VF - Binocular Vision - Fusion and Heterophoria - Week 2 Flashcards
Describe how versions can be measured.
A semicircular frame is placed around the patient, and a point on the frame is moved, until they are unable to see/focus it.
They cant turn their head.
Describe the pushup method of convergence measurement.
Have them focus on a point in front of them. Bring it closer until they can no longer focus on it.
How does a prism bend light? How does this affect the eyes focus?
Light is bent towards the base, so the image appears closer to the apex. Eye must then shift to the apex to keep focus.
Define anatomical position of eyes at rest.
17 base beyond parallel.
They are divergent.
Define tonic vergence.
Position with normal innervation but no stimulus (in the dark)
Physiological position of rest
Define orthophoria.
If active and passive positons of the eye coincide.
Define heterophoria.
When the active and passive positions of the eye are different.
Name and describe the two kinds of heterophoria.
Exophoria
If the passive position is divergent to the active position.
Esophoria
If the passive position is convergent to the active position.
How can the angle of movement be detected?
Have a patient focus at distance, and cover one eye and observe movement.
Name 6 anatomical factors for heterophoria.
Size and shae of the orbit.
Anomalies of the muscles, sheaths, and ligaments.
Lesions of ocular motor neural apparatus.
Name 5 non-anatomical factors for heterophoria.
General fatigue
Overwork
Excessive use of alcohol/tobacco
Prismatic effect of spectacles
How common is heterophoria?
75-90% of general population is heterophoric.
Which meridian is the most common for heterophoria?
In the horizontal meridian.
Define hyperphoria, hypophoria, and cyclophoria.
Hyper/hypophoria - vertical misalignment
Cyclophoria - eye rotates about the visual axis. Rotation nasally - incyclophoria, temporal rotation - excyclophoria.
What fixation distances are used for distance and near phoria?
Distance - 6m
Near - 40cm
Is phoria consistent from far through near?
No, it differs at distance vs near.
Define physiological exophoria.
Normal exophoria occurring at near distances, relative to far distances.
Define compensated phoria and decompensated phoria.
Compensated - heterophoria is asymptomatic, fusional vergence maintains vergence
Decompensated - symptoms are apparent, correction may be needed
Name 9 causes of decompensated phoria.
- Excessive use of vision under demanding circumstances
- Inadequate fusion reserves
- Accommodative anomalies - uncorrected hyperopia
- Ametropia
- Poor general health
- Stress
- Old age
- Neurological disorders
- Side effects of medications
Name 9 symptoms of decompensated phoria.
Headaches Aching eyes Diplopia Blurred vision Focusing difficulties Difficult depth perception Monocular comfort over binocular Sore eyes General irritation
Name 7 ways of measuring heterophoria.
– Cover test – Maddox rod – Maddox wing – von Graefe’s method of insuperable prism – Prentice Card – Maddox double prism – Synoptophore
