Slit lamp Flashcards
Slit lamp use
The slit lamp allows a three-dimensional view of the anterior segment of the eye and, with the additional use of handheld lenses, binocular fundoscopy.
Videos on full assessment
https://jnjvisionpro.co.uk/education-centre/resource-library/slit-lamp-technique-videos
Mechanism
A slit lamp biomicroscope is a powerful tool for examining the eye. The illumination beam can be focused into a very thin ‘slit’, which allows the determination of the depth and size of any abnormalities.
Components of slit lamp
Illumination arm and viewing arm - both arms of the slit lamp rest on a base. Under the base is the switch to turn the slit lamp on.
The base has a height-adjustable table with its own switch and buttons
Slit lamp base is on
axle and rails, which enables coarse anterior-posterior and lateral movement. It has a locking screw (E) that must be fully unscrewed in the counterclockwise direction before the slit lamp can be moved.
Joystick
The joystick can push the entire slit lamp base to attain approximate focus. The joystick can then be gently tilted for fine movements to bring the image into sharp focus.
Turning the joystick clockwise lifts the entire column up, and a counter-clockwise motion brings it down.
The intensity knob (rheostat) is used to adjust the intensity of the light source. The pictured rheostat is in the off position
Forehead rest and canthus indicator
The patient’s head rests against the support frame: this consists of a forehead rest (H) and a chin rest (I), the height of which may be adjusted using the adjustment knob (J).
The canthus indicator is a black line which should be level with the lateral canthus of the patient’s eye (K).
Light source and beam height
The illumination arm contains the light source (L); this has an adjustable lever with different filter types (M). The lever in the far left position (as pictured) is in the “open” position (i.e. unfiltered light).
The beam height can be adjusted via the centre screw (N). Pictured is a beam height set to 10mm. The cobalt blue light (for fluorescein examination) can be found by rotating the screw counter-clockwise until a click is heard and the dial reads “B”.
Examiner setup
The examiner should adjust the height of the table for comfortable viewing. Ensure the eyepieces are adjusted to allow for a binocular view. This should be tested by closing each eye in turn.
One hand should be placed on the carriage and joystick and the other on the slit-adjustment control. This allows for dynamic adjustment of the angle and intensity of illumination.
Patient positioning
The chair height should be adjusted first. The patient’s chair should be brought forward, and they should rest against the forehead and chin frames, the height of which can be adjusted using the adjustment knob.
The black indicator mark should align with their lateral canthus, and their forehead should be positioned right up against the headrest.
Examination
After switching the slit lamp on, the rheostat should be dialled to 100%, and the filter lever should be set to the far left position to remove any light filters.
The slit beam width should be adjusted to display a beam of light via the controls on the base of the illumination arm.
The microscope should be set to an appropriate magnification (6.3x or 10x), and the carriage moved forward to obtain coarse focusing.
As the image comes into focus, the joystick can be tilted to adjust fine focus. It can also be twisted to move up and down the vertical axis. The height of the beam may be altered using the centre screw on the top of the illumination arm.
Anatomical order of assessment
Lids and lashes
Conjunctive and sclera
Cornea and tear film
Iris and pupil
Lens
Lids and lashes assessment
Guide light to lower and upper lashes, using the joystick. Observe eyelid abnormalities e.g. entropion, ectropion and signs of blepharitis.
Press posteriorly using your fingertip under the patient’s lower eyelid to obtain a better view of the meibomian glands. The meibomian glands of the upper lid can be examined by asking the patient to look down and lifting the lid with your thumb.
Conjunctiva and sclera assessment
Examine all areas by asking the patient to look in all four directions of gaze. Observe for any areas of injection, chemosis or foreign bodies.
The tarsal conjunctiva, found on the posterior surface of the eyelids, can be examined by pressing posteriorly under lower eyelid when the patient is looking up. The upper tarsal conjunctiva can be examined following lid eversion.
Cornea assessment
Begin with a wide beam of light. If abnormalities are identified, make the beam into thin slit and the illumination arm moved to either side so the beam hits the cornea at an oblique angle.
Allows all layers of the cornea to be seen in three dimensions: epithelium (closest to light), stroma, descemet membrane and endothelium (furthest away).
Examples of abnormalities- corneal abrasions and ulcers, foreign bodies and inflammatory cells adherent to the posterior surface of the cornea (keratic precipitates).
