W20 Classification of Eye Deviations

What does binocular vision depend on?

Motor and sensory fusion

What is motor fusion?

Fusional vergence moving the eyes from passive to active positions (small movements) so that visual axes are aligned to the ideation object

What is sensory fusion?

Perceptual fusion of the impulses from both eyes occurring in higher levels of the brain

What is dissociation?

Disrupting binocular vision- normal processes of fusion cannot take place

How do we dissociate the eye?

Using an occluder to block one eye- brain only receives monocular input so sensory fusion cannot take place

Why does fusional vergence not occur in dissociation?

Absence of retinal disparity abolishes the fusion reflex so fusional vergence does not occur

What position does the eye under the occluder take?

Its passive position- this is dictated by:

• Tonic vergence- if the other eye is fixating on a distant object

• Proximal and accommodative convergence- if the other eye is fixating on a near object

What is orthophoria?

NO deviation- eye under the cover will not move as passive and active positions coincide- fusional vergence is not required for bifoveal fixation- oculomotor balance is perfect

What are features of heterophoria?

• Latent deviation occurs when the eye is dissociated- active and passive positions do not coincide

• The dissociated eye will move to its passive position

• Fusional vergence is required for bifoveal fixation

• Oculomtor balance is not perfect, but adequate

How is the heterophoria deviation eliminated?

Motor fusion reflex eliminates the deviation when the obstacle to sensory fusion (cover) is removed

What is heterotropia?

Pathological misalignment of the eye (present without a cover in place)

Visual axes is misaligned (one eye fixates, one eye deviates)- fusion reflex has either failed to develop or is unable to function normally

How do we classify heterophoria?

According to direction, magnitude, fixation distance and compensation

What are horizontal heterophoria’s?

Esophoria and exophoria

What are features of exophoria? (XOP)

• Dissociated eye moves outwards

• Visual axes are divergent when eyes dissociated- px must need to converge extra to compensate

• Px has good positive fusional reserves to overcome phoria required for bifoveal fixation

What are features of esophoria? (SOP)

• Dissociated eye moves inwards

• Visual axes converge when eyes dissociated

• Px has good negative fusional reserves/divergence to overcome the phoria required for bifoveal fixation

What is hyperphoria?

Visual axes are vertically misaligned when eye dissociates

What type of hyperphoria can you have?

Left hyperphoria or right hyperphoria

What is right hyperphoria?

• If you cover the RE, it moves slightly upwards under the cover, if you cover the LE it moves slightly downwards- visual axes of RE is above LE

• Px must be good at infravergence to maintain binocular vision

What is left hyperphoria?

• If you cover the LE, the left eye will move up, if you cover the RE, the right eye will move downwards- visual axis of LE above that of RE

• Px must be good at supravergence

What is cyclophoria?

• Eyes rotate about visual axis when dissociated

• Incyclophoria- upper poles of corneae rotate nasally

• Excyclophoria- upper poles of corneae rotate temporally

How do we measure the magnitude of heterophorias?

Prism diopters (horizontal and vertical phorias), degrees (cyclophorias)

What are the typical range of values for fixation distance?

Distant measurements are approximately ortho, near measurements is reported to have physiological exophoria

What is basic heterophoria?

Distant phoria is equal to near phoria

What are exophoric deficiencys?

• Convergence insufficiency- N XOP is bigger than D XOP

• Divergence excess- D XOP is bigger than N XOP

What are esophoric deficiency’s?

• Convergence excess- N SOP is bigger than D SOP

• Divergence insufficiency- D SOP is bigger than N SOP

What is compensated heterophoria?

Adequate fusional reserves, no symptoms- MOST PHORIAS ARE COMPENSATED

What is uncompensated heterophoria?

Inadequate fusional reserves, may cause symptoms like asthenopia (eye strain)

What is a comitant deviation?

Deviation is constant in all directions of gaze

What is an incomitant deviation?

Deviation varies with direction of gaze, may be due to partial paralysis in origin/nerve supply supplying EOM

What are the different frequencies of tropias?

Constant or intermittent

What is a constant tropia?

Tropia is always present

What is an intermittent tropia?

Tropia is present some of the time, motor fusion can control tropia at certain times so it can become latent (heterotropia), may manifest with stress

What does laterality refer to?

Does it occur in one eye only (unilateral) or alternating eyes (alternating)

What is a unilateral tropia?

Px constantly fixates with the same eye, VA is often reduced in deviated eye- if this deviation develops in the critical period, this can cause amblyopia

What is alternating tropia?

Either eye can fixate- VA usually approximately equal in both eyes

What are the directions of different tropias?

• Esotropia- deviating eye is convergent (SOT) inwards

• Exotropia- deviating eye is divergent (XOT) outwards

• Hypertropia- deviating eye is elevated

• Hypotropia- deviating eye is depressed

What is the difference between incyclo T and encyclo T?

• Incyclotropia- upper pole of cornea in deviating eye rotated nasally

• Excyclotropia- upper pole of cornea in deviated eye rotated temporally

NO DIRECT TREATMENT EXISTS

What is basic heterotropia?

Distant tropia is equal to near tropia

What are exotropic deviations?

• Convergence insufficiency- N XOT is bigger than D XOT

• Divergence excess- D XOT is bigger than N XOT

What are esotropic deviations?

Convergence excess- N SOT is bigger than D SOT

Divergence insufficiency- D SOT is bigger than N SOT

What’s the age of onset of heterotropia?

• Congential- present at birth/ after few months (not as common)

• Acquired- onset during childhood/later in life (more common)

What is non-accommodative tropia?

Magnitude of tropia independent of amount of accommodation exerted

What is accommodative tropia?

Magnitude of tropia changes as accommodation exerted