Heterophoria and Fixation Disparity

what is a hetrophoria

latent misalignment of the eyes – in other words
it is only present when the eyes are dissociated

what is the average % of uk population with hetrophoria

20% in distance and 78% in near

what is duanes classification of exophorias

1. Convergence weakness – exophoria is greater at near than distance

2. Divergence excess – exophoria is greater at distance than near

3. Basic (non-specific) – little variation in size of deviation between distance and near

what is duanes classification of esophorias

1. Divergence weakness – esophoria is greater at distance than near

2. Convergence excess – esophoria is greater at near than distance  Linked to excess accommodative effort / accommodative spasm, high AC/A ratio, uncorrected hypermetropia, excessive proximal convergence or presbyopia. If severe can be CE esotropia.

3. Basic (non-specific) – esophoria does not vary much in size between distance and near

what are possible causes of vertical hyperphoria

• paresis of one of the elevator/depressor muscles

• Anatomical misalignments (e.g. muscle

insertion/globe displacement)

• Poor fitting glasses / anisometropia

• Grave’s disease

what are the risk factors for decompensation causing phorias

• Poor general health

• Change in occupation

• Fatigue

• Change in refractive error

• Anisometropia / anisekonia

• Stress

• Excessive close work

• Drugs / alcohol

• Increasing age

• Neurological disease

what is vergence amplitude

how much control they have on there phoria before they start seeing double

what is fixation disparity

a small misalignment of the eyes when you’re trying to focus on the same point, usually up close.

what tests are used for fixation disparity

mallet unit