The worse eye is usually the affected one (may be amblyopic)
It is easiest to estimate the script of spectacles by comparing the image of a line viewed through the lens and just around it. A distance line such as a doorway is perfect for this purpose.
Minus lens → “With” movement
Plus lens → “Against” movement
Ground in Prism
The image of the line through the lens has a fixed deviation away from the image of the line just around it. This cannot be compensated by moving the lens. The apex of the prism points towards the deviation.
Method for easy check: turn spectacles side-on
BO (CNVI palsy), BD (CNIV palsy on affected eye)
Shine a pen torch into the patient’s eyes and inspect the corneal reflexes. In patients with straight eyes, they should be symmetrical and lie over the same point on the cornea. In patients with strabismus, the corneal reflex of the fixing eye will lie centrally within the pupil, and the other will be displaced (1mm of corneal decentration = 15 Δ strabismus, Pupil margin = 30 Δ, Limbus = 90 Δ). Be aware that tropias can only be definitively diagnosed with cover testing. The Hirschberg test becomes more important when vision is poor (e.g. < 6 / 60 in either eye) and cover-testing is not possible.
Proptosis (axial vs. non-axial)
Nystagmus, facial asymmetry, hearing aids, scars (conjunctiva- squint surgery)
“Could this be TED?”- proptosis, chemosis, injection, lid retraction
Cover-test Distance (CTD) in Primary
Cover-test Near (CTN) in Primary
Either a fixation target or a pen torch may be used. A pen torch has the advantage that corneal reflexes can be viewed but some examiners don’t like this technique. Unlike cover testing for near, accommodation doesn’t have to be controlled. Gently hold your hand out near the patient’s chin or forehead (this “reminds” the patient to keep their head still) and make your movements slow but deliberate (avoid multiple passes). The upper eyelids may need to be elevated when the patient is in downgaze.
Grading and Documenting Ocular Rotations
A: Grade 0 is normal. For horizontal versions a grade of -4 indicates that the eye remains in primary when attempting to fully abduct or adduct.
B: When testing ocular movements at the extreme corners of gaze (at the ends of the “H”), +4 indicates overaction to vertical, -4 indicates underaction to horizontal).
C: The two eyes are drawn and points of gaze are graded.
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