The document discusses various methods for measuring ocular deviations, including the cover test, prism bar test, Maddox rod test, and Maddox wing test. The cover test is described as the simplest and only objective way to distinguish between a phoria and tropia. It involves covering each eye and observing any movement in the uncovered eye. Alternative cover testing and prism bar testing can also help determine the size and direction of any deviation.

1. Measurement of Ocular Deviations

2. Heterophoria A deviation kept latent by the fusion reflex Prevent fusion to measure phoria Dissociation of the eyes required

3. Dissociation of Eyes Cover test Diplopia or displacement tests (vertical ∆) Distortion tests (Maddox Rod) Independent objects (Maddox Wing)

4. Cover Test Simplest method Objective assessment Used at any distance Only test to distinguish between phoria and tropia Use on ALL patients

5. Cover Test Patient fixates on smallest letter seen by poorest eye (eg R6/6 L6/12) Accommodative stimulus required Less than 6/18 use spot light Use an opaque occluder Don’t go too quickly

6. Cover Test Cover/uncover: allows diagnosis of phoria or tropia Alternate cover: allows size and direction to be determined

7. Alternative Cover Test Do not allow binocular fixation Move cover from one eye to the other If deviation present it will be seen as a re-fixation eye movement Will NOT distinguish between a phoria and a tropia

8. Cover/uncover Test Cover placed before 1 eye and then removed Observe the uncovered eye for movement; if movement is present then patient has a squint If a squint is present there cannot be a phoria

9. Strabismus: Cover Fixing Eye

10. Strabismus: Uncover

11. Strabismus: Cover deviating eye

12. Cover/uncover Test Observe occluded eye when covered; eye drifts out for XOP and in for SOP Observe occluded eye when cover removed; eye moves in for XOP and out for SOP

13. Phoria: SOP

14. Hering’s Law Innervation to synergist muscles of the 2 eyes is equal

15. Esophoria with Hering Response

16. Technique Ensure eye is completely covered At near move fixation target prior to cover to ensure fixation Observe latency and speed of recovery Estimate size Measure size using prism bar

17. Prism Cover Test

18. Prism Bar Base Out for SOP and SOT Base In for XOP and XOT

19. Displacement Test Vertical Prism

20. Distortion Test Maddox Rod Can be used for vertical and horizontal deviations

21. Maddox Rod

22. Maddox Rod Place rod before right eye Use spot light and dim room lights Ask “ is red line to the left or right of the spotlight?” If rod is to the right SOP If rod to the left XOP Use prism to align rod and spotlight

23. Maddox Rod

24. Esophoria

25. Esophoric Projection

26. Exophoria

27. Exophoric Projection

28. Maddox Rod

29. Independent Objects Maddox Wing

30. Summary Cover test only way to distinguish between phoria and tropia Perform on all patients with and without Rx Work in systematic manner Do not rush the diagnosis Use appropriate tets