8.1.2 Understands the management of a patient with an anomaly of binocular vision.

What is convergence insufficiency?

• BV disorder characterised by the inability of the eyes to work together efficiently when focusing on near objects.

  • Leads to inefficient near focusing and symptoms that worsen with prolonged close visual tasks.

• Common in school-age children, adolescents, and young adults.

  • Most cases are idiopathic with no obvious structural or neurological cause.

Convergence insufficiency

Clinical signs and investigation

• Near Point of Convergence

  • ≥6-10cm is deemed abnormal

• Cover Test

  • Exophoria will be greater at near than distance

• Stereopsis

  • May be a slight reduction but gross stereopsis may be intact

• Fusional Reserves

  • Reduce positive fusional vergence at near using Base Out prisms

Convergence insufficiency

Management

• Orthoptic exercises

• Prism glasses (Base In prism for symptom relief)

  • Often necessary in adults intolerant to therapy

• Correct refractive error (specifically hyperopia)

Give examples of Orthoptic Exercises

• Jump Convergence

• Pen to nose Convergence (Pencil push-ups)

• Dot card

• Stereogram card

Orthoptic Exercises

Jump Convergence

• Two targets are required one at near and the other at distance (at least 3m).

• Px should fixate on the near target close to break point of convergence, focus on it maintain single image then swap to distance target them back to near target ensuring its single and kept clear this should be repeated several times.

Orthoptic Exercises

Pen to nose Convergence (Pencil push-ups)

• Px holds small target at arm’s length while fixating slowly move the target closer at a consistent speed and attempt to maintain binocular single vision.

• If px reaches a point where binocular SV cannot be maintained even with effort then move away until made single again. When binocularity completely fails start from original position.

• Repeat 3-5 times (1-2 minutes with a break afterwards).

Orthoptic Exercises

Dot card

• Slim rectangular piece of card with single line in the middle the line carries equal spaced dots held to px nose at slightly depressed position.

• Px swaps fixation switching from one dot to the next starting furthest away slowly moving closer to the eyes maintaining a single image. Once px reach the end begin again for 3-5 cycles.

Orthoptic Exercises

Stereogram card

• Hold card at arms length. Introduce pencil between card and face.

• Slowly move the pencil towards your nose, keeping your focus on the tip. The four images will merge into three, with the middle image becoming complete and 3D (e.g., a full cat with ears, tail, and whiskers).

• Hold the single, clear, 3D image steady for a few seconds, then relax your eyes by looking into the distance or closing them.

What is Accommodative insufficiency?

• A non-strabismic binocular vision disorder characterised by a reduced amplitude of accommodation relative to age norms, leading to difficulty in sustaining clear near vision.

• Common in school-age children, adolescents, and young adults. Most cases are idiopathic with no obvious structural or neurological cause and detected due to high near task demand.

Accommodative insufficiency

Clinical signs and investigation

• Amplitude of accommodation

  • ≥2.00D below expected range

  • Hofstetter’s Formula: Average AA = 18.5 - (0.30 x age)

• Dynamic retinoscopy

  • High accommodative lag >0.75D

• Reduced accommodative facility

  • Normal is 11 cpm (monocular)

  • Normal is 8 cpm (binocular)

Accommodative insufficiency

Management

• Correct refractive error

• Accommodative jump with ±2.00D flippers

  • Monocular training first, then binocular integration

• Near Add

Managing heterophoria

Methods

• Removal of cause of decompensation

• Refractive correction

• Modifying prescription

What factors should be considered when managing heterophoria by removing the cause of decompensation?

• Long hours of close work

• Poor illumination or contrast

• Sudden increase in amount of close work

• Very close working distance

• Poor health

• Poor sensory fusion (unilateral cataract)

How does refractive correction help when managing heterophoria?

• Blur makes fusion more difficult, even a small rx can improve binocular fusion

• Anisometropia may produce inter ocular differences in accommodation required

How should the prescription be modified when managing heterophoria?

• Myopia and Esophoria - least possible minus for clear distance vision (minimise accommodative convergence)

• Myopia and Exophoria - most minus but minimum over correction (induce accommodative convergence)

• Hyperopia and Esophoria - max plus without causing blur (minimise accommodative convergence)

How is prism prescribed when managing heterophoria?

• Base IN for EXO deviations

• Base OUT for ESO deviations

• Always use the mallet unit to determine the strength of the aligning prism.

• This measurement is always less the than true prism value of the deviation via dissociation.

What other methods can be used when prescribing prism, and what should be considered regarding prism adaptation?

• Can also use prism which induce a quick and smooth recovery movement to alternating cover test.

• Prism adaptation may be required. Patients may struggle to adapt to prism when they are using the glasses at the distance the prism is not needed.

What is a Fresnel prism, and when is referral to another practitioner required?

Fresnel prism

Fresnel prism is a temporary, lightweight, adjustable method that allows for adaptation before committing to having prism incorporated into spectacles.

Referral to another practitioner

Required if there is a need for more BV expertise, px is uncommunicative, pathology related, head trauma linked, treatment to date within practice has not worked, sudden onset diplopia.

When is surgical management of strabismus considered?

Surgery is only considered when there is constant strabismus that is unlikely to resolve.

What are the indications for surgical management of strabismus?

• Infantile esotropia - early surgery improves stereopsis potential

• Acquired tropia

• Vertical strabismus

• Duane retraction syndrome, Brown syndrome

• Nerve palsies (after stabilisation)

What are the surgical goals of strabismus surgery?

• Reduce deviation angle so it is within fusional range

• Restore functional binocular vision

• Improve head posture

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