this ppt is based on eye related medical education.

1. ASSESSMENT FOR
EXTRAOCULAR
MUSCLE PARESIS
By :
A .Dharanikumar

2. ASSESSMENT FOR EXTRAOCULAR MUSCLE
PARESIS
When paresis of one or more EOMis suspected as cause of
squint, in addition to the duction test and version test,
following tests should also be performed:
• Abnormal head posture
examination
• Diplopia charting

4. DIPLOPIA CHARTING
1. Thi test is indicated in patients complaining of confusion or double Vn
2. The test is easy to perform when the pt is co-operative.
3. To perform the diplopia charting, pt is asked to wear red-green goggles; red
glass
being in front of the RE and green in front of the LE.
4. The pt is made to sit with his/ her head straight in a semidark room and
is shown a fine linear light from a distance of 4 ft.
5. The light is moved from primary position into all of the other eight
directions of gaze. For each direction, pt asked to comment on the
position, brightness and separation between the red and green images.

5. From the patient’s comments ,examiner notes following points:
● Whether horizontal diplopia is homonymous or heteronymous.
● Whether the image seen by right eye (red image) is higher or lower than the
image seen by the left eye (green image) or vice versa.
● In which direction of gaze, separation between red and green images is
greatest.
● Whether there are any directions in which fusion is present
In a modified test of Franchchetti, instead of red green goggles, a red
Maddox rod is placed in front of RE and white Maddox rod in front of the LE
and the pt fixates on a spotlight which is seen as vertical red line with RE and
vertical white line with LE.

6. Disadvantages of diplopia plotting test
• This test is only qualitative.
• Test requires intelligent patient - to comment where the separation
is max.
• It is not possible to perform the test in colour blind patients.
• This test is not of use in congenital palsies and those of long-
standing onset,
because due to deep suppression diplopia cannot be elicited.

7. QUANTITATIVE MEASUREMENT OF ACTIONS
OF
EXTRAOCULAR MUSCLES
•This measurement is essential to comment about the paretic muscles
and the pathological sequelae of the paralysis
- overaction, contracture ,secondary inhibitional palsy.
• It is based on haploscopy
- PRINCIPLE : It is described by Burian
- I n the presence of normal retinal correspondence, the two test objects
presented to the two eyes will be superimposed, if they stimulate the foveae
of the two eyes, irrespective of the position of the two eyes.

8. Commonly used haploscopic
tests
have a graphic record of the relative power of
extraocular muscles in all directions of gaze
include:
● • Lancaster red-green test,
● • Hess screen test, and
● • Lees screen test.

9. Lancaster red-green test
● It is a haploscopic test.
● It utilizes a Lancaster red-green screen which is
window- shade type of screen that can be rolled up
when not in use.
The screen contains horizontal and vertical
lines forming squares of 7 cm
● All the squares are of the same size and the tangential
error is not taken into account.

11. ● While performing the test, the patient’s eyes should be in level with the
centre
zero mark, and he/she can be seated at either 1 or 2 metres.
● At 2 metres, each square subtends an angle of 2° = 3.54;
at 1 metre it subtends an angle of 4° = 74.
● Pt is given a R-G reversible goggles green flashlight that project linear
image
● The examiner has a similar red flash light and projects the red streak of
light on
the zero mark on the screen.
● The pt is asked to super impose his/her green light on the examiner’s red
light.

12. •The distance b/w the streaks of light represents the measurement
of the objective deviation provided retinal correspondence is
normal.
• The results are plotted on a chart that is an exact replica of the
screen.
• Since the projected image is a line, the patient's response may
indicate the
presence of cyclotropia, when his/her streak is tilted.
• This test is most useful in patients with ocular paralysis and least
useful in
patients with heterophoria or intermittent heterotropias.

13. Hess screen
test
Principle:
The Hess screen test is based on the haploscopic principle.
-- It utilizes the Hering's law of equal innervation :
In all voluntary movements of the eye, equal and
simultaneous innervation flows from the brain to the
muscles of both eyes
concerned in the respective direction of gaze.

14. Hess screen
test
Prerequisites
1. Full understanding about what he/she is supposed
to do, since the test is purely
2. 2. Good vision in both eyes.
3. 3. Central fixation.
4. 4. Normal retinal correspondence.

16. Discription of conventional Hess
screen
● Original Hess screen consisted of a single tangent screen made up of a
black
cloth 3 ft wide × 3½ ft long, marked by a series of horizontal and vertical
red lines
● The distance between each line subtends a visual angle of 5°.
● Fixation points are indicated at the centre of the screen and at the
intersections
of the 15° and 30° lines by red dots.
● Thus, the red dots form an inner square of 8 dots along the 15° lines and
an outer
square of 16 dots along the 30° lines.
● The inner square represents the 8 cardinal directions of gaze and the
outer square the extreme directions of gaze. In the original Hess

17. ● The end of central vertical green cord is fastened to a movable black
rod 50
cm long
● The ends of the other two green cords, forming upper two limbs of the
letter Y, are kept taut by black threads that pass through loops to small
weights at corresponding upper corners of the screen.
● This arrangement enables the patient to move the indicator freely and
smoothly over the whole surface of the screen in all directions.

18. Modified wooden Hess screen. One of the modifications of the original Hess
screen is a wooden screen with small red lights forming the fixation points and a
green dot light projecter as the indicator. Presently, it is more commonly in use.

20. Procedure Hess screen
test
● The pt wears red-green goggles
● Testing distance = 50 cm
● The pt now sees the fixation points (red light) with one eye and the
indicator
(green light of projector) with the other eye.
● The pt is asked to superimpose the indicator successively on each of the
fixation points,
● And the relative position of the eyes is plotted for each of these directions
of gaze
on a chart which is replica of the Hess screen.

21. Digital Hess
screen
● It is a new computer-based tool for assessing patients suffering from
paralytic strabismus, using image manipulation technology and
software technology.
● It is designed to run on any computer operating under Windows, with
a 19" (or
larger) monitor.
● When the program is run for the first time, the user is required to calibrate
the size of the screen (by measuring the dimensions of a box displayed on
the screen) and to enter the preferred viewing distance (usually 25-50 cm).
● It provides integration function of diagnosis of strabismus, data record and
analyze.

22. Key features
• Rapid and accurate assessment of the size and direction of phoria/tropia
• Results plotted in conventional Hess screen format allow the clinician to
establish
whether a deviation is concomitant or incomitant and which muscle is
affected.
• A variety of analytical tools to help the clinician form a diagnosis
• Built in database allows results to be archived for future reference
• Results can be printed or pasted into referral letters and reports
• Runs on a standard PC
• Voice instructions, possible.

23. Operating
methods
Steps of use are as below:
● • Patient wears red and green goggles and is positioned in front of the
computer
screen at the appropriate distance
● • Room lights are extinguished and a red and a blue circle are displayed on
the
screen
● initially the red circle is placed in the top left of the screen and the patient is
instructed to move the blue circle using the mouse until it appears to be
centred on the red circle.
● As the eyes are dissociated, any deviation in this direction of gaze will
result in a misalignment of the circles
● This is repeated for either 9 or 25 directions of gaze The colour of the
circles is then
reversed and measurements repeated with the left eye fixating. The nine

24. Lees screen
test
● Lees screen, also known as the Hess-Lees screen, is another modification of the
original Hess screen.
● The Hess-Lees screen consists of two tangent screens made of white translucent
material placed at a right angle with a plane mirror bisecting this right angle and
dissociating the fields of the two eyes.
● The tangent pattern similar to the original Hess screen printed in black dots
(fixation points) on a white background is placed just behind both the translucent
screens, and is seen only when the translucent screens are illuminated for
performing the test.

26. Lees screen
test
Procedure
● To perform the test with right eye fixing, the patient sits facing the left tangent
screen at 50 cm from it with his/her forehead leaning against the central vertical rim
of the mirror.
● The line bisecting the mirror horizontally lies in the same plane as the centre of the
horizontals of the tangent screens. Patient's pupils are levelled Lees screen.with this
horizontal line by an adjustable chin rest.
● The patient is given a pointer with a ring at its tip. The examiner has another pointer
with a small disc at its tip, half the diameter of the patient's pointer. The right screen
is illuminated and left screen is kept non-illuminated.
● The patient's right eye vision is intercepted by the mirror, in which he/she sees the
right
screen projected forward as a virtual image that appears to be superimposed upon
the left screen.
● The patient's left eye sees the left screen directly (he/she is facing that screen)
but cannot see the right screen, situated laterally..

27. CREDITS: This presentation template was
created by Slidesgo, and includes icons by
Flaticon, and infographics & images by
Freepik
Thanks
!