Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
32 Cards in this Set
- Front
- Back
|
Torsional and horizontal controls rotate around ______________________? What does this allow for?
|
Centre of rotation of the Eye (Axis of Fick)
Allows for measurements in all positions of gaze |
|
|
What is the power supply of the synoptophore?
|
6 V
|
|
|
What is the optical power of the eyepiece?
|
+ 6.50 Diopters
|
|
|
What is a disadvantage about the synoptophore which relates to the plus powered eyepieces?
|
focal length of +6.50 = 0.154 m
synoptophore is a distance instrument, esos are overestimated |
|
|
How can you alter the synoptophore to turn it into a near instrument? What does this introduce into your results?
|
Place -3.00 lenses over the eyepieces. This induces accommodation. This however adds convergence since it is now a near instrument.
|
|
|
How many diopters of convergence are executed per diopter of accommodation?
|
3 diopters convergence/diopter accomm
|
|
|
When using the synoptophore as a near instrument, how do you correct for the induced convergence?
|
add 18 diopters to XT measurements, subtract 18 dopters from ET measurements
|
|
|
Define Simultaneous Perception
|
Ability to perceive and superimpose two dissimilar images - one from each retina
|
|
|
What size image subtends 1 degree on the retina?
|
Foveal
|
|
|
How many degrees does a macular size image subtend?
|
less than 3 degrees
|
|
|
What size image subtends less than 5 degrees on the retina?
|
Para-Macular
|
|
|
How many degrees does a peripheral image subtend?
|
more than 5 degrees
|
|
|
How are simultaneous perception slides designed?
|
two slides with completely different images are put in at the same time for example a cage and a parrot. Patient could see the parrot in the cage - they have sim perception - or alternate between the parrot and the cage.
|
|
|
What is fusion? How are the fusion slides designed?
|
Ability to join two similar images into one composite image.
Slides - same pictures with two slightly different controls - for example a guy with a red hat in one and the same guy with a briefcase in the other. fusion gives a guy with a red hat and a briefcase |
|
|
What is stereopsis? How are the slides designed?
|
Binocular depth perception
Slides - identical pictures but one with a slight horizontal displacement should yield a 3D image |
|
|
After centering the patient's pupils with the centre of the eyepiece, what do you center next?
|
corneal light reflexes - one at a time extinguish light before one eye and center them with white line on the tube
*** examiner must close their eye at the same time |
|
|
Explain how the objective angle is measured
|
- use a slide with appropriate target size for the patient's vision
- set scales to 0 - MAKE SURE THEY CAN SEE EACH IMAGE ALTERNATELY - fixing eye views the solid target - adjust the tubes until you neutralize the deviation |
|
|
How do you measure the subjective angle?
|
After measuring the obj angle - ask patient if they see both images at once - are they superimposed? if so, subjective angle = objective angle.
if not - allow patient to move the image horizontally until they are superimposed then this is the sub angle |
|
|
What is the major cause of no subjective response with the simultaneous perception slides?
|
suppression
|
|
|
How many diopters is one degree?
|
2 diopters
|
|
|
What important questions do you ask a patient when assessing fusion?
|
- do you see one image or two?
- make sure they see BOTH controls if they report seeing one image - red hat and briefcase? if not = suppression - if sees two images - ask patient to superimpose them manually to try to fuse |
|
|
How would you record fusion range?
|
IF patient can join the two images, lock the tubes. Now DIVERGE them until patient sees two images or one control is lost. Then do the same but CONVERGE them. Record the range
Divergence: - Convergence:+ |
|
|
To measure stereo, first you must insert the stereo slides at a certain angle. What is this angle?
|
Angle determined by the fusion slides
|
|
|
Important questions to ask about stereo?
|
- Ask patient if they see any depth in the pictures first
- ex. swing - forward or away? - ex. fish - order of fish? |
|
|
In ARC, the subjective angle is _________ than the objective angle.
|
smaller
|
|
|
Synoptophore is mostly used today to assess?
|
binocular potential
|
|
|
Advantages of synoptophore?
|
1. measurements can be made horizontal, vertical or torsional
2. measurements can be made in all positions of gaze 3. objective and subjective 4. trial lenses can be mounted in lens holder 5. size appropriate slides available 6. tests all 3 grades of BSV 7. IPD adjustable 8. distance can be turned into near instrument 9. can do many tests in small amount of time 10. interesting fixation targets 11. examiner can watch patient throughout testing |
|
|
Disadvantages of synoptophore
|
1. heavy and cumbersome
2. although distance instrument, patients tend to converge due to awareness of near 3. relies heavily on subjective response 4. angle may vary according to accommodation 5. not suitable for very young children 6. expensive 7. cannot be used with low vision patients |
|
|
What are Braddick slides?
|
random dot stereograms used to measure specific amount of stereo
|
|
|
What is aniseikonia? What are aniseikonia slides?
|
difference in relative size of images between eyes
patient matches control figure with those in other eye of increasing size |
|
|
What are Haidinger's brushes?
|
faint blue and yellow dumbbell shaped images produced in the human eye by selective absorption of polarized light by yellow macular pigment
treats eccentric fixation |
|
|
How can eccentric fixation be detected with Haidinger's brushes?
|
in central fixation, centre of brushes is superimposed at fixation point. in eccentric fixation, brushes appear peripheral or are not seen.
|
