Binocular Vision Flashcards
NRA vs PRA?
Negative Relative Accommodation: how much the eye can relax at a fixed distance and keep object clear/single. add PLUS lenses. Normal value is +2.50. Over that, pt might have uncorrected or latent hyperopia or overminus.
Positive Relative Accommodation: how much the eye can stimulate accommodation to keep object clear/single at a fixed distance. add MINUS lenses. Normal value is -3-3.50. Over that, pt is over-stimulating accommodation, Less than that, pt doesn’t have enough accommodation.
Explain hyperopia and myopia in relation to plus power of the eye.
Cornea about +43D, Lens about +15D. Too much plus power is myopia (that’s why pt needs minus lens). Not enough plus power is hyperopia (that’s why pt needs plus lens)
What is accommodation?
Increase in plus power of the crystalline lens.
What is range of accommodation?
Distance b/n near point and far point. Far point is the furthest distance away where target is clear/single, accommodation is fully relaxed at this point. Near point is the closest distance to where target is clear/single.
What is the amplitude of accommodation?
A dioptric power. The difference b/n the amplitude at far point (zero) and near point (increasing).
What is lead of accommodation?
If accommodative response is more than the accommodative stimulus in a given distance. Eyes focus in front of the object.
What is lag of accommodation?
If accommodative response is less than the accommodative stimulus in a given distance. Eyes focus behind the object. +0.50 to +0.75 of lag at near is normal.
How do you measure AC/A ratio?
- Calculated: AC/A= IPD(cm) + 0.4m(Hn-Hf)
(Eso plus, exo minus) - Gradient: through -1.00
What is MEM? How does this test reflect both accommodative and binocular function?
Objective way to measure accommodative response. Any test performed under binocular conditions is affected by both. For ex, a finding of less plus may mean overaccommodation 2’ accommodative excess or high XP and decreased PFV.
