SLIT LAMP(METHODS OF ILLUMINATION)

By: Maclester

DIFFUSE ILLUMINATION

• Gives a good overall picture of the eye, but no fine details. It is used primarily for a general survey of the eye.

• Can observe the entire extent of a corneal scar or infiltration.

• The presence of folds in Descemet's membrane become visible.

• The presence of any invading blood vessels in the cornea is disclosed.

• Edema of the epithelium may be indicated by a hazy, gray, and somewhat granular appearance.

• Observe: eyelids, lashes, conjunctiva, sclera, pattern of redness, iris, pupil, gross pathology, and media opacities

Lids

Conjunctiva

Cornea

OPTIC SECTION

• To discover thickening, thinning, and distortions in the corneal contour.

• To determine the depth of foreign bodies or opacities in the corneal substance. One way of describing depth is as a percentage of the total corneal thickness.

• To see a wide slice of stroma. (The angle between the microscope and illuminating arm can be increased.)

• To perceive the flare or relucency in normal aqueous. The luminous beam is directed so that the upper portion of the beam enters the lower part of the pupil. This permits dark areas immediately above to serve as a dark contrasting background. The presence of appreciable flare is indicative of a pathological state.

Conjunctiva

Cornea

Lens

Vitreous

PARALLELEPIPED

• Gives a broad view of the anterior and posterior corneal surfaces.

• Gives a view of a wide block of substantia propria.

• To determine anterior surface irregularities.

• Used to examine the endothelium.

• To make a general survey of the cornea: • Opaque features in the cornea such as scars, abrasions, nebulae, blood

vessels, and folds in Descemet's membrane reflect the light and thus appear whiter than the surround. These should also be examined under retro-illumination.

• Corneal nerves appear under higher magnification as fine white silk threads usually branching into a Y (seen mostly in middle third of stroma).

• Corneal epithelial edema is only seen poorly with a parallelepiped but gives an increased gray whitish appearance in the affected area. The best method for seeing edema is by retro-illumination.

• Used to determine the fit of a contact lens after fluorescein has been instilled in the eye.

• With the aid of fluorescein areas of epithelial embarrassment or erosion will stain and therefore appear much greener than the surround.

Cornea

RETRO-ILLUMINATION

• Retroillumination is used to evaluate the optical qualities of a structure.

• The light strikes the object of interest from a point behind the object and is then reflected back to the observer

DIRECT RETROILLUMINATION FROM THE IRIS

INDIRECT RETROILLUMINATION FROM THE IRIS

• The beam is directed to an area of the iris bordering the portion of the iris behind the pathology

• This provides a dark background, allowing corneal opacities to be viewed with more contrast

RETROILLUMINATION FROM THE FUNDUS (RED REFLEX)

• The slit beam at 2 to 4 degrees

• Shorten the beam to the height of the pupil to avoid reflecting the bright light off of the iris.

• Focus the microscope directly on the pathology using 10X to 16X magnification. Opacities will appear in silhouette.

• This view is best accomplished if the pupil is dilated.

SPECULAR REFLECTION

• Specular reflection is used to visualize the integrity of the corneal and lens surfaces. If the surface is smooth, the reflection will be smooth and regular; if the surface is broken or rough

• Position the illuminator about 30 degrees to one side and the microscope 30 degrees to the other side

• To visualize the endothelium, start with lower magnification (10X to 16X). Direct a relatively narrow beam onto the cornea

• Switch to the highest magnification available.

• Endothelium is best viewed using only one ocular.

SCLEROTIC SCATTER

• A tall, wide beam is directed onto the limbal area.

• When the light is properly aligned with regard to the eye, a ring of light will appear around the cornea.

• The light is absorbed and scattered through the cornea

highlighting pathology.

• Use 10X magnification, with the microscope directed straight ahead

• Observe: general pattern of corneal opacities

TANGENTIAL ILLUMINATION

• This technique is used to observe surface texture.

• Medium-wide beam of moderate height

• Swing the slit lamp arm to the side at an oblique angle

• Magnifications of 10X, 16X, or 25X are used

• Observe: anterior and posterior cornea, iris, anterior lens (specially useful for viewing pseudoexfoliation)

Cornea

• Wide slit beam

Iris

Lens

• Moderate slit beam

CONICAL BEAM

• Cells, pigment or proteins in the aqueous humour reflect the light like a faint fog. To visualise this the slit illuminator is adjusted to the smallest circular beam and is projected through the anterior chamber from a 42° to 90° angle. The strongest reflection is possible at 90°

Aqueous flare-

Tyndall’s

phenomenon

OSCILLATORY ILLUMINATION

• A beam of light is rocked back and forth by moving the illuminating arm or rotating the prism or mirror. Occasional aqueous floaters are easier to observe. Can also be used to determine the extent of opacities in the crystalline lens.

VAN HERRICK TECHNIQUE

• Use to evaluate anterior chamber angle without gonioscopy• Medium magnification

• Angle 60 degrees• Narrow beam close to limbus

• Depth of anterior chamber is evaluated it to the thickness of cornea:

4. grade – open anterior chamber angle 1:1 ratio

3. grade – open anterior chamber angle 1:2 ratio2. grade – narrow anterior chamber angle1:4 ratio1. grade – risky narrow anterior chamber angle less than 1:4 ratio

0. grade – closed anterior chamber , cornea “sits” on iris

Reference

• Haag-streit slit lamp imaging guide

• http://en.wikipedia.org/wiki/Slit_lamp

• http://optometry.berkeley.edu/class/opt260a/labs_pp/labslitlamp.htm

• http://cal.vet.upenn.edu/projects/ophthalmology/ophthalmo_files/Tools/BIOMICROSCOPY.pdf

•Thank you