Binocular vision - easier than you think (lecture) Flashcards
(21 cards)
The two system approach
Vergence (aiming) system
Accommodation (focusing) system
Binocular metaphor for patients to explain two systems
You have to line binoculars up in front of your eyes and then you have to adjust the focus.
In a similar way, we have muscles outside of our eyes that help line our eyes up to point at the object of interest (our vergence system) and muscles inside of our eyes to help adjust the focus to make things clear (our accommodative system).
What 3 things do both systems need
- Stamina
- Stability
- Maintenance without fatigue
Diagnoses for underactive vs overactive vergence
Underactive: exophoria or convergence insufficiency
Overactive: esophoria or convergence excess
Both: infacility/ spasm
Diagnoses for underactive vs overactive accommodation
Underactive: problems with minus or accommodative insufficiency
Overactive: problems with plus or accommodative excess
Both: Infacility/ spasm
Most binocular vision problems occur where?
Near- where kids spend most of their time reading/ where adults spend most of their time working.
Distance binocular problems aren’t as much of an issue.
“Normal” ranges for near phoria
1 eso - 4 exo
“Normal” base out fusional range for near (based on jump vergence not smooth vergence when testing with prism bar)
30/25 (break/recovery)
“Normal” base in fusional range for near (based on jump vergence not smooth vergence when testing with prism bar)
12/10 (break/recovery)
“Normal” NPC (jump)
10cm, held
“Normal” accommodation range
Normal NRA: clears -3.50
Normal PRA: clears +2.00
Cycles on +/- 2.00
“Normal” AC/A ratio
accommodative convergence/ accommodation (the amount of convergence measured in prism diopters per diopter change in accommodation)
3:1
“Exo problems”
- Distance & Near: Basic Exo
- Near: Convergence Insufficiency
- Distance: Divergence Excess
“Eso Problems”
- Distance & Near: Basic Eso
- Near: Convergence Excess
- Distance: Divergence Insufficiency
Explain “twice as much petrol in the tank to balance the posture”
The numbers for their fusional ranges need to be double the number of their phoria to balance it out.
With the prism bar, what do you always want to measure first?
Divergence first, then convergence
NRA or PRA first?
Plus first before minus
Vergence disorders involving both eso & exo
Infacility: mainly at near, low positive fusional ranges (BO) and negative fusional ranges (BI)
Inflexibility/ spasm: fatigue or persistence of effects “sticky eyes”
Common co-occuring vergence & accommodation diagnoses
Accommodative insufficiency and convergence excess (concern for myopia development and progression)
Accommodative excess and convergence insufficiency.
Difficulties diverging often goes hand in hand with
Low PRA (testing how well someone can clear minus, putting the plane of vergence behind the plane of accommodation)
Difficulties converging often goes hand in hand with
Low NRA (testing how well someone can clear plus, putting the plane of accommodation behind the plane of vergence)
