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PURPOSE To measure a patient’s fine depth perception through his ability to fuse stereoscopic targets．
EQUIPMENT
·Polaroid glasses or red-green glasses depending on the test used．
·Stereo test booklet(eg，Randot，Titmus, Bernell，TNO Test)．
Note：There are stereo tests available that do not need Polaroid or red-green glasses(eg，the Frisby Stereotest, the Lang Stereotest)．These are used chiefly in examining young children who will not tolerate wearing the test glasses．
Stereo may also be tested at distance using the American Optical Vectographic Slide with the patient wearing Polaroid glasses．
SET-UP
·The patient wears Polaroid glasses or red-green glasses over his near correction．
·The patient holds the stereo target at 40 cm(see Figure 2-4).
·The overhead lamp is directed toward the target．
STEP-BY-STEP PROCEDURE
1．Direct the patient’s attention to the smallest set of targets．Frequently this is a set of three or four circles．Ask the patient to tell you what he sees．If the patient is unresponsive, ask him to identify which of the circles in set number one appears closest or seems to be floating above the page．
2. If the patient appreciates stereopsis on the first set of targets, instruct him to go on to the next set．If the patient does not appreciate stereopsis，go to step 4 below．
3．Continue testing until the patient gives two consecutive incorrect answers．
4．If the patient is unable to correctly identify the floating object in the smallest set of targets，repeat steps 1 and 2 using the medium sized targets．Ask the patient again to identify the object that is floating above the page．If the patient identifies all of these correctly，go back and try the smallest set of targets again．
5．If the patient is unable to correctly identify any of the medium sized targets，show the patient the large targets and ask him to identify what he sees．To verify a correct response, ask the patient to show you in space where he sees the target．If the patient identifies all of the large targets correctly go back and try the medium and small sets of targets again．
RECORDING
·Write “Stereo at N”(near)．
·If done without correction，record “sc”; if done with correction，record “cc．”
·Record the amount of stereopsis in seconds of arc (taken from the instructions that come with the stereo test) for the last correct response the patient gave before two consecutive incorrect responses．
·If the patient is not able to correctly identify any of the small targets on the test, record the amount of stereopsis in seconds of arc for the smallest target the patient was able to correctly perceive．
·If the patient does not perceive any of the stereo targets，record “No stereo．”
·Record the name of the test used．
EXAMPLES
Stereo at N sc 40 sec，Titmus
Stereo at N sc 20 sec, Randot
Stereo at N sc 3000 sec，Stereo Fly
Stereo at N cc none，Randot
EXPECTED FINDINGS
Stereo at near：40 seconds of arc or better． |
