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Biomicroscopy(Slit Lamp)
PURPOSE To eva luate the health of the anterior segment of the eye．The slit lamp is used in conjunction with auxiliary lenses to view the anterior chamber angle and the retina．The slit lamp is essential in the eva luation of contact lenses on the eye．
EQUIPMENT
·Slit lamp
BASIC COMPONENTS OF A SLIT LAMP
Although slit lamps vary considerably depending on the manufacturer，there are a number of components common to all slit lamps．
Illumination Arm
The illumination arm houses the illumination system．The angle of the arm can be varied from 0°to 90°from the straight ahead position．The following components are located on the illumination arm：
·Slit controls：There are two size controls, one to vary the slit width and another to vary the slit height．There is also a control that varies the orientation of the beam．
·Click stop：The click stop changes the position of the reflecting mirror to alter the angle of the beam with respect to the viewing system．When the mirror is “in click stop．”the focus of the slit beam will be coincident with the focus of the viewing system．
·Filters：The filters are used to vary the appearance of the slit beam．Most slit lamps include a cobalt blue filter, a green or red-free filter, and at least one neutral density filter．
Microscope Arm
The microscope arm houses the viewing system，composed of the objective and ocular lenses．The angle of the microscope arm may be varied，although it is normally kept in the straight ahead position．The following components are located on the microscope arm：
·Oculars：The oculars are adjustable to compensate for the examiner’s refractive error．The distance between the oculars is variable and can be adjusted to match the examiner’s PD．
·Magnification changer：The magnification changer allows magnification to be adjusted either in a stepwise fashion or in a continuous fashion (zoom system)．
Slit lamp Position Controls
·Joystick/elevation knob：These may be two separate controls or a single control. They are found on the instrument base．The joystick controls the forward movement, and therefore the focus, of the slit lamp．It also controls the left to right movement of the slit lamp．The elevation knob controls the height of the microscope．
SET-UP
·The patient is examined without correction．
·The room illumination is dim．
·Disinfect the forehead rest and the chin rest．
·Adjust the height of the instrument table to a comfortable position for both the patient and the examiner．
·Set the reflecting mirror at the click stop position．
·Instruct the patient to place his chin in the chin rest and his forehead against the forehead rest．
·Adjust the chin rest to align the patient’s outer canthus with the demarcation line on the right sport of the head rest．
·Set the magnification on a low setting(6× or 10×)．Remove all filters from the illumination system．
·Instruct the patient to close his eyes．Turn on the instrument．Using the patient’s eyelashes for fixation, focus each ocular by closing one eye at a time and rotating the eyepiece．Always begin with the eyepiece on the highest plus setting(as far counterclockwise as possible)and rotate it clockwise until the image first clears．
·Open both of your eyes and set the slit lamp to your PD(interpillary distance)by adjusting the separation of the oculars．If the PD is set properly，you should obtain a binocular view when looking through the oculars．
·Use one hand to operate both the joystick(to align and focus the microscope)and the elevation knob(to align the microscope)and the other hand to operate the slit controls，to vary the angle between the lamp and the microscope, and to manipulate the patient’s eyelids．
STEP-BY-STEP PROCEDURE
The anterior segment of the eye is usually examined in an anterior to posterior sequence．The structures are generally examined in the following order：lids and lashes, conjunctiva，tear film，cornea，anterior chamber angle，iris，and lens．During a routine slit lamp examination the right eye is usually examined first，followed by the left eye．
LIDS AND LASHES
1．Use diffuse illumination with the illumination arm set approximately 30°from the straight ahead position．
2．Set the magnification on a low setting(6× or 10×)．
3．Instruct the patient to close his eyes．Scan across the per lid and lashes．
4．Instruct the patient to open his eyes．Scan across the lower lid and lashes，observing the tear meniscus，the lid apposition to the globe，and the openings of the Meibomian glands．
CONJUNCTIVA
5．Narrow the beam to wide parallelepiped, with the illumination arm set approximately 30°from the straight ahead position．
6．Keep the magnification on a low setting (6× or 1O×)．
7．Instruct the patient to open his eyes and to look ．
8．Inform the patient that you are going to touch his lower lid．Place your index finger close to the patient’s lower lash margin and evert the lower lid．Scan the inferior palpebral and bulbar conjunctiva looking for elevations，depressions, or discolorations．eva luate the openness of the inferior punctum．
9．Instruct the patient to look down．
10．Inform the patient that you are going to touch his per lid．Place your thumb close to the per lash margin and elevate the lid．Scan across the serior bulbar conjunctiva．
11．Instruct the patient to look first to the left and then to the right．while you scan across the nasal and temporal bulbar conjunctiva．
12．If indicated, evert the per lid at this time (see section on special slit lamp procedures)．
CORNEA AND TEAR FILM
13．Decrease the beam to a narrow parallelepiped，approximately 1 to 3 mm wide．Set the illumination arm approximately 30 to 45°from the straight ahead position(see Figures 5-3 and 5-4)．
14．Set the magnification on a medium setting(16× or 20×)．
15．Instruct the patient to look straight ahead．Scan across the central portion of the cornea looking for any opacities or irregularities．When you reach the apex of the cornea, swing the illumination arm to the other side, set at the proper angle and continue scanning．It may be necessary to back slightly after shifting the illumination arm，so you do not miss scanning part of the cornea．
16．Instruct the patient to look down．Elevate the per lid with your thumb, and scan across the serior one third of the cornea．Remember to shift the illumination arm when you reach the corneal apex．
17．Instruct the patient to look ．Pull down the lower lid with your index finger if necessary, and scan across the inferior one third of the cornea．Remember to shift the illumination arm when you reach the corneal apex．
18．If indicated, specular reflection should be performed at this time(see section on special slit lamp procedures)．
ESTIMATING THE DEPTH OF THE ANTERIOR CHAMBER ANGLE BY THE VAN HERICK TECHNIQUE
19．Set the illumination arm 60°to the temporal side of the patient’s line of fixation．As an alternative, the illumination arm can be set 30°to the temporal side and the microscope 30°to the nasal side, yielding a 60°angle between the lamp and the microscope．
20．The magnification should remain on a medium setting(16× or 20×)．
21．Narrow the beam to an optic section(see Figures 5-5 and 5-6)．
22．Instruct the patient to look straight ahead．
23．Focus the light sharply on the cornea at the very edge of the temporal limbus．
24．Compare the width of the “shadow” formed on the iris(representing the depth of the anterior chamber) to the width of the optic section(representing the thickness of the cornea)(see Figures 5-7 and 5-8)．
Note：The shadow is actually a dark interval between the light on the cornea and the light on the iris, that represents the optically empty aqueous in the anterior chamber．
25．If the angle width is less than or equal to l/4:1，gonioscopy should be performed to eva luate the angle more accurately．
26．If the microscope arm was moved for this procedure (see step 19)，return it to the straight ahead position before proceeding．
IRIS
27．Increase the slit width to a wide parallelepiped, and set the illumination arm 30 to 45°from the straight ahead position．
28．Keep the magnification on a medium setting(16 × or 20×)．
29．Scan across the iris surface，looking for irregularities．Note the pillary light reflex．The pil should constrict when the slit lamp beam reaches the pillary margin．
CRYSTALLINE LENS
30．Narrow the angle of the illumination arm to about 20°from the straight ahead position．
31．Keep the magnification on a medium setting(16 × or 20×)．
32．Reduce the slit beam to a narrow parallelepiped．
33．Slowly move the slit lamp closer to the patient until the light is directed through the pil and becomes sharply focused on the anterior surface of the lens(see Figure 5-9)．Continue to slowly move the biomicroscope closer to the patient to examine the deeper layers of the lens．Focus on the posterior surface of the lens．Look for any opacities，irregularities, or discolorations within the lens．Swing the illumination arm to the opposite side, set at the proper angle, and again examine the lens from the anterior to the posterior surface．
RECORDING
·Record for each eye separately．
·List each structure eva luated and record your observations for each．
·Record any abnormalities or pertinent negatives．
·Drawings and photographs are recommended in cases where they enhance descriptions．
EXAMPLE
0D OS
Clear Lids Clear
Clear Lashes Flaky
Clear Conjunctiva Concretions, inferior palpebral
Small opacity， Cornea Arcus inferiorly
anterior stroma
at limbus 3 o/c
1/2:1 Angle 1/2:1
Flat Iris Flat；nevus at 3:00
Clear Lens Epicapsular stars
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