Describe heterophoria with its symptoms and management.

Heterophoria

• Heterophoria is a latent deviation of the visual axes, held in check by the fusional reflex and revealed only when the eyes are dissociated.
• It is present in some degree in the great majority of the population and is asymptomatic.
• Types — esophoria (latent convergence), which is the commonest and is associated with hypermetropia; exophoria, associated with myopia and with convergence insufficiency; hyperphoria and hypophoria; and cyclophoria
• A small exophoria for near is physiological and needs no treatment; the question is never the presence of a phoria but whether it is compensated
• Decompensation occurs when the fusional reserve can no longer hold it, and is precipitated by ill health, fatigue, stress, alcohol, prolonged near work, an uncorrected refractive error and increasing age
• Symptoms of a decompensating phoria (asthenopia) — eye ache and brow ache after sustained near work; blurring that comes and goes; intermittent diplopia, particularly when tired; headache, characteristically frontal and worse at the end of the day; difficulty changing focus; and words running together when reading
• These patients are commonly told their eyes are normal, because acuity and fundi are unremarkable and the phoria is not looked for
• Assessment — the cover-uncover test shows NO movement (there is no manifest deviation), while the alternate cover test reveals the deviation as a recovery movement on uncovering. The speed and smoothness of that recovery measures the control.
• Also assessed — the MADDOX rod and Maddox wing for distance and near; fusional vergence amplitudes measured with a prism bar, which are the true test of reserve; the near point of convergence, normally within 10 cm; and stereoacuity
• Management, in order:
• 1. Correct the refractive error accurately — hypermetropia in esophoria, and full myopic correction in exophoria. This alone relieves many cases
• 2. Address the precipitant — working distance, lighting, screen position, breaks from near work, sleep and general health
• 3. Orthoptic exercises to build fusional reserves, which are particularly effective in convergence insufficiency exophoria — pencil push-ups, jump convergence and stereograms
• 4. Prisms incorporated into the spectacles for a persistent vertical phoria, or where exercises fail. The prism is under-corrected to leave some fusional work
• 5. Surgery only for a large, symptomatic and genuinely decompensating phoria that has failed everything else — and rarely
• Reassurance matters: these are anxious patients who have often been dismissed repeatedly, and explaining the mechanism is itself therapeutic