Strabismus is a condition where the visual axes of the two eyes do not align at the point of fixation. It can be comitant, where the misalignment is consistent in all directions of gaze, or incomitant, where the deviation varies with gaze direction. A thorough assessment of strabismus involves testing visual acuity, refractive error, ocular alignment with cover tests and prism bars, ocular motility, binocular vision, and specialized tests like forced duction testing. The evaluation aims to determine the type and size of strabismus, assess binocular function, and identify any underlying causes.

1. Assessment of Strabismus
Dr. Arup krishna Choudhury
FCPS, DO, MBBS
vitreo-Retina Fellow (IIEI&H)

2. Strabismus is the condition when
visual axes of two eyes do not meet at
the point of fixation

3. • Comitant: Although misaligned they retain relation in all direction of
gaze
• Incomitant: Deviation is different in all position of gaze
• Tropia: It is manifest ocular misalignment
• Phoria: It is latent ocular deviation
• Alternate : Fixation is retained by alternate eye
• Unilateral: Only one eye habitually fixes
• Intermittent: when deviation remain only for some time

4. Tropia or Phoria can be
• Esotropia /phoria
• Exotropia/phoria
• Hypertropia/phoria
• Hypotropia/phoria
• Cyclotropia/phoria

5. Children at risk
• Consanguinity
• Positive family history
• Pre mature and LBW
• Smoking during pregnancy
• Chromosomal abnormalities - DRS
• Uncorrected refractive error
• Cerebral palsy

6. History
A careful history is important in the diagnosis
• Mother's Obstretical history
• Birth history
• Drug history
• Family history
• Developmental milestones
• Any trauma, especially to head or face

7. History..
• History of presenting complaints
• Age of onset
• Sudden or gradual
• Constant or intermittent
• Present for distant or near or both

8. History..
• Unilateral or alternating
• Is it present only when the patient is inattentive or fatigued
• Association with trauma or physical stress
• Old photographs
• History of previous therapy/Rx received
• General health

9. Examination
• Vision test
• Refraction
• Evaluation of strabismus
• Assessment of binocular vision
• Detailed ophthalmic evaluation
• Special test

10. Visual acuity
Preverbal children
• Fixation pattern
• Fixation behavior
• Preferential looking tests-
Teller acuity cards
Cardiff acuity cards
• OKN
• VEP

11. Visual acuity..
For 2-3 years
• Sheridan Gardner test
• Crowded kay picture test
• Coin test
• Miniature toy test

12. Visual acuity..
Preschool Children
• HOTV chart
• Lea symbols
• Allen figures

13. Visual acuity..
For school children and adults-
LogMAR
Snellen test type
E chart
Landolt’s test type

14. Refraction
• Refractive error may be
responsible for the symptoms of
the patient or for the deviation
itself.
• Preferably cycloplegic refraction

15. Strabismus evaluation
• Hirschberg test:
• Cover tests
• Corneal reflection test
• Subjective tests of ocular alignment
• Ocular motility

16. Hirschberg test:
Roughly 1mm shift signifies
7° or 15 prism diopter.

17. Cover tests
• Cover/uncover test
-one eye is covered and observe the movement of uncovered eye to
take up fixation
-position and movement of the covered eye, as the cover is removed

18. Cover tests..
• Alternate cover test
-one eye or the other is covered throughout the test;
- the movement of the covered eye is noted as the cover is changed
from one eye to the other

19. Cover tests..
• Cover-uncover test Alternate cover test
Phoria Total deviation
Tropia Eye preference

20. Information provided by the cover test
• Direction of the deviation
• Difference in the angle from near to distance fixation
• Effect of accommodation
• Patients refractive error
• Comitance or incomitance

21. Information provided by the cover test
• Characteristics of manifest strabismus; constant or intermittent;
unilateral or alternating
• Speed of recovery
• Presence of latent nystagmus

22. Recording results of the Cover test..
• Type of deviation; whether manifest or latent
• Direction of deviation ; Horizontal, vertical or combination of the two
• Which eye deviates
• Estimation of size
• Any special features ; incomitance, nystagmus, DVD

23. Prism cover test
• It combines the alternate cover test with prism
• Indication: measure the angle of total deviation
• Apex of the prism always placed towards the deviation

24. Prism cover test..
Technique:
• First alternate cover test performed
• Prism of increasing strength are placed in front of one eye
• Alternate cover test continuously performed
• As stronger prism are brought

25. Prism cover test..
• Amplitude of re-fixation movement gradually decrease
• At a point no movement is seeing
• Increased prism power until movement is in the opposite direction
• Then reduce prism power to find the neutral value.

26. Prism cover test..

27. Corneal reflex tests
Krimsky test:
• A prism bar is placed in
front of the fixating eye
• The power increased
• Until the reflections get
symmetrical.

28. Corneal reflex tests…
• Prism reflection test:
Involves placement of prisms in front of deviating eye
The power increased
Until the reflections are symmetrical

29. Subjective tests of ocular alignment

30. Maddox rod test:
Orthophoria: streak passes
through white light.
If streak passes on the left to
the light i.e. esophoria &, if
to the right then exophoria

31. Double maddox rod test:

32. MADDOX WING TEST:

33. Ocular motility
• Ductions: Monocular movement
• Versions: Binocular , simultaneous conjugate movement
• Vergences: Binocular, simultaneous, disjugate movement

34. Ocular motility..
• 9 position of gaze:

35. Ocular motility..
Information recorded must include:
• Whether movement is full, limited , or excessive
• Grade of abnormality,usually-4 to+4
• Direction of abnormality
• Any associated signs , like lid changes or presence of nytagmus

36. Ocular motility..
Grading of limitation and overaction:
• Limitation is usually graded on a scale of -1 to -4
• -4 indicate there is no movement beyond the midline
• -3 indicates that 25% movement remains,
• Over action is graded from +1 to +4

37. Ocular motility..
• Near point of convergence:
Nearest point on which eye can maintain binocular fixation.
Measured by RAF rule
It should be Less than 10 cm.
• Near point of accommodation:
Nearest point on which eyes can maintain clear focus.

38. Evaluation of BSV
3 grades
1. Simultaneous perception
2. Fusion
3. Stereopsis

39. Evaluation of BSV..
Aims of evaluation of binocular function
To determine if the aim of treatment should be restore
binocular single vision or to improve the patients appearance
and ensure that s/he has the best possible visual acuity

40. Evaluation of BSV..
Test for fusion
Base-out prism test

41. Evaluation of BSV..
Test for stereopsis
TNO test
Frisby test

42. Evaluation of BSV..
Lang test
Titmus test

43. Evaluation of BSV..
Test for sensory anomalies
Worth four-dot test Bagolini striated glasses test

44. Evaluation of BSV..
Synoptophore

45. Ophthalmic evaluation
• Anterior segment
• Pupils
• Intra-ocular pressure
• Fundus examination

46. Special test
• Diplopia charting
• Hess screen test
• Lees screen test
• PARK’S 3 step test
• Forced duction test

47. Diplopia chart
It is indicated in patients complaining of double vision

48. Hess chart:
Less screen:

49. PARK’S 3 step test:
• Use to identify cyclovertical muscle paralysis.
• Performed by measuring the vertical alignment in
1)primary position,
2) In right and left gaze and
3) In head tilt to the right and to the left.

50. Forced duction test:
Anesthetize the eye
Lids retracted
Patient looks in the direction of the muscle tested
Globe hold at the opposite limbus with forcep
Eye is rotated at the direction of action of muscle

51. Forced duction test:
Result:
• If free movement is present then the test is negative
• If restricted then the test is positive

52. Take Home message
• Time consuming
• Needs Patience specially for intermittent exotropia
For children
• Poor cooperation
• Lack of subjective response
Challenges