Slit Lamp Biomicroscopy Part One

Slit Lamp Illumination Types
Associated Ocular Conditions And
Slit Lamp Examination Procedures
Direct Illuminations:
1.) Diffuse:
Diffuse illumination or "wide beam" illumination deserves a short separate discussion from the other types of illuminations. The term diffuse has been carried over from earlier writings when slit lamps had either diffusing filters or independent racking microscopes. This allowed each to be independently focus on different structures. Most of today's slit lamp biomicroscopes have their light sources and microscope coincident to one another and are focused on the same structure at the same time. Diffusing filters are still found in some slit lamps and are used in photographing the anterior segment of the eye. "Wide beam" illumination is the only type that has the light source set wide open. Its main purpose is to illuminate as much of the eye and its adnexa at once for general observation.

A wide, un-narrowed, beam of light is directed at the cornea from an angle of approximately 45 degrees. Position the microscope directly in front of the patient's eye and focus on the anterior of the cornea. Low to medium magnification
(7 - 16x) should be used which allows the observer to view as many of the structures as possible. When viewing the eye with achromatic light one should note, on gross inspection, any corneal scars, irregularities of the lids, tear debris, irregularities of Descemet's membrane or pigmentary changes found in the epithelial layer, etc. These findings are investigated more thoroughly with other types of illumination.

With the aid of the cobalt blue filter and either fluorescein sodium or Fluoresoft® permit the evaluation of bearing, movement, positioning of contact lenses. Using the cobalt blue filter and fluorescein sodium this is a reasonable illumination for assessing a patient's tear break up time (TBUT), dark drying areas of the epithelium. Staining of the cornea and conjunctiva can also be assessed. Fluorescein sodium dye will stain the cornea and conjunctiva any time the epithelium is compromised. Fluorescein dye does not stain epithelial cells themselves, but pools within the intercellular defects thus highlighting the damaged area. Fluorescein staining is relatively nonspecific, occurring with any condition affecting epithelial integrity. Do not confuse "negative staining" for true TBUT. Negative staining is often seen when checking TBUT or evaluating an area that has stained in the past. "Negative staining" results because of irregularities in the corneal epithelium. These dark areas are where the tears separate quickly rather than stain tissue. Examples: Map and dot dystrophies, micro-cystic edema, healing but still rough and not smoothly healed abrasions, etc. The cobalt blue filter is also helpful in detecting Fleischer's Ring or Line in keratoconus and Hudson Stahli's Line in older patients.

Using Rose Bengal and no filters will show a pink staining of epithelial cell damaged tissue as in cases of keratoconjunctivitis Sicca, herpatic lesions of the lids and cornea and other ulcer margins. Other types of illumination are better for evaluating the degree and depth of any staining. See color plates in Dr. Casser's book.

Diffuse, wide-beam, illumination together with the red free (green) filter is helpful when viewing the bulbar conjunctiva, and episcleral blood vessels. With the aid of the red free filter small hemorrhages, aneurysms and engorged vessels stand out. It is not difficult to differentiate between conjunctival, episcleral, and scleral injection. Conjunctival vessels are obviously fairly superficial and are movable upon friction from the eyelid, whereas less superficial and deep vessels show minimal to no movement with the overlying conjunctiva. Deeper episcleral injection may also appear somewhat darker and give an overall purplish hue. (Abelson et al) proposed a standardized grading system for judging the different types of injection.

A) Ciliary Injection B) Episcleral Injection C) Conjunctival Injection

Grade Severity

0 White and Quiet

1/2 Slight, Usually Normal

1 to 1+ Mild

2 to 2+ Moderate

3 to 3+ Severe

Adapted and modified from Abelson, M. et al.

2.)Direct Focal
a.) Optic Section: Optic section is used primarily to determining the depth or elevation of a defect of the cornea, conjunctiva or locating the depth of an opacity within the lens of the eye.

With the optic section as mentioned above, it is possible to detect changes in corneal and conjunctival thicknesses, to assess depths of foreign bodies, scars and opacities, to estimate the anterior chamber depth and to identify the anatomical location of cataracts within the crystalline lens. The biomicroscope should be directly in front of the patient's eye, the illumination source at about 45 degrees and the illumination mirror in "click" position. The slit width is almost closed, about 0.25 mm wide and 7 to 9 mm high. First place the magnification on low to medium (7 - 10 X) and focused on the patient's closed lid. The thickness of the eyelid is about 1 mm thick, which means focusing on the cornea is accomplished by only slightly moving the joystick forward. Have the patient open their eyes, give the patient a point of fixation such as the fixation light, part of the biomicroscope, or the top of the your opposite ear. Once the cornea is in sharp focus, try scanning the cornea from temporal limbus to nasal limbus. To maintain a clear, distortion-free view, the illumination source is always moved to the opposite side when crossing the mid-line of the cornea about at the center of the pupil.

With a clearly focused optic section slightly temporal to the center of the cornea, increase the magnification to 16x then to 20x and illumination brightness and note the following:

1) The Front Surface Bright Zone Is The Surface Of The Tears
2) The Next Darker Gray Line Is The Epithelium Layer
3) The Next Brighter Thin Line Is Bowman's Membrane
4) The Gray Wider Granular Area Is The Stroma Zone
5) The Last Bright Inner Zone Is The Endothelium

To attain an optic section of the crystalline lens, the angular separation of the illumination source is reduced until the light beam just grazes the edge of the pupil and the vertical height can be reduced to approximate the pupil size. This alignment can easily be accomplished from outside the biomicroscope. When the beam cuts just across the edge of the pupil, the crystalline lens will appear sectioned. By focusing the biomicroscopes with one hand and controlling the direction or angle of the light source with the other hand, the different layers of the lens can be brought into focus; hence, the anatomical location of any opacity can be determined. Furthermore, the degree of nuclear opalescence and color can be evaluated and graded via the, lens opacities classification system II (LOCS II)[Chylack, 1989]. Different magnifications may be used, but medium and high give the best detail.

Van Herick's technique for grading the anterior chamber angles uses an optic section placed near the limbus with the light source always at 60 degrees. The biomicroscope is placed directly before the patient's eye. This technique only allows you to judge the temporal and nasal angles.

Van Herick Angle Estimation Method

Angle Grades Risk of Angle Closure Cornea to Angle Ratio

4
Wide Open Angle; Incapable of Closure. Iris to Cornea Angular Separation Equals 35-45⁰.

Anterior Chamber Depth (Shadow) is Equal to or Greater Than Corneal Thickness

3
Moderately Open Angle; Incapable of Closure. Iris to Corneal Angular Separation Equals 20-35⁰

Anterior Chamber Depth (Shadow) is Between 1/4 and 1/2 the Corneal Thickness

2
Moderately Narrow Angle; Closure Possible. Iris to Corneal Angular Separation Equals 20⁰

Anterior Chamber Depth (Shadow) is Equal to 1/4 the Corneal Thickness

1
Extremely Narrow Angle; Closure Probable. Iris to Corneal Angular Separation Equals 10⁰

Anterior Chamber Depth (Shadow) is Equal to Less Than 1/4 the Corneal Thickness

0
Basically Closed Angle; Closure is Most Emanate. Iris to Corneal Angular Separation Equals 0⁰

Anterior Chamber Depth (Shadow) is Only a Very Narrow Slit or no Anterior Chamber Angle

Adapted from: Van Herick W, Shaffer RN, Schwartz A. Estimation of width of angle of anterior chamber. Am J Ophthalmol 1969;68:626-9.

Optic section using the Van Herick Technique to grade the anterior chamber depth. This is a grade 1 or narrow angle.

The "Split Limbal Technique" allows you to make an estimation of the superior and inferior angles. The slit lamp and illumination system are in click position aligned directly in front of the patient. The beam width is that of an optic section, which is focused on the limbal cornea junction thus, splitting the cornea and limbus. The doctor then views the arc of light through the cornea and that falling on the iris without the aid of the slit lamp. The angular separation seen at the limbus corneal junction is an estimation of the anterior chamber angle depth in degrees.

"Split Limbal Technique"
Which Is Observed With The Naked Eye

Grade Angle

+ 4 TO 4 - ( 45 - 35⁰ )

+ 3 TO 3 - ( 35 - 20⁰ )

+ 2 TO 2 - < 20 BUT > 10⁰)

1 - 0 ( 10⁰ OR LESS )

b.) Conical Beam: Examination of the anterior chamber for cells or flare must be performed before either dilation or applanation tonometry. Magnification
16 - 20x and illumination (high) or what the patient will tolerate. Dilation often results in an increase in the number of cells and fluorescein used in applanation tonometry causes an increase in flare [Schlaegel, 1982]. This type of illumination is used to detect floating aqueous cells and flare by the, Tyndall effect, much like seeing dust floating in the air of a sun filled window.

The traditional method of locating and grading cells and flare is to reduce the beam to a small circular pattern with the light source 45 to 60 degrees temporally and directed into the pupil. Position the biomicroscope directly in front of the patient's eye with as bright illumination as the patient will permit and high magnification. The examiner always allows themselves a period of time to dark adapt. The conical beam is focused between the cornea and the anterior lens surface and observation is concentrated on the dark zone between the out of focus cornea and lens. This zone is normally optically empty and appears totally black. Flare (protein escaping from dilated vessels) makes the normally optic empty zone appear gray or milky when compared to the uninvolved eye. Cells (white blood cells escaping from dilated vessels) will reflect the light and be seen as white dots. The following techniques have been suggested: either to oscillate the light source with the joy stick from left to right while focused in the anterior chamber or to focus from the posterior cornea to the anterior lens while oscillating the light source. These techniques are not typically used clinically

The following is a more traditional technique and one that works well clinically and is superior when grading the severity of inflammation. Use a parallelepiped approximately 2 mm wide and 4 mm high. Focus on the iris near he pupil then pulled back the focus into the anterior chamber so light is seen passing through the out-of-focus cornea and lens. The examiner waits and watches the dark zone between the out-of-focus cornea and the light passing through the pupil and lens. The convection currents of the aqueous will move any protein or cells up and through this zone. You watch and count the number of cells seen during a minute period.

Grading Cells and Flare
Grade Aqueous Cells Grade Flare

0
None
0
Optically Empty Compared Bilaterally

1
2-5 Cells Seen in 45 Seconds or One Minute
1
Faint: Haze or Not Equal Bilaterally

2
5-10 Cell Seen at Once
2
Moderate: But Iris Detail Still Clear

3
Cells Scattered Through Out Beam 20 or More
3
Marked: Iris Details Becoming Hazy

4
Dense Cells in Beam, More Than You Can Count
4
Dense Haze: With Obvious Fibrin Collecting on Iris

READ VOL. 4 - CHAPTER 32 IN "DUANES' CLINICAL OPHTHALMOLOGY"

Cells and flare in the anterior chamber represent a condition of great concern and are usually diagnostic of an inflammation. However, if cells or flare are not seen, but an inflammation is suspected, use the "Consensual Pupillary Reflex" test "Henkind" test or "Consensual Pain Reflex" test, all one and the same, to help confirming an inflammatory diagnosis. The patient completely covers the eye in question so no light can enter. They are to report any discomfort when the slit lamp is turned on in front of the "good eye" and the brightness is turned up. If he/she reports discomfort, cells and flare may not be present, but there most likely is a smoldering inflammation that has not resolved or is about to develop [Au, 1981].

Grading the Consensual Pain Reflex
Grade Patient Response

1 To 1+
Definite Pain Without Acute Distress

2 To 2+
Causes Wincing or Complaint of Pain

3 To 3+
Causes Withdrawal From the Light

4 To 4+
Severe Allows No Light in the Eye

C.) Parallelepiped: A parallelepiped is one of most common types of illumination used. It is used in combination with a number of different types of illuminations. The biomicroscope should be directly in front of the patient's eye, the illumination source at about 45 degrees and the illumination mirror in "click," position. A parallelepiped is essentially an optic section, except the slit width is greater (2.0 - 4.0 mm) and the height may vary, providing a more three dimensional view of the cornea or crystalline lens. The three-dimensional view permits observation of distinguishable details within the crystalline lenses "zones of discontinuity". As with the optic section, the angle between the illumination source and biomicroscope may be varied to expose more corneal epithelium, stroma and endothelium. The whole cornea should be scanned using a parallelepiped. When scanning the cornea, a clear undistorted view must be maintained by positioning the light source to the opposite side when crossing the mid-line of the cornea. Both normal and abnormal findings can be seen when scanning the cornea with varied levels of magnifications and brightness. Look for any of the following:

Tear debris is usually benign and related to allergies or sinus conditions, but may correlate with bacterial infections.
Corneal nerves are white thread-like structures that bifurcate and trifurcate and are located anywhere within the cornea.
Blood filled vessels extend from the limbus onto or into the cornea, and are diagnostic of chronic or acute insult or inflammation.
Ghost vessels extend from the limbus onto or into the cornea. They are empty of blood and diagnostic of some type of past corneal insult or inflammation.
Corneal scars are white in color and diagnostic of some past corneal damage, ulcer, abrasion or foreign body.
Corneal striae are white usually vertical thread-like twisting lines found in Descemet's membrane and posterior stroma. They are diagnostic of poor soft contact lens fitting, diabetes or metabolic changes as with the reduced number of endothelial cells of the elderly. They are the result of overall thickening of the entire cornea and buckling of the back surface.

Grades of Cornea Striae
Grade Observed Number

0 None

1 Less Than Five

2 Five To Ten

3 Ten To Twenty

4 More Than Twenty

Endothelial pigmentation when heavy and located vertically on the endothelium is known as "Krukenberg's Spindle", it may be diagnostic of iris atrophy and pigmentary glaucoma. Transillumination of the iris should be performed and any transillumination iris defects (TID's), holes in the iris, noted. Scant, very fine deposits are commonly seen and not pathological.

3.) Retro-Illumination: Usually uses a parallelepiped that bounces unfocused light off one structure while observing the back lighting of another. The alignment and angular separation of the biomicroscope to the illumination source will vary. The light source beam is reflected off another structure like the iris, crystalline lens or retina while the biomicroscope is focused on a more anterior structure. Retroillumination or transillumination the iris or crystalline lens uses low to medium magnification
(7 - 10x). The slit width 1 - 2 mm wide and 4 - 5 mm high with the biomicroscope and light source placed in direct alignment with each other. They are both positioned directly in front of the eye to be examined. Focus the slit just off the edge of the iris and on the front of the lens. If there are defects or atrophy of the iris they will be seen as a retinal "orange" glow coming back through each defect or hole. Patients who have numerous endothelial pigment deposits you must transilluminate their iris. Remember the term transillumination iris defects or (TID's). See color plates in Dr. Casser's book. Furthermore, retroillumination of the crystalline lens is required to classify and grade both cortical and posterior subcapsular cataracts using LOCS II.

The cornea is probably the most common structure viewed in retro-illumination. Keratic precipitates (accumulation of white blood cells and fibrin) will appear white in direct illumination but dark by retro-illumination. This technique is valuable for observation of deposits on the corneal endothelium and invading blood vessels. According to some authors this is the only way by which tiny rod-like fibrin flecks may be seen on the back of the cornea, warning the so-called "quiet iritis" is still active. Retro-illumination is regarded by most optometrist to be second in importance only to direct illumination.

4.) Sclerotic Scatter: This illumination uses a parallelepiped at the limbus to scatter light internally throughout the cornea. Use low 6 - 10x magnification. In the case of central corneal clouding (CCC) the biomicroscope is not used. The pupil is observed with the naked eye from an angle directly opposite from the light source.

5.) Indirect-Lateral-Proximal: Place the biomicroscope directly in front of the patient's eye and the illumination light source at about 45 degrees. Make sure the illumination mirror is in "click" position. Use a parallelepiped beam sharply focused on a given structure like the cornea. The light passes through the cornea and falls out of focus on the iris. The dark area just lateral or proximal to the parallelepiped is the indirect or proximal zone of illumination. This is the area of the cornea which one surveys through the biomicroscope. This type of illumination is widely used for observation of the corneal epithelium and tears. Most helpful in detection of mycrocystic edema, faint corneal infiltrates and other types of irregularities of the epithelium and tears. Because it utilizes direct, indirect and retroillumination simultaneously, one should consider it to be as important as any other type of illumination.

Keratic precipitates on the endothelium of the cornea as seen in direct, indirect, and retroillumination using a parallelepiped.

6.) Specular Refection: Again a parallelepiped is used. This is the only means by which one is able to view the endothelial cells of the cornea or the epithelial cells on the back of lens. The cells are seen only by one eye and they appear in the ocular opposite from the direction of the illumination light source.
The basic requirements for specular reflection are as follows:

1) The angle between the illumination source and biomicroscope is approximately 60 degrees.
2) High magnification must be used.
3) High illumination is needed.
4) A parallelepiped beam of light is used.

Place he biomicroscope directly in front of the patient's eye and the illumination light source at 45 - 60 degrees. Just off the limbus, obtain a sharply focused parallelepiped of the cornea. Slowly advanced it across the cornea until a dazzling reflection of the filament is seen within the biomicroscope. This reflection is only seen by one eye the other eye is not bothered. Keeping the reflected light within the biomicroscopes field of view, the focus is moved back toward the endothelial cells. There will be a point where two images of the filament are seen, one bright, and the other ghostlike or copper-yellow in color. Critically focus the biomicroscope on the latter until a mosaic of hexagonal cells are seen. It should be noted that even with 40x magnification the endothelial cells do not look as large as most texts show. They resemble the appearance of the dimpled surface of an orange peel or basketball. When the slit lamp's illumination system and the biomicroscope are at equal angles of incidence and reflection the cornea's endothelium is viewable. Both front and back surfaces of the crystalline lens can also be viewed using specular refection.

Positioning The Patient In The Slit Lamp

1.) Procedure:
Inform the patient what you are going to do and why. For Example: This is a slit lamp biomicroscope and I'll be examining the general health of your eye.
2.) Head Position:
A.) Tell the patient what you want them to do: chin in the chin rest and forehead up against the headrest. For professional and hygienic reasons always place a facial tissue on the slit lamp's chin rest. You should have already cleaned the head and chin rest with an alcohol swab. This is always done between every patient. This not only helps keep things more antiseptic, but also makes the slit lamp smell clean and more professional.
B.) Make sure the patient not only looks comfortable but is comfortable. Their forehead tight against the headrest, chin firmly down on the chin rest and their outer canthus aligned with the black marker on the slit lamp post. At this point it is a good idea to reach around and gently pull their head slightly forward against the headrest.
3.) Fixation Instructions:
The patient must be given fixation instructions, where you want them to look. This might be the fixation light, part of the slit lamp or just past your ear.
4.) Pre-Alignment And Focusing:
Tell your patient to close their eyes and relax while you get things aligned. Turn the biomicroscope on and focus the light source on the patient's lid. The eyelid is only about 1 mm thick, therefore, when you instructed the patient to open their eyes you should almost be in focus on the tear film of the cornea.

Suggested Slit Lamp Examination Procedure
(1) (2)

Using a broad beam or better a 2 to 4 mm wide Parallelepiped Type Illumination, Magnification 10-16x, Illumination on low at 45 Degrees, Examine both the upper and lower lids and lashes. The patient's eyes are open and the illumination source is moved at the midline of the lid.

Have the patient look to their left, light source to your left at approximately 45 degrees. The microscope is set straight ahead. Scan and examine the temporal bulbar conjunctiva

(3) (4)

Have the patient look to their right, light source to your right at approximately 45 degrees. The microscope is set straight ahead. Scan and examine the nasal bulbar conjunctiva.

Have the patient look up, retract the lower lid, examine the lower bulbar, lower Palpebral conjunctiva and inferior cornea. The light source should be moved across to the opposite side at the midline of the eye. The microscope is set straight ahead.

(5) (6)

Have the patient look down, retract the upper lid, examine the upper bulbar conjunctiva and superior cornea. The light source should be moved across to the opposite side at the midline of the eye. The microscope is set straight ahead.

Use a Parallelepiped, 16X magnification, light source at 45 degrees and the microscope set straight ahead. Scan and examine the cornea. The light source should be moved across at the midline of the cornea.

(7) (8)

Use a full length Optic Section, magnification 16X, light source at 60 degrees and the microscope set straight ahead. Evaluate and grade the temporal and nasal angles using the Van Herick Technique.

Use a narrow Parallelepiped, 16X Magnification, light source at 45 degrees and the microscope set straight ahead. Examine the iris, crystalline lens and the anterior vitreous body.

Important: Always, pull the slit lamp back, shut off the instrument, and lock it down at the end of any procedure.
The above is only intended as a schematic and students are encouraged to develop any order with which they feel comfortable. It should be pointed out that all steps in the schematic are relevant and should be part of the procedure.

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