Page 142 - The Indian Optician Digital Edition May-June 2023

 Target
1. Distance - fixate at isolated letter, one line
above visual acuity in patient’s poorer eye (with
best correction)
2. Near - accommodative target – reduced
Snellen letters or picture, approximately one line
above visual acuity in the patient’s poorer eye;
patient holds target

 Examiner holds occluder
 Examiner or patient holds prism bar

 Room illumination must be sufficient
to allow examiner to easily observe patient’s
eye movements

 Examiner must be positioned to be able to
see the patient’s eyes but examiner must not
interfere with the patient’s view of the target
STEP-BY-STEP

 Instruct patient to look at the target and to
keep it clear

 Cover-uncover test (to differentiate phorias
from tropias)

 Flip pages at a time and note patient’s test several times to be sure an alternating
response: correct or wrong
tropia or intermittent tropia is not missed.
 cover right eye and observe left eye – ALTERNATE COVER TEST TO DETERMINE
resultant 1: if left eye moves – it is tropia
SIZE AND DIRECTION OF DEVIATION
 now uncover right eye and observe left eye – A. Cover the patient’s right eye, holding the
resultant 2: if both eyes move – it is occluder in front of the eye for approximately
alternating tropia one second, then quickly place it in front of the
 in case left eye does not move – then cover left eye.
left eye and observe right eye – B. Alternate the occluder back and forth
resultant 3: if right eye moves – it is tropia between the two eyes several times, maintaining
resultant 4: if right eye does not move – it is coverage of each eye for one second.
no tropia
C. Observe the movement of the right eye as
DIAGNOSIS OF PHORIAS AND TROPIAS the occluder is moved from the right to the left
BY USING COVER-UNCOVER TEST eye; observe the movement of the left eye as the
occluder is moved from the left to right eye.
The occluder is held in front of the patient’s
eye for one second and eyes are observed as D. Always observe the eye that is being
indicated above. Before the occluder is placed in uncovered for movement.
front of the other eye, a few seconds should be
allowed to elapse so the eyes can return to their E. Responses
normal relationship. Repeat the cover-uncover  No movement - ortho

138 | THE INDIAN OPTICIAN | MAY-JUNE 2023 OPTOMETRY