How to use a slit lamp
Slit lamp examination is the most important part to detect any abnormality or disease during eye examination. The steps of slit-lamp examination are
- Patient should be positioned comfortably with his chin resting on chin rest and forehead opposed to head rest.
- The height of the table housing the slit lamp should be adjusted according to patient’s height.
- The microscope and illumination system should be aligned with the patient’s eye to be examined.
- Focus the microscope by
- Adjusting the interpupillary distance
- Adjusting the eyepieces (set at 0 or dial in your refraction)
- Set magnification in on 1x
- Move the microscope up and down, in or out or latterly byjoystickso that the tissue that is of interest comes clearly into view.
- Adjust the illumination or brightness through the desired filters.
- Adjust the width and height of the beam.
Start systematic examination of eye from front to the back as follow :
1. Eye lid margin
Slit lamp beam is widened to a full circle to illuminate the front of eye. The anterior border shows the eyelashes projecting in two or three rows and its posterior border is sharp and resting against theeyeball. There are small orifices of the tarsal glands just in front of the lid margin and the lacrimal papilla.
- Palpebral:This structure is seenby everting the eyelids, it is a thin, transparent mucous membrane lining the inner surface of the eyelid.
- Bulbar:This structure is examined by holding the lids open and asking the patient to look to the right, left, up, and down. Here again the conjunctiva is seen as a thin, transparent mucous membrane. A superficial, bright red system of anastomosing vessels can be easily identified in the bulbar conjunctiva.
It is the transparent layer. When the slit-lamp beam passes through the cornea, it is possible to recognize the anterior and posterior surfaces and the corneal stroma.
sclera is the white part of eye.
5. Anterior chamber:
Normally the anterior chamber filled with aqueous appears optically empty and black. If the slit beam is narrowed to a fine pencil of light, a very faint relicense can be made out along the course of the light. Angle of anterior chamber is assessed by gonioscopy.
6 .Iris and pupil:
Iris is the colored part of eye. In the centre there is an opening known as pupil. It controls the amount of light going into the eye by the constriction and dilation of pupil.
Check whether the lens is transparent or cloudy (cataract).
8. Vitreous body
Itis just posterior to the lens. In the vitreous of aged patients, other condensations can be seen; these are thought to represent areas of degeneration.
Other usage of slit lamp with accessory devices
1. Fundus examination:
Fundus examination can be performed by placing an additional handheld 78D or 90D lens in front of the eye. Normally the fundus has a red appearance, the optic disc is pink, round or oval shaped with sharp margins. Macula is situated 3 mm temporally to the optic disc. It is small circular area, deeper red than the surrounding fundus, there is a bright foveal reflex in the Centre. The normal artery: vein ratio in fundus is 2:3.
2. Applanation tonometry:
The IOP can be measured on slit lamp with the help of Goldman applanation tonometer. An applanation tonometer measures the IOP by flattening the cornea overa specific area (3.06mm).
Anaesthetize the cornea and stain the tear film with fluorescein. Patient is seated in front of a slit lamp and the cornea and biprisms are illuminated with cobalt blue light from the slit-lamp. Biprism is then advanced until it just touches the apex of cornea. At this point two fluorescent semicircles are viewed through the prisms. The applanation force against the cornea is adjusted until the inner edges of the two semicircles just touch. The IOP is determined by multiplying the dial reading with 10.
The angle of the anterior chamber of the eye cannot be seen by direct inspection because of the light rays arising from the angleundergo total internal reflection on reaching the curved surface of the cornea. The use of a special contact lens, a source of focal illumination, and a microscope or slit lamp makes the angle accessible. The contact lens eliminates the corneal curve and allows light to be reflected from the angle.
Slit lamp photography
Slit-lamp photography can be done by attaching the smartphones to slit-lamp by using slit lamp adaptors. a slit lamp adaptor has two parts, one part holds the smartphone, whereas the other part fixes onto the eyepiece of the slit lamp. There are different types of slit-lamp adaptors according to the eyepiece of the slit-lamp:
- 10x eyepiece adaptors
- 12x eyepiece adaptors