using 10x illumination, then uncouple the illumination from the magnification system and project the illumination to the limbus.
Move right and left until a bright ring is seen around the edge of the cornea. Where no pathology exists all light will be internally reflected and the cornea will appear dark. If pathology is present, this will disrupt the internal reflection and scatter light forward, therefore appearing bright against a relatively dark background.
No background illumination should be used for this technique and the consulting room should be as dark as possible.
Read more
Part 1: Top tips for slit-lamp imaging
Part 3: Top tips for slit-lamp imaging
References
1 Castillanos E, Torres J, Fernandesz I, Martinez-Osorio H, Herreras JM, et al. Preponderance of evaporative over aqueous deficient-type dry eye syndrome in patients with chronic dry eye-related symptoms. Invest Ophthalmol Vis Sci 2008;49:E-Abstract 2371.
2 Tomlinson A, Bron AJ, Korb DR, Amano S, et al. The international workshop on meibomian gland dysfunction: report of the diagnosis subcommittee. Invest Ophthalmol Vis Sci 2011;52:2006Y49.
3 Bilkhu PS, Naroo SA, Wolffsohn JS. Randomised masked clinical trial of the MGDRx EyeBag for the treatment of Meibomian gland dysfunction-related evaporative dry eye. Br J Ophthalmol 2014; 98 (12): 1707-11.
Dr Rachel Hiscox is clinical affairs specialist for Topcon GB