Day 11 (3): Basic Motility and Vision Examination Flashcards
What is Normal Retinal Correspondence?
- describes the normal binocular relationship of the eyes in which TRUE anatomic foveas are linked together in the cortical area
- images which fall roughly on the same retinal areas relative to the fovea (CORRESPONDING AREAS) are perceived as lying in the same visual direction
- patient uses the real fovea to be able to fuse a single image
- present when stimulation of corresponding retinal points produce SINGLE vision
What is Anomalous Retinal Correspondence?
- an ADAPTATION mechanism IMMATURE visual systems to prevent diplopia
- adaptation of the brain to a SMALL-angle strabismus wherein the brain uses a PSEUDOfovea on one eye superimposed with the true fovea on the other eye to fuse an image
- eye’s attempt to regain binocularity and stereopsis
- (+) fusion inspite of a manifest misalignment
- present ONLY in BInocular conditions: when the fixating eye is occluded (monocular condition), the deviated eye would shift back to using its true anatomic fovea
- present when:
- stimulation of corresponding retinal points produce diplopia, OR
- stimulation of disparate retinal points produce single vision
What are the two types of ARC?
Amblyoscope:
- Angle of Anomaly NOT ZERO
- Objective angle NOT = Subjective angle
- image superimposition DOES NOT happen at the true foveas [O not = S] thus (+) PSEUDOfovea [AoA not = 0]
Harmonious ARC
- superimposition occurs with Subjective angle at ZERO
- Angle of Anomaly = Objective angle of Deviation
- indicates that the ARC fully corresponds to the strabismus
- distance of the pseudofovea from the true fovea EQUAL angle of deviation
- images are still fusible even if the eye is deviated thus awareness of diplopia and confusion is eliminated
Unharmonious ARC
- superimposition occurs with SUBJECTIVE angle BETWEEN zero and objective angle
- Angle of anomaly < Objective angle of Deviation
- distance of the pseudofovea from the true fovea NOT EQUAL angle of deviation
- images are not fusible thus (+) diplopia or (+) suppression
What is Eccentric Fixation?
- failure of an eye in MONOcular vision to take up fixation with the fovea, instead using an EXTRAfoveal point
- when the fixating eye is occluded, deviated eye will still use the extrafoveal area
- NO fusion: poor vision and diplopia
- hardly occurs except in clinical conditions as the patient is generally not fixating with the affected eye anyway
- present in BOTH monocular and binocular conditions
vs NH-ARC:
- present ONLY in BInocular conditions
- when fixating eye is occluded, deviated eye shifts back to the TRUE fovea
What is Monofixation Syndrome?
- unilateral macular scotoma (central suppression)
- INTACT peripheral fusion
- due to small-angle deviations (< 8 PD)
Causes:
1. unilateral macular lesion
2. inability to fuse single macular images
3. anisometropia: unequal EoR
4. surgical treatment for large-angle strabismus (> 10 PD)
What is Angle Kappa?
- angle between the VISUAL AXIS (line connecting the fixation point with the fovea) and the PUPILLARY AXIS (line that perpendicularly passes through the pupil and the center of curvature of the cornea
- identified clinically by the NASAL displacement of the corneal light reflex from the pupil center
- represents a misalignment of light passing through the refractive surface of the cornea and the bundle of light formed by the pupil
- as the fovea lies slightly temporal to the point at which the pupillary axis intersects with the posterior pole of the globe, the NORMAL angle kappa is SLIGHTLY POSITIVE
- causes PSEUDOstrabismus as a COMPENSATORY mechanism to align the visual axis to the pupillary axis
POSITIVE AK
- EXOtropic-like pseudostrabismus
- true fovea is TEMPORAL to the point at which the pupillary axis intersects with the posterior pole of the globe
- in order to align both points, the eye needs to ABDUCT (rotate TEMPORALLY) to move the fovea nasally
- CLR: found nasally
NEGATIVE AK
- ESOtropic-like pseudostrabismus
- true fovea is NASAL to the point at which the pupillary axis intersects with the posterior pole of the globe
- in order to align both points, the eye needs to ADDUCT (rotate NASALLY) to move the fovea temporally
- CLR: found temporally
Differentiate Phoria from Tropia.
HeteroPHORIA
- latent/unmanifested deviation
- exist in MONOcular conditions ONLY: deviation does not manifest until binocularity is disrupted
- present sometimes and may disappear
- Esophoria: nasal deviation (adducted)
- Exophoria: temporal deviation (abducted)
- Hyperphoria: superior deviation (elevated)
- Hypophoria: inferior deviation (depressed)
- Orthophoria: NO deviation
HeteroTROPIA
- manifest/unmasked deviation
- exist in BInocular conditions: deviation is grossly seen even without disruption of fusion
- present all the time
- Esotropia: nasal deviation (adducted)
- Exotropia: temporal deviation (abducted)
- Hypertropia: superior deviation (elevated)
- Hypotropia: inferior deviation (depressed)
What should be the first part of the examination of the patient?
OBSERVATION
- begins as soon as the patient enters the room
- especially for children who will start crying once examined closely
- Lid Fissures: unequal fissures, ptosis
- Globe position: wide intercanthal spaces, facial asymmetry
- Manifest deviations (Tropias)
- Head postures
- (+) nystagmus: turn head OPPOSITE the side of the nystagmus where there is LEAST movement
- (+) diplopia: turn head TOWARDS direction with the LEAST doubling of vision
- (+) paretic eye: head turned TOWARDS paretic eye to shift focus back to true fovea
- (+) uncorrected EoR, astigmatism
- (+) stiff sternocleidomastoid
- (+) hearing anomalies
What are the different sensory examinations done to assess strabismus?
- used to check for binocular fusion: ability to fuse two images viewed with both eyes
- done BEFORE disruption of binocularity with VA tests and cover-uncover test
- wear proper correction to get BCVA
- Stereopsis test
- Titmus Fly Test
- Lang Stereotest
- Frisby Stereotest - Worth 4-Dot test
- Bagolini Striated Glasses test
- 4-PD Base Out Prism test
What is stereopsis?
- DEPTH perception: HIGHEST form of binocular fusion
- ability of the eyes to fuse images that simultaneously fall on DISPARATE retinal areas BUT within the Panum’s area, resulting in 3D perception
- major contributor to depth perception obtained through binocular vision
- due to horizontal/binocular disparities: each eye receives a different image due to slightly different positions on one’s head
- perceived depth INCREASES with INCREASING disparity but TOO MUCH disparity will eventually cause loss in stereopsis leading to DIPLOPIA
- good stereopsis indicates brain’s ability to fuse images and recognize depth
Tests for Stereopsis
- (+) gross stereopsis = good binocularity = NO need to do other sensory tests
- Titmus Fly test
- Lang Stereotest
- Frisby Stereotest
What is the Titmus Fly test?
- uses polarized glasses similar to 3D glasses to see depth
- used to assess stereopsis in children
- pt is asked to pinch the wings of the fly while wearing the glasses
Results:
- pinch mid-air: (+) stereopsis
- pinch or finger flat on the paper: (-) stereopsis
What is the Lang Stereotest?
- based on random dot patterns
- polarized glasses not needed to perform test
- assess stereopsis in as young as 6 months
- separate images are provided to each eye
- series of images are presented with gradually smaller disparity
- the smaller the disparity identified, the better the stereoacuity grading
What is the Frisby Stereotest?
- presents real depth objects viewed with natural vision
- each plate has four random-pattern squares with a circle of pattern elements lying in depth relative to its surround
- depth effect is due to circle and surround being printed on opposite sides of the plate
- has 3 plates allowing for testing stereo acuity disparity as fine as 15 seconds of arc
What is the Worth 4-Dot Test?
- done in COOPERATIVE patients and even young children
- tests for motor fusion and to identify suppression
- patient is shown 4 dots:
+ Upper dot: Red
+ Lower dot: White
+ Horizontal dots: Green
Set-up:
1. Left eye: Green glass
- blocks red color
- sees the two green dots and one white dot
2. Right eye: Red glass
- blocks green color
- sees the one red dot and one white dot
3. Testing distance
- NEAR: 1 feet (for peripheral fusion)
- DISTANCE: 6 meters (for central fusion)
Results:
1. 4 Dots: NRC (Orthophoric) or ARC (Strabismus)
- white dot can be green, red or pink
- 5 Dots: (+) Diplopia
- 2 Red Dots (upper and lower dot)
- (+) Left suppression - 3 Green Dots (horizontal and lower dot)
- (+) Right suppression
Special circumstance: Monofixation Syndrome
- (+) CENTRAL suppression
- intact PERIPHERAL fusion
- manifests only at FAR testing distances (6 m)
FAR testing distance (6 m)
- testing angle is WITHIN the angle of the suppression scotoma
- 2 Red Dots: Left suppression
- 3 Green Dots: Right suppression
NEAR testing distances
- testing angle is OUTSIDE the angle of the suppression scotoma
- 4 Dots (1 Red, 2 Green, 1 Any)
What is the Bagolini Striated Glasses Test?
- done in COOPERATIVE, OLDER patients because they need to properly describe what they see
- tests for retinal correspondence and to identify suppression
- test most likely to allow the demonstration of fusion in patients who fuse intermittently
- (+) ARC: Binocular Single Vision (BSV) BUT with a strabismus on cover test
Set-up:
1. Patient is asked to wear glasses with angulated striations:
+ Left eye: 45 degree striations (line: )
+ Right eye: 135 degree striations (line: /)
2. Testing distance: 6 meters
3. Lights ON
Questions:
Ask how many LIGHT POINTS are seen:
- TWO: Diplopia (Crossed vs Uncrossed)
- ONE: BSV or Total Suppression
–> Ask how many LINES are seen:
- ONE: TOTAL Suppression
- TWO: BSV
–> Ask if lines are COMPLETE:
- Complete: No suppression/scotoma
- Incomplete: Central (Monofixation) or Peripheral (Scotoma)
–> Do Cover Test if BSV:
- if (-) shift: Orthophoric + NRC
- if (+) shift: Strabismus + ARC
Results:
1. Complete X: BSV
- see a cross with ONE light point in the middle
- means fusion is intact
- do cover test to differentiate NRC from ARC
- Incomplete X
- BSV/fusion intact since (+) X but with a gap
- the line with the gap corresponds to the eye with the suppression or scotoma
- remember to always confirm if the lines seen are complete or with gaps
A. Monofixation Syndrome
- central suppression + intact peripheral fusion
- gap is centrally located
- due to small deviations (< 8 PD)
B. Peripheral Scotoma
- gap is peripherally located
- due to larger deviations (> 10 PD)
- larger shift = larger scotoma = larger gap
- Entire line missing: (+) Total Suppression
- /: Left suppression
- : Right suppression - CROSSED diplopia: EXOTROPIA
- see TWO light points
- light point of L crosses to the R while that of R crosses to the L because
- because eye is ABDUCTED, object point falls on the TEMPORAL hemiretina
- this is interpreted by the brain as coming from the NASAL visual field thus line appears to move more NASALLY - UNCROSSED diplopia: ESOTROPIA
- see TWO light points
- light point of L remains to the L while that of R remains to the R
- because eye is ADDUCTED, object point falls on the NASAL hemiretina
- this is interpreted by the brain as coming from the TEMPORAL visual field thus line appears to move more TEMPORALLY - Hypotropia:
- object point falls on INFERIOR retina responsible for SUPERIOR visual field
- LEFT: \ higher than /
- RIGHT: / higher than \ - Hypertropia:
- object point falls on SUPERIOR retina responsible for INFERIOR visual field
- LEFT: \ lower than /
- RIGHT: / lower than \
Differentiate ESOtropia from EXOtropia.
ESOtropia
- Convergent squint: eye moves nasally or inward
- instead of focusing on the fovea, light falls on the NASAL RETINA which corresponds to the TEMPORAL FIELD
- two UNCROSSED images will be seen:
+ fixating eye: central fixation point
+ esotropic eye: TEMPORALLY-displaced
EXOtropia
- Divergent squint: eye moves temporally or outward
- instead of focusing on the fovea, light falls on the TEMPORAL RETINA which corresponds to the NASAL FIELD
- two CROSSED images will be seen:
+ fixating eye: central fixation point
+ exotropic eye: NASALLY-displaced
What is Hering’s Law of Reciprocal Innervation?
- Isolated innervations to an EOM do NOT occur nor can the muscles from one eye be innervated alone
- to perform an eye movement (cardinal gaze), impulses are always integrated between YOLK muscles
- yolk muscles of each eye receive EQUAL and SIMULTANEOUS innervation to perform a cardinal gaze movement
E.g. Levoversion or Left gaze
- LLR and RMR receive equal innervation to turn both eyes towards the left side
What is the 4-PD Base Out Test?
Note: Prisms bend light TOWARDS base
- used to determine if the patient has sensory fusion or a small suppression scotoma
- objective screening test to check for foveal suppression especially in patients with microtropia (small-angle strabismus)
- done under BInocular conditions
Steps:
1. 4 PD prism is held BASE OUT in front of one eye while the patient fixates on a target.
2. Look for any biphasic movements on the fellow eye.
How does it work?
- a BASE OUT prism displaces the light entering the eye TOWARDS the base or TEMPORALLY at the temporal retina
- to compensate, the eye needs to ADDUCT or move inwards to move the fovea temporally where the light falls
- Hering’s Law: adduction of ipsilateral eye via MR causes abduction of the contralateral eye via LR to maintain proper gaze position
- if the fellow eye is normal, it will display biphasic movements:
Phase 1: Abduction due to Hering’s Law
- causes fovea to move nasally thus entering light will fall on the TEMPORAL retina
Phase 2: Corrective adduction
- to fixate properly, fellow eye needs to adduct back to normal position to use its fovea
- failure of this phase will cause diplopia
What happens in ARC?
- true fovea of the fixating eye already corresponds with a pseudofovea in the deviated eye
- even when a prism is in front of the normal eye, (+) BSV but will NOT display corrective adduction and will remain deviated
What is the purpose of obtaining visual acuity in strabismus cases?
Purpose:
1. Determine baseline vision
2. Gauge improvement, stability or worsening of vision after ophthalmic intervention
- Done once all necessary sensory tests are performed because this will involve disrupting the pt’s binocularity
How is visual acuity defined in the different patient age groups?
Cooperative and Verbal or Literate
- measures the ability to resolve details
- discern a target of ever decreasing size from a given distance
Uncooperative, Pre-Verbal or Illiterate
- assesses the sensory and motor responses to a stimulus at varied distances and locations
- motor responses are used to gauge a sensory function
- problem: absence of a response could be due to a problem in the efferent (oculomotor) pathway and not in the afferent (optic nerve) pathway
2 Types:
1. Indirect Vision Assessment
- used in toddlers or infants with whom vision comparison between the 2 eyes is more important than getting the quantitative VA of each eye
- Resolution Acuity Tests
- measurable and quantifiable tests for older but pre-verbal or pre-literate children
