Routine Screening Flashcards
Define heterophoria
Fusion free position is different to functional binocular position, therefore lines of sight no longer intersect at fixation target when fusion is eliminated.
Covered eye (CT) turns to regain bifoveal fixation.
Define orthophoria
Fusion free position and functional binocular position are identical
Define heterotropia
Visual axes do not intersect at fixation point. Axis of normal fixating eye passes through object of interest, but tropic eye does not.
Aka. strabismus
Congenital (poor development; amblyopia) or acquired.
Constant, intermittent, alternating
Unilateral CT
Detects oculomotor imbalance (P or T).
D @ 6m; N @ habitual WD (habitual Rx)
Target 1 line above best VA, “clear + single”
Cover placed over 1 eye (≥3s to dissociate fusion)
Tropia if uncovered eye moves to take up fixation
Repeat 3x
Alternating CT
Detects magnitude of deviation (P or T)
D @ 6m; N @ habitual WD (habitual Rx)
Target 1 line above best VA, “clear + single”
Cover alternated between eyes (≥1s per eye, ensure no fusion in between)
Phoria if any movement detected in either eye
Px reports if image moving with (exoP) or against (esoP) movement of occluder
Should you do alternating or unilateral CT first?
BOTH MUST BE PERFORMED.
Unilateral:
- potential ocular emergency with sudden onset T
- impossible to differentiate between T from P if alternating tested first (decompensated P can turn into T)
Alternating:
- smaller deviations, so easier to see
- indicates degree of compensation
CT + Prism Bar
Record minimum amount of prism required to neutralise movement of phoria/trophia.
Prism placed in front of either eye for P, in front of tropic eye for T.
Maddox Rod
Darkened room, fixation light target
Habitual Rx
Uses cylindrical rods of Maddox rod glass to distort retinal image of a point of light to a line
Fusion precluded due to no similar contours
Eyes adopt fusion free position (BE viewing diff images)
Prediction using cyclopean eye - crossed vs. uncrossed diplopia
Troubleshooting:
Unable to see both sim.: suppression, cover each eye, G filter before eye to reduce brightness difference between spot of light and line
Too many lines: scatter of light, choose brightest line
*if too many, unsuitable due to compromised accuracy
Problems: accommodation, peripheral fusion
@N: pen torch @ habitual WD
Von Graefe
Dissociating prism in front of 1 eye and Risley prism in front of the other
Target 6/12 line under normal room lights
Typically 6^BU R eye for H deviations and 10^BI L eye for V deviations
‘aligned like buttons on a shirt’ or ‘headlights on a car’
Poorest repeatability
Prentice Card
D @ 3m; N @ 33cm
Use of 6^BD in front of RE - blue exoP, yellow esoP
Maddox Wing
N only
Dissociation by septum, one eye views tangent scale, other eye sees arrow
Lower scale for cyclodeviations
Cons: scale figures too large to ensure accommodation, therefore may overestimate exo or underestimate eso, peripheral fusion possible
Can Px have a combination of P and T
At D or at N: no, they will have one or the other (or neither)
However, can have D tropia and N phoria (or vice versa).
What do we look for in a cover test?
Phoria vs. tropia
Direction of deviation
Magnitude of deviation
Speed of recovery of movement (smooth & quick vs. slow & jerky)
Use of bases to correct deviation…
BI = exoP BO = esoP
BU = lower eye (i.e. BU R/L = L hyperP) BD = higher eye (i.e. BD R/L = R hyperP)
Normative values for phoria
D: 0-2 XP
N: 0-6 XP
Define visual field.
The area of one’s surroundings that is visible at one time, with a steadily fixating eye.
Always tested monocularly
Normal VF
Sup 60deg
Inf 75 deg
Temp 100deg
Nasal 60deg
Amsler grid: indications, setting
Indications:
- useful for central scotoma/metamorphopsia
- central visual disturbance, unexplained dec. VA, macular pathologies
- quick, cheap, portable
- @ 30cm
- each square subtends 10degrees (grid 1deg)
- monocular
“Test for central vision. Can you see the central dot, is it clear & single? Whilst looking at the central dot can you see all 4 corners of the big square? Do any of the H/V lines appear blurring, missing, wavy or distorted?”
Amsler charts (1-7)
- Standard chart. Black background, 5mm square white grid, white central fixation target.
- Sim. to 1, but has 2 diagonal white lines to assist steady fixation for those with central scotoma
- Sim to 1, has red grid. Useful in toxic amblyopias and optic neuritis. Tests for malingerers with R and G filters.
- Scattered white dots with central white fixation target, oft. easier for Px to define specific or multiple central scotomas.
- White parallel lines only, central white fixation point. Orientation can be adjusted, useful for detection of metamorphopsia.
- Sim to 5, black lines on white card with additional lines 0.5deg above & below fixation.
- Sim to 1, but with additional 0.5deg in central 8deg. Used for subtle macular disease.
Confrontation
MUST BE PERFORMED ON ALL PATIENTS Testing peripheral vision (30-40deg either side) Useful for large, absolute scotomas. 9/10 postchiasmal defects 3/10 prechiasmal defects
Mandatory minimum evaluation to ensure Px meets driving licence requirement.
Setting:
- Eye level @ 75cm (hands 50cm away)
- Facial amsler first
- Each Q individually, both hands presented sim.
Neglect vs. Extinction
Neglect: Px keeps ‘neglecting’ 1Q
Extinction: Px gets correct with individual presentation of that Q
Which RS tests are compulsory?
VA
Confrontation
Cover test
Which RS tests are tested upon indication?
Amsler
Red cap testing
Perimetry
Colour vision (if not 1st time presentation)
Stereopsis (if not 1st time presentation)
Red cap testing
@40cm monocular
Comparison of brightness of red cap (1 to 10) in BE, noting any asymmetry
“Screening of the function of the optic nerve at the back of your eye that allows you to see”
Kinetic VF: tell me as soon as red cap changes colour/disappears
Comparison b/w Q: indicated if asymmetry
