Week 1.04 Visual Function & Comfort Flashcards
Why do we check BV?
- Binocular coordination and cooperation contribute to visual function and comfort.
- Provides an indication of patient health.
Divergence excess XOP (XOT)
Exodeviation greater at distance than near
Divergence insufficiency SOP (SOT)
Esodeviation greater at distance than near
Convergence insufficiency XOP (or XOT)
Exodeviation much greater at near than distance
Often started >10prism due to physiological exo at near
Convergence excess SOP (SOT)
Esodeviation greater at near than distance
What is the prevalence of manifest deviations
Caucasians - 3-4%
More prevalent in girls
Black USA - 0.6%
ESO vs exo
Europe between 5:1 & 3:1
In japan exotropia is more prevalent
What are the parental influence on strabismus
• Increased risk of strabismus if either parent has it
• One parent 25-45% change, both parents 75-90% chance
• Advise parent to get child screened if family history of strabismus
• 60% of children with a strabismus have a close relative with it
• Unknown how transmitted, no it inherited but some factor that predisposes px is inheritance pattern probability multifactorial
What has poor fusional ability got to do with strabismus
If poor fusional ability exists then the influence of factors such as uncorrected hyperopia, anisometropia, trauma and illness may cause the eye to become strabismic
Loss of fusion in childhood generally leads to an esodeviation and in adulthood exodeviation
Differences due to differences in the tones of the muscles with age.
Uncorrected reafractive error types can be associated with what types of strabismus
Moderate hypermetropia —> accommodative SOT
Anisometropia —> amblyopia, suppression, microT
High congenital myopia —> SOT
Which which conditions is there a higher incidence of strabismus present in children
- Down syndrome
- Cerebral palsy
- Hydrocephalus
- Birth trauma
Depending on condition 40-60% of px present with strabismus
Higher incidence in children suffering from general disease such as heart lesions – have 4-6 higher frequency
Premature and low birth weight (2.5kg) children
What is the aim of investigating deviations?
Refer medical or surgical
Optometric management - treatment via refractive modification, prisms, exercises
Why intervene with deviations?
- cause in symptoms
- Likely to deteriorate if left untreated
- if the anomaly is a sign of ocular or systemic pathology
What are the methods of investigation?
Objective:
- General observation
- Hirshberg, Krimsky & bruckner tests
- cover test
Subjective:
- Diplopia or displacement tests e.g. Vertical prisms., complementary filters
- Distortion tests e.g. Maddox rod
- Tests with independent objects e.g. Maddox wing
What is the hirschberg test?
- Compares position of 1st purkinje image of two eyes formed by a pen torch
- Limited to testing at near
- Asymmetry of 1mm = 20prism diopters (problem)
- Need to consider angle
If corneal reflections displaced temporally - esodeviation
If corneal reflection is displaced nasally - exodeviation
Krimsky test
- use prism of increasing power in front of fixating eye to position control reflex symmetrically to deviated eye
What is the only test to differentiate between a tropia and phoria
Cover test
What does the alternative cover test not do?
Does not differentiate between phoria and tropia
Instead, it reveals total angle of deviation and confirms direction
What is Herring’s law of innervation?
Innervation of one eye is equal to the of the other eye, resulting in movement of the two eyes that are equal symmetrical and parallel
Alternating tropia
Eyes do not return when uncover eye
Fixation swaps to the other eye
Initial deviating eye now fixate and the initial fixating are now deviates
Swap cover to other eye and observe re-fixation when the cover is putting in place
Again, when uncover no movement back to where started
Intermittent tropia
Starts out with latent deviation that becomes manifest after cover
Need to look very carefully before and with first cover watch eyes when remove cover to see if fusion returns
Prism diopters
Angle which corresponds to displacement of 1cm at 1m
E.g. 18cm line at 6m = 3prism diopters
Which eye do we put the prism bar in a tropia and in phoria when doing the prism bar cover test
In a tropia - prism bar placed before deviating eye
In a phoria - any eye
Which eye do we look at for vertical phorias
Usually defined in terms of hypophoric eye
E.g. 3prism R HYPERp = 3prism L HYPOp but we use hyperphoric eye
Vertical phorias are less common than horizontal but more problematic
Maddox rod
Can put Maddox rod in front of either eye
Provide spotlight target at distance using the chart or hold pen light at near working distance. Dim room lights.
Ask PX to look at Spotlight and indicate if vertical red line is seen to the right or left of spotlight - this is horizontal. If runs straight through then no horizontal phoria
For horizontal phorias position grooves in Maddocks rod horizontally
For vertical phorias position grooves vertically
If MR in front of LE and px says streak is to left then that is esophoria - base out in front of RE apex in
If MR in front of RE, streak above spotlight then left hyperphoria (because right hypophoria)
Base down in front of left eye apex up
