Accommodation Flashcards
What is accommodation?
Changes in refractive power of the crystalline lens to allow clear vision over a range of distances
What happens during accommodation?
Ciliary muscle contracts and pulls choroid forward, zonules relax, lens becomes more convex
Why does accommodation decrease over time?
The lens becomes less flexible
How can we study the development of accommodation?
Retinoscopy, measure eyes; focal distance to stimulus distance aka accommodative error
When is accommodation accurate?
8-9 weeks old
T/F photorefraction estimates optical errors and accommodation
False, does not estimate accommodation
What did the Braddock study find about infant focus at two distances?
Infants see up close (75 cm) first and distance (150 cm) afterwards, both distances are 100% at 6-8 months
When does an accurate accommodative response develop?
At 2-3 months
Why do infants < 3 months old tend to over accommodate?
Target proximity, large depth of field, poor sympathetic innervation to ciliary muscle to relax accommodation
How can you test accommodation in infants/toddlers/school aged?
Near dynamic retinoscopy
How can you test accommodation in school aged children?
Amplitude of accommodation, FCC, near ret, NRA/PRA
What are the amplitude of accommodation methods?
Push up, pull away, minus lens all subjective and monocular
T/F you can test amps uncorrected
FALSE
Which amp of accommodation method is more accurate?
Push up slightly more accurate than pull away at least
What is the procedure for minus lens amp of accommodation?
In phoropter, use 1 line above best VA at 40 cm, add minus lenses until patient reports first slight sustained blur
Where do you have to start with young children on the minus lens procedure?
-3.00 over Rx since they have a large amount of accommodation
How do you calculate the amp of accommodation in a minus lens test?
Take the diopter power from lenses at first sustained blur and add working distance for the 40 cm (2.5 D) or even 30 cm and 3 D
What is the average amp according to Hofstetter?
18.5-1/3(age)
What is the minimum amplitude according to hofstetter?
15-1/4(age)
What does the Swedish study say about hofstetter norms?
They are overestimated by 2 D, new standard would be hofstetter - 2
What is the purpose of NRA/PRA?
To measure fusional convergence and divergence, also looks at accommodation
How do you perform PRA?
Minus lenses OU with convergence set at 40 cm, maintain single and clear vision, lenses will increase accommodative convergence
How do you perform NRA?
Add plus lenses OU, convergence set at 40 cm, maintain single and clear vision, relax accommodation, will decrease accommodative convergence
What is a normal NRA value?
+2.00
What is a normal PRA value?
-2.37
What is the Harmon distance?
Comfortable reading distance, “middle knuckle on fist to elbow”
Where does one focus with the ideal lag of accommodation?
Behind the target
What is the purpose of FCC?
To determine the lag of accommodation or add subjectively
What is the FCC procedure?
FCC card, +/- 0.50 lenses, see which lines are darker
If the horizontal lines are darker in FCC what does that mean?
Lag of accommodation, add plus lenses until patient reports the lines are clear
What does it mean in the vertical lines are darker for FCC?
Lead of accommodation
What is the expected FCC result?
+0.25 to +0.75
What is the purpose of near ret?
To determine the need for a near vision correction/add over the distance Rx
Is near ret objective or subjective?
Objective
What is the objective equivalent to FCC?
MEM/Nott
What is the goal of streak ret?
Neutrality and finding astigmatism axis
What is the goal of spot ret?
Allows more light from retina, better color, brightness, and you can observe 2 meridians simultaneously
What equipment is needed for MEM?
MEM Cards, Ret, looses lenses, current Rx
What is the procedure for MEM?
Perform at Harmon’s distance or 16 inches while patient reads words on appropriate reading level cards with both eyes open wearing appropriate Rx, examiner estimates the dioptric value of motion and dips lenses in front of the eye for 1/5th of a second
What is expected from MEM?
+0.25 to +0.75
What is a concern for MEM?
Unequal reflexes, lag >+0.75, against motion
How do you Rx for near after MEM?
Add plus spheres binocularly until MEM results within expected values
If there is against motion on MEM do you add minus lenses?
NO
What equipment do you need for bell retinoscopy?
Wolff wand, ret, yard stick or measuring tape, probe lenses
What is the procedure for bell ret?
Patient wears Rx, start with target and ret at 20 in/50cm then move target closer, then move target away from patient
What should you observe on bell retinoscopy?
With motion that decreases until neutral then against motion as accommodation localized closer than the ret, once the target is moved further away, will see with motion again
T/F bell retinoscopy uses lenses?
False, it uses different target distances
How do you record bell ret results?
As a fraction of the range of neutrality ex: 15/16 which means w/ to against and then back to with and is recorded in inches
What do you do if the bell ret is abnormal?
Recheck with probe lenses, if against and check with probe is still against there is no further testing
What does bell ret compare?
Accommodative response to accommodative stimulus (distance from ret to patient and distance from target to patient)
T/F on bell ret, when there is a neutral reflex, accommodation is at the plane of the retinoscope
True
What is the difference between AR and AS?
The lag
What is expected for bell retinoscopy?
17-14 in with to against/16-18 inches against to with
What equipment is needed for book ret?
Book, ret, probe lenses
What is the procedure for book ret?
While patient reads with appropriate Rx, observe the reflex in each eye on the same passage looking for motion, color, brightness, symmetry
What reading level should the book be?
Start with easy material at least 2 grade levels below then move to more difficult things
T/F changes in color, brightness and motion are associated with cognitive demand and interest
True
What should you observe on book ret during free reading (desired)?
Whitish pink color, bright, neutral to low width motion (+0.50), little cognitive effort needed
What should you observe with easy instructional reading for book ret?
Pink, bright, with to against (-0.25 to +0.75), some cognitive effort
What should you observe with difficult instructional reading on book ret?
Reddish-pink, bright, with to against (-0.50 to +1.25), more effort and high cognitive demand
What should you observe with complete frustration or non reading on book ret?
Brick red color, dull, large with (+3.00), cognitive level is too difficult
What equipment is needed for Nott?
Ret, near cards, ruler/bar
What is the procedure for Nott?
Pt wears Rx, place near card at 40 cm and perform ret at the plane of the target, the examiner moves the retinoscope closer or farther until neutrality is achieved
What movement is need if Nott ret shows with movement?
Pt demonstrating a lag, move away
What do you record for Nott?
Target distance, distance ret was for neutrality (the difference between the two is the lag/lead)
T/F in Nott lenses are added
False, only the ret distance is changes
What is more difficult to estimate using Nott?
Larger lags/leads
T/F there is a non linear relationship between accommodative stimulus and response
True
As accommodative stimulus increase, accommodative response____
Increases but lags behind more and more each time
What is the stress point?
As a target moves toward a patient she reacts to the stress of the near target with a physiologic response
What equipment is needed for stress point?
Ret, Wolff wand, probe lenses, yardstick
What is the procedure for stress point?
Ret at 20 in/50 cm from patient’s eyes, move the target closer to the patient and look for a change in reflex brightness not motion, repeat with probe lenses
What change should you see in the retinal reflex during stress point testing?
Brightness dulls then returns to prior level of brightness
What is the stress point?
The distance where the reflex changes
What do plus probe lenses do to a stress point?
Shift the stress point closer because patient fixates without stress
What is the expected stress point of a child?
4 inches closer than Harmon distance
What is the expected stress point of an adult?
6 inches from the face
High lag may be related to which types of accommodative dysfunction?
Insufficiency and infacility
A high lag may correspond to what refractive conditions?
Uncorrected hyperope or myope, overminused
A high lag may coincide with what vergence dysfunction?
Esophore with poor ranges
A low lag may correspond to what accommodative dysfunction?
Accommodative spasm
A low lag may correspond to what refractive condition?
Overplussed
A low lag may be due to what vergence dysfunction?
Exophore with poor ranges
What is incorporated in “just look”?
No lenses, compare each eye for color brightness motion and quality, looking at target? Only target and not faces? What happens when target moved to the side? How stable is the reflex?
T/F the just look technique incorporates neutralization
False
