Indications for slit lamp examination of the vitreous include symptoms of floaters and light flashes, to diagnose posterior vitreous detachment with or without retinal complication, and to assess vitreous involvement in intraocular segment inflammation. Several conditions may result in inflammatory cells, red blood cells, or pigment cells moving into the vitreous. These cells will appear as small punctate opacities, suspended or slowly floating within the optically empty spaces between the fibrils and in the retrolental space. Red-brown vitreous cells are very likely to be red blood cells and/or retinal pigment epithelial (RPE) cells. Known as tobacco dusting or Shaffer’s sign, these red-brown cells are usually an indication that a retinal tear or detachment is present so that the RPE cells have become dislodged or associated retinal vessel damage has occurred. Two types of slit lamp illumination can be used to examine the anterior vitreous; parallelepiped and/or optic section. No auxiliary lens is required.

Slit lamp set up for a parallelepiped:
Ø Coupled
Ø 60 degrees beam angle
Ø 1-2 mm beam width
Ø Maximum beam height
Ø No filter
Ø Medium illumination
Ø 10-16X magnification
Ø Use the joystick to sharply focus the microscope and the parallelepiped simultaneously.

Slit lamp set up for an optic section:
Ø Coupled
Ø 60 degrees beam angle
Ø Beam width nearly extinguished
Ø Maximum beam height
Ø No filter
Ø Medium illumination
Ø 10-16X magnification
Ø Use the joystick to sharply focus the microscope and the optic section simultaneously.

Procedure
Starting at the temporal border of the dilated right pupil, move the joystick forward to focus the parallelepiped into the anterior vitreous.
Keep this portion of the vitreous in focus while scanning across the vitreous to the nasal border of the pupil.
Move the joystick further forward so as to focus into the vitreous as far as possible and scan across it to the temporal pupil border.
Repeating this technique with the beam positioned nasally will ensure that the vitreous is thoroughly examined.

Hints and tips
Significant cataract formation can obscure the various vitreous landmarks.
A good deal of observation skill development is needed to accurately assess the presence of vitreous cells.
Also the collapse of the posterior limiting layer of the vitreous in posterior vitreous detachment (PVD) can be easily over looked if the slit lamp is not focussed well into the posterior chamber.
Instruct the patient to move the eye around in order to stir up any vitreal debris.
To distinguish between red blood cells and pigment particles introduce the red free (green) filter.
Red blood cells will appear black and will no longer be visible within the vitreous.
Pigment particles will not absorb the red-free light and will still be visible.

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