Assessment and Management of Strabismus

Fiona CrottyHead Orthoptist

East Sussex Hospitals

Overview

• Development of Visual Acuity• Assessment of Vision in Infants & children• What is BSV and how does it develop?• Classification of squint• Assessment of squint• Management of squint

Development of Visual Acuity

• Dependent upon normal anatomical and physiological development

• Eye relatively well developed in full-term infant– Shorter axial length (more hypermetropic)– Shallow anterior chamber– Poorly differentiated fovea (complete by 4

months age)– Accommodation 90% accurate by 2 – 3 months

Development of Visual acuity (VEP’s)

Age Visual Acuity

Newborn 6/240

1 month 6/180 – 6/90

4 -6 months 6/18 – 6/6

3 years 6/6*

* Tested with single optotypes

Assessment of Vision Birth to 12 months – forced choice preferential

looking

Assessment of vision 12 months – 2 years Cardiff Cards

Assessment of Vision - Cardiff Cards

Assessment of Vision – occluding glasses

Assessment of Vision2 – 4 years Kay Pictures

Assessment of Vision4 – 6 years Crowded logMAR

Assessment of Vision – LogMAR vs. Snellens Type

• Snellens:– Traditional method– 6 metre test distance– Recorded as fraction e.g.6/60, 6/9– Inconsistent numbers & spacing of letters per row

• logMAR:– Decimal value, 0.0 =6/6 equivalent, 0.2 = 6/9.5 etc– Equal number of letters per row, consistent spacing– Greater range of acuity values & can be used at 3m– Preferred method for research and amblyopia testing

Assessment of Vision

Snellens Chart logMAR Chart

What is BSV?

• Definition of Binocular Single Vision (BSV)– The ability to use both eyes simultaneously so that

each eye contributes to a common single perception

• 3 levels– Simultaneous perception ( 2 images seen)– Fusion (Interpreting 2 images as one)– Stereopsis (3-D appreciation)

Development of BSV

• Newborn reflexes present – essential for BSV development

• Require continued use and normal visual experience– Postural reflexes: static (head position to body)

and stato-kinetic (head relative to space)– Fixation reflexes: fixation (foveal) and re-fixation

(target to target and maintained to moving object)

Development of BSV

Most neonates show coarse re-fixation1.Conjugate fixation 1st to develop (eyes follow

object together)2.Disjugate fixation (follow approaching object –

convergence)3.Fusional reflex (correct for change in image

position)4.Kinetic reflex (controlled accommodation &

convergence)

Development of BSV

• From aet 4/52 Attempts at convergence seen • 5-6/52 conjugate fixing and brief following –

neonatal misalignment common• 4/12 saccadic eye movements develop,

neonatal misalignments reduce• 6/12 – 8/12 normal BSV established

Risk Factors for Development of Squint

• Prematurity• Neuro-developmental delay• Motor control disorders eg cerebral palsy• Refractive error, failure to emmetropise• Family history

(Brief) Classification of Squint

• Manifest (Heterotropia)– Esotropia (convergent)– Exotropia (divergent)– Vertical– Unilateral or alternating– Constant or intermittent (in Primary position, or in

certain positions of gaze)– Accommodative

(Brief) Classification of Squint

• Latent (Heterophoria)– Esophoria– Exophoria– Vertical ‘phoria– Fully compensated– Poorly compensated

Left Esotropia

Cover Test, Esotropia (1 & 2)

Pseudo Esotropia

Right Exotropia

Cover Test, Alternating exotropia (3)

Intermittent Squint Brown’s Syndrome

Intermittent SquintDuane’s Syndrome

Cover Test, Esophoria (4)

Cover Test, Exophoria (5)

Assessment of squint

• Visual Acuity• Cover Test• Ocular Movements• Convergence• Fusion/Stereopsis?• Measurement of angle (prisms)

Management of Squint

• Orthoptic assessment• Cycloplegic refraction & fundoscopy– Correct significant refractive error– Allow for refractive adaptation (up to 18/52)– Occlusion treatment for amblyopia (patches,

atropine)– Orthoptic exercises (intermittent deviations)– Surgery

Summary

• Early intermittent neonatal misalignment common between birth and 2-4 months

• BSV well established from 6 months• Sensitive period for development of vision and

binocular reflexes• Suspected squint after 4 months (corrected)

age should be referred for Orthoptic assessment

Acknowledgements

• Thank you to Manuel Saldana for his kind permission to use the video clips

Thank you