October 4, 2013 | POSTED BY | Articles, Clinical Optometry, Optometry School
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When learning how to use the slit lamp one of the hardest parts is keeping the illumination techniques straight. In the beginning it may seem difficult to remember what each lighting is used for, or how to achieve each type of illumination, but given practice and hard work it will come.

Diffuse

direct ottawa

Image courtesy of University of Ottawa

Use: A broad beam diffuse lighting is used for scanning lids, lashes, conjunctiva and the iris. It is good for seeing a large area of tissue without needing to section it into various depths.

Size: Beam is full height, (12mm) and 3-8mm wide.

How: Broaden the beam width so that way it is 3-8 mm wide, and move the lighthouse towards a 30 degree angle.

Parallelpipped

parallel pipped uottawa

Image courtesy of University of Ottawa

Use: Parallelpipped is primarily used for scanning tissues when you want to see specific layers of tissue. The beam width of a parallel pipette is less than diffuse but larger than an optic section. Using a parallel pipette allows for finer focus than using diffuse illumination while allowing you to view more tissue than you would with an optic section.

Size: Beam is at full height, width is around 5-7 mm.

How: Beam size is full height and width is smaller than diffuse but larger than an optic section. The lighthouse should be at a 45-50 degree angle and moving in the same direction as you are scanning. The larger the angle that the lighthouse is extended the more tissue that you will see. When the parallelpipped is in focus on the cornea you will see 3 sections, with the middle line in focus.

Optic section

optic section pacific u

Image courtesy of Pacific University

Use: Optic section is a thin beam that is used for identifying structures, noticing thinning in the cornea as well as measuring van Herrick angles.

Size: Beam height full, beam width as narrow as possible without turning off the light.

How: Narrow the beam width as much as possible. Lighthouse should be at a 45-50 degree angle.

Retroillumiation

Posterior_capsular_opacification_on_retroillumination

Use: Retroillumination utilizes the reflection of light off of the back of the eye to back lighting structures. It is useful when seeing if peripheral iridotamies are still patent (if  they are still open one should see a red reflex shining through the hole) as well as visualizing cataract spoking in cataracts.

Size: Broaden the beam so that it is slightly larger than a parallelpipped.

How: Start in focus at the level of tissue that you are scanning. Swing the lighthouse towards the opposite side until you see a red glow.

Image courtesy of Wikipedia

Specular reflection

specular reflection columbia

Image courtesy of Edward S. Harkness Eye Institute

Use:  Specular reflection is used to analyze the corneal endothelial cells primarily to look for Fuch’s dystrophy, as well as looking at the structures of the anterior and posterior lens capsule.

Size: Full beam height, same width as a parallelpipped, lighthouse 30 degrees away from click position.

How: Begin with a parallelpipped focused on the structure you are trying to examine. Move the lighthouse towards the white box reflecting off of the cornea until your light beam and the box almost touch. The structure you are trying to examine should have an orange peel like appearance. Once this orange peel like appearance begins to appear slightly refocus to obtain a sharper focus on the corneal endothelial cells. To examine more of the corneal endothelium it helps to have the angle of the light beam wider.

Indirect Illumination

indirect illumination

Image courtesy of Root Atlas 

Use: With indirect illumination the light is focused on an area of the eye that you are not looking at. This is used primarily for checking the anterior chamber, where if you used direct illumination you would not be able to see any cells and flare.

Size:  Small beam the same height of the pupil, or a conical beam, width 3-4 mm, lighthouse 30-40 degrees from click position.

How: Focus on the cornea, then focus on the anterior lens capsule, trying not to hit the iris in the process as this would ruin the dark adaptation necessary to visualize the cell and flare. After focusing on the anterior lens capsule move halfway in between the two structures so that you are focused on the dark anterior chamber. You want to have your beam be at enough of an angle that you have a wide area that is darkened, as this is the area that you are searching in for the cells or flare. Use a small parallelpipped to search the anterior chamber for the presence of cells and flare and use a small conical beam to grade the amount of cells and flare present.

Feel free to add any of your own tips or suggestions below!