Week 1.04 Visual Function & Comfort

Question 1

Why do we check BV?

Answer 1

1. Binocular coordination and cooperation contribute to visual function and comfort.
2. Provides an indication of patient health.

Question 2

Divergence excess XOP (XOT)

Answer 2

Exodeviation greater at distance than near

Question 3

Divergence insufficiency SOP (SOT)

Answer 3

Esodeviation greater at distance than near

Question 4

Convergence insufficiency XOP (or XOT)

Answer 4

Exodeviation much greater at near than distance
Often started >10prism due to physiological exo at near

Question 5

Convergence excess SOP (SOT)

Answer 5

Esodeviation greater at near than distance

Question 6

What is the prevalence of manifest deviations

Answer 6

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

Question 7

What are the parental influence on strabismus

Answer 7

• 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

Question 8

What has poor fusional ability got to do with strabismus

Answer 8

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.

Question 9

Uncorrected reafractive error types can be associated with what types of strabismus

Answer 9

Moderate hypermetropia —> accommodative SOT
Anisometropia —> amblyopia, suppression, microT
High congenital myopia —> SOT

Question 10

Which which conditions is there a higher incidence of strabismus present in children

Answer 10

• 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

Question 11

What is the aim of investigating deviations?

Answer 11

Refer medical or surgical
Optometric management - treatment via refractive modification, prisms, exercises

Question 12

Why intervene with deviations?

Answer 12

• cause in symptoms
• Likely to deteriorate if left untreated
• if the anomaly is a sign of ocular or systemic pathology

Question 13

What are the methods of investigation?

Answer 13

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

Question 14

What is the hirschberg test?

Answer 14

• 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

Question 15

Krimsky test

Answer 15

• use prism of increasing power in front of fixating eye to position control reflex symmetrically to deviated eye

Question 16

What is the only test to differentiate between a tropia and phoria

Answer 16

Cover test

Question 17

What does the alternative cover test not do?

Answer 17

Does not differentiate between phoria and tropia
Instead, it reveals total angle of deviation and confirms direction

Question 18

What is Herring’s law of innervation?

Answer 18

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

Question 19

Alternating tropia

Answer 19

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

Question 20

Intermittent tropia

Answer 20

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

Question 21

Prism diopters

Answer 21

Angle which corresponds to displacement of 1cm at 1m

E.g. 18cm line at 6m = 3prism diopters

Question 22

Which eye do we put the prism bar in a tropia and in phoria when doing the prism bar cover test

Answer 22

In a tropia - prism bar placed before deviating eye
In a phoria - any eye

Question 23

Which eye do we look at for vertical phorias

Answer 23

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

Question 24

Maddox rod

Answer 24

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

Question 25

Maddox wing

Answer 25

Room lights on
Px looks through the horizontal slits with both eyes (kinda like binoculars)
RE only sees arrows
LE only sees scales
Arrows positioned at zero on the scales but through the dissociation could be movement of arrow along the scales
Even numbers correspond to exophoria, odd numbers to esophoria

Question 26

Mallet unit (associated phoria)

Answer 26

Same rule if the eye which sees the nonissue strip deviated to one side of the x the deviation is the opposite
Let px see the target before you put on the visor (Polaroid filter) in place
Ask px if their perception is moving
Top red strip is seen by left eye and lower strip by the right eye