Vergences & Ocular Alignment Flashcards
What are vergence eye movements?
disconjugate eye movements to allow BSV at different distances
Describe the 4 types of vergence
Tonic: eye position in dark without visual input ~ midbrain neural activity keeps eyes straight
Accommodative: pupil constriction, near viewing (AC/A ratio)
Fusional & Proximal convergence
Explain the Accommodative Convergence/Accommodation (AC/A) ratio
change of phoria with accommodation, how much accommodative convergence exerted with 1D accommodation
usually 2/3:1 (vergences:accom)
How is AC/A ratio measured?
Response: vergence magnitude according to 1D accommodation change (optometer)
Stimulus: vergence magnitude according to 1D accommodative stimulus change
gradient of Maddox wing against lens accommodation
How is AC/A measured clinically?
Heterophoria method: change fixation target distance from infinity to 33cm
AC/A = PD + (prism NCT - prism DCT at 6m/accom. (1/f))
Gradient: phoria change/accommodation stimulus change
Describe the relationship between AC/A and age
ratio remains ~constant till 50ish then it reduces
less accom. / more exophorias
Describe abnormal AC/A and accommodation influence on ocular alignment
High ratio/accom. - over convergence at near (excess esophoria/tropia)
Low ratio/accom. - exophoria of convergence weakness
How is abnormal AC/A ratio treated?
+ relative convergence: + lenses, BO prisms treat exo, stereograms, reduce accommodation
- relative convergence: - lenses, BI prisms treat eso, stereograms (distal pen) reduce convergence
How do cycloplegics affect AC/A ratio?
increases it as cycloplegia decreases accommodation but is reversible
near objects seem small in cyclo, higher convergence/less accom.
eso: high AC/A want to pull eyes out keeping accom.
exo: pull eyes in, need convergence
Explain fusion/motor vergences and how they maintain ocular alignment
Fusional: foveae aligned in binocular viewing or sensory fusion/stereopsis is impaired
under dissociation eyes assume fusion free position creating disparity/phorias ~ brain detects and fixates eye via vergences
How is fusional vergence measured?
Prism Fusion Range for near/dist. and +BO/-BI
Px with specs fixates on accommodative target
Increase prism till break point (diplopia)
Decrease again till recovery point (BSV regained)
Fusion is value before break point
What do blur, break, and recovery points represent in PFR?
Blur: limit of +BO/-BI relative convergence
BP: limit of motor fusion, foveal fixation loss/diplopia
RP: motor fusion restores fixation
What is a positive/negative fusional reserve?
maximum amount eyes can
+ve: converge to gain fixation (BO)
-ve: diverge (BI)
Which fusional reserve range should you measure first?
esophoria: BI 1st
exophoria: BO 1st
How are PFR results interpreted and which factors affect them?
compare +/- reserves, amplitude deviation from normal, break/recovery points
influenced by fixation targets (small may elicit earlier blur point), instructions for px, types of prism, rate of change in prism
