Clinical Skills Phorometry

Phorometry

the association of ocular alignment, its relationship to accomodation and how the one effects the other

phorometry measurments

use of occluders, prisms, maddox rids at varied distances

Binocular Vision

eyes in straight ahead position we can achieve binocularity and depth perception

in oder for binocular vision to occur, retinal images must have

Good focus

similar size

similar shape

aligned on the foveas of both eyes

Local sign

each point on the retina (rod or cone) has a specific "local sign"

local signs: when a point on the retina is stimulated it corresponds to the direction of the stimulus with respect to the

fovea

ex: when the inferior retina is stimulates , we know it was by the superior visual filed

Principal Visual Direction (local sign)

Foveally fixated spot is interpreted as being "straight ahead"

Corresponding retinal points

point on each retina, which when stimulated produce perception that are of identical direction

SEE IMAGE ON SLIDE 8

When non-corresponding retinal points are stimulated, the patient will have

double vision

diplopia

Corresponding retinal points send impulses to the ----- point on the visual cortex

SAME

ie the visual pathway

The visual pathway as an example of corresponding retinal points

The right visual field of each eye travels to the left visual cortex

the left visual field of each eye travels to the right visual cortex

Sensory Fusion

the images formed on the retina are combined into one single image

0

supression

1

simulataneous viewing/superimposition

Pt experiences diplopia or confusion

2

Flat fusion/luster (2)

2 similar targets form one percept, but no depth

3

Depth/stereopsis

ultimate sensory fusion

lateral displacement leads to depth

How to measure Sensory Fusion

Worth 4 dot - 0 to 2nd degree of sensory fusion

Stereopsis - 3rd degree of sensory fusion

Suppression

no binocularity

the patient is basically monocular

the brain's adaption to stop diplopia/confusion

Types of Suppression

Central (macular area)

Peripheral

Central (macular area) suppresion

response will vary at different distances

Measure suppression with Worth 4 dot

Suppress OD see 3 green dots

Suppress OS see 2 red dots

If a patient comes into the clinic saying they have double vision what test may you want to do

Worth 4 dot

tests 3 degrees of sensory fusion

Put red/ green glasses on pr

OD: red

OS: green

The instrument shows

1 red dot

2 green dots

1 white dot

Looking through OD

2 red dots

looking through OS

three green dots

both eyes working together

1 red dot

2 green

1 dot mixed

0 - 2nd degree of sensory fusion can be measured by

worth 4 dot

Causes of suppression

- constant strabismus (eye turn) - measure with cover test

- Decreased VA

- Monofixation syndrome/ microtropia

Decreased VA

Refractive error (aniseikonia/anisometropia)

media opacity (opacified cornea/lens)

retinal pathology (macular scar)

Aniseikonia

unequal image size

Anisometropia

unequal refractive error

Pt with suppression will

NOT have steropsis

When a patient has suppression cannot perform ____

binocular tests

binocular balance, Von Graefe phorias, vergences, Maddox rod

Panum's Fusion Area

A little 'wiggle room'

corresponding retinal points may not be exact, but sensory fusion is still maintained

Retinal Disparity

an object in space does not stimulate retinal points

patient will see double

for example, in a new eye turn or when prism is introduced in front of an eye

Retinal disparity is a stimulus for

motor fusion - use fusional vergences to align the eyes

Physiological diplopia

- large amounts of retinal disparity

- present in everyday life

REWACTH SLIDE 15 for finger example

Stereopsis

small amounts of lateral retinal disparity within panum's fusional area

allow fusion and forms a 3D image

REWATCH SLIDE 16

Eye movements are stimulated by

retinal disparity - diplopia

eye movements are necessary to establish

sensory fusion - binocularity/stereopsis

Types of eye movements

Conjugate

Disjunctive

Conjugate

eyes move in the same direction

saccades, versions (pursuits)

Disjunctive

eyes move in the opposite direction

vergences (convergene/divergece)

In Conjugate (versions) we use _____ muscles

yolked

if you look up and to the right

LR OD and MR OS are the yoked muscles

Saccadic movement

fast, abrupt

Pursuit movement

slow movements, keeping image on the fovea throughout the movement

Disjunctive (vergences): eyes move in different direction

Convergences: both eyes inward

Divergence: both eyes move outward

Vertical vergence: one eye up and the other down

Cyclovergence: eye rotate in opposite directions

Classification of Vergences (Maddox System)

Tonic Convergence

Accomodative Vergence

Proximal Convergence

Fusion Vergence

Tonic Convergence

determines the distance phoria

normal physiological tone to muscles

accomodative vergence

when you accomodate (focus) you also converge

Proximal Convergence

convergence due to the awareness of a near target

Fusion Vergence

compensates for phoria, brings images toward corresponding retinal points

Deviations

Heterophorias

Heterotropias

Heterophorias (latent deviations)

a.k.a phoria

only occurs under monocular conditions or when the eyes are dissociated (binocularity is prevented)

Heteropias (manifest deviation)

a.k.a tropias (strabismus)

occurs under binocular conditions

All patients have phorias or tropias at ---

any given time

Heterophoria are the

tendency of eyes to deviate from bifoveal fixation

resting position of the eyes when NOT under binocular conditions

Phorias are measure clinically by

interfering with binocular vision

Basic clinical process to measure phoria

occlude one eye (cover)

add prism to separate the images (Von grave )

present dissimilar targets to the eyes (Maddox rod)

fusional vergence movements are _____ when testing for phoria

prevented

Phorias are classified by

direction and magnitude

Orthophoria

When dissociated, eyes remain aligned

Exophoria

when dissociated, eye turn outward

Esophoria

when dissociated, eyes turn inward

Hyperphoria

When dissociated, one eye deviates upward

Hypophoria

when dissociated, one eye deviates downward

a hyperphoria of one eye is the equivalent to the ______ of the other eye

hypophoria

ALWAYS clincaaly record as

hyperphoria !!!!!!!!!

hypo for tropia but NOT PHORIA

Incyclophoria

when the tops of cornea rotate toward each other

Exocyclophoria

when the tops of the corneas rotate away from each other

Classifications of Tropias (under binocular conditions!)

Directions: position of the eyes

Frequency: How frequent is the tropia

Laterality: Which eye or both

Magnitude: How large is the deviation

Comitancy: is the amount of the deviation the same in different positions

Accommodative vs non - accommodative: deos accommodation contribute to deviation

Tropias may be reffered as an

eye turn

stabismus

tropia

lazy eye

Direction

Exotropia, Esotropia, Hyperrtopia, Hypotropia

hypo may be used in stabismus only

Frequency

Constant: all the time

Intermittent: Occurs some of the tome

Laterality

Unilateral: same eye deviates

Alternating: either eye will deviate

Magnitude

how many prism diopters in the deviation

Comitancy

(alternating cover test in 9 position of gaze)

Comitant or noncomitant

comitant

the angle of deviation (magnitide) remains the same in all positions of gaze within 5pd

noncomitant

the angle of deviation changes by more than 5 pd in different positions of gaze

If noncomitant

suggest a paresis, paralysis or mechainal restriction of EOMs

remember pursiuts (may have a deficit)

is there a motility deficit!

slide 28

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