Entrance test Flashcards
Hirschberg test
- rough objective estimate measurement of deviation/strabismus
- useful in young and cooperative patients
How to do a Hirschberg test
A penlight is held straight in front of a patients face at about 50cm. The patient is instructed to fixate on the penlight with both eyes open
-finds if eye is turned out or in
Do you do Hirschberg one eye at a time or two?
- one eye at a time
- observe the position of corneal reflex
3 possible corneal reflexes in Hirschberg
- center of pupil
- nasal to the pupil
- temporal to the pupil
Nasal to the pupil
positive angle lambda/kappa/ exo posture
temporal to the pupil
negative angle lambda/kappa/ eso posture
strabismus
- if the reflexes are not in the same relative position
- the reflex will not be in the center of the deviated eye and it will be different from the relative angle lambda in that eye
absence of strabismus
the corneal reflex should be centered in both eyes
how to determine the amount of deviation
for 1mm of estimated deviation, it is approximately a deviation of 22 prism diopters
recording Hirschberg
- indicate that you did Hirschberg
- if no strabismus, record Ortho or symmetrical
- strabismus present, record the deviated eye, the size and direction of the deviation
Hirschberg: 44pd LET
Krimsky test
-use prisms to determine the angle of deviation seen on Hirschberg test
-not as accurate, only when you can’t perform cover test
-
How to of Krimsky test
-prisms are placed in front of the fixating eye until the corneal reflexes are symmetrical
what kind of prism for esotropia?
BO
what kind of prism for exotropia?
BI
Near Point of Convergence (NPC)
- determines the ability to converge and maintain fusion
- both eyes on one target, ability to read
How to start NPC
- done with correction, good lighting, and start at about 40cm
- requires transilluminator, red glasses (if they don’t do well), near accomidative target (a 20/30 letter)
How yo do NPC
- tell pt to look at light
- ask if it is single or double, if double, move target further back
- move target towards pt while paying attention to eyes
- move it into the pt until the pt reports double or you see one eye loses fixation
- move target back again until the pt reports single vision
breakpoint
-move the target in until the pt reports double or you see one eye loses fixation, this distance is the break point
recovery
Move the target back again until the patient reports single vision or where you notice refutation, measure this distance, this is the recovery
NPC normal findings
Break 2.5cm/recovery 5cm, or, TTN (to the nose)
NPC abnormal
- repeat with red glass over right eye (or red green glasses)
- repeat 3rd time with an accomidative target
What does red/green glasses do for NPC?
dissociates what both eyes are doing. Eyes will recede more
convergence insufficiency complaints
repeat multiple times, there will be changes in the NPC each time because of fatigue
convergence is closely associated with what?
accommodation
What to record for NPC
- sc/cc
- target used
- distance (cm) where there was a break or diplopia (from bridge of nose or spec plane)
- distance of recovery
- deviated eye and direction
- diplopia or suppression(break without diplopia)
example
-NPC cc light: TTN
-NPC sc light: 10cm/15cm, OD out, suppression
red/green:15cm/20cm, OD out, suppression
accommodative: 12cm/16cm, OD out, suppression
What can a receded NPC cause?
- binocular vision problems
- eyestrain/asthenopia
- reading difficulties
- difficulties with near point tasks
Amplitude of accommodation
- measures patient ability to accommodate (in diopters)
- Pt wears correction, near point accommodation target, occluder, illumination
- MONOCULAR
Push up method
- tell pt to occlude one eye, tell patient to look at a row of letters (one or two lines better than BCVA at N)
- tell pt to keep the letters clea
- slowly move the letters closer to the patient, until the patient reports blur
- measure distance from patient’s spectacle plane in cm and convert to diopters
- occlude other eye and repeat
near point of accommodation
Where it begins blurs when the target is too near to them for them to accommodate
Pull Away method
- Monocular
- tell pt to keep letters clear
- hold target very close to pt open eye
- slowly move letters away from pt, until pt reports clarity
How to record Amp of accommodation
- method used (push up or pull away)
- amplitude of accommodation (D) for each eye
example
Amp of accommodation: 9D OD, 10D OS
How close should the readings be for both eyes for Amp
within 1 diopter
What is expected amp?
- OU within 1 diopter
- accommodation decreases with age, meds, disease
Hofsetter’s formula
minimum expected amplitude = 15-0.25(age)
You can also use Donder’s table, which basically tells you the same numbers
Things that affect accommodation
- age
- meds (CNS stimulants, tranquilizers, antihistamines, cycloplegics, antidepressants)
- iridocyclitis
- trauma
- alcohol
- some glaucomas
- DM, MS
Binocular vision
-allows us to appreciate many aspects of a target
binocular vision and sensory system
constructs single perception from 2 retinal images
-achieves single image from both eyes, gives distance of the target
binocular system and motor system
vergences and eye movements (depth)
- coordinates the orientation of the eyes in all distances, and on your moving targets
- coordinates WITH THE ACCOMMODATIVE system to maintain a clear image
poor binocular vision leads to
- fatigue
- eye strain
- headaches
binocular vision is in jeopardy in
- eye disease
- strabismus
- trauma (TBI)
Little disparity in binocular vision
all these systems work well, they give one image from both retinal images and high resolution
binocular advantage
advantage over monocular vision and monocular clues (depth, more precise, quicker)
what is the best indicator of binocularity?
stereopsis
an indicator of binocularity
the sensory and motor fusion of vision; also shows if accommodative and vergences systems are working well
Fusion
how the eyes unite
3 degrees of fusion
- simultaneous perception and superimposition (1st degree)
- flat fusion (2nd degree)
- Stereopsis (3rd degree)
simultaneous perception and superimposition
- NPC break
- 1st degree
flat fusion
- 2nd degree
- NPC recovery, 2 images into 1 (not perceiving depth)
stereopsis
- 3rd degree
- to get stereopsis, binocularity has to be excellent to fuse fine disparity
purpose of stereopsis
to measure fine depth perception by evaluating the ability to fuse stereoscopic targets
equipment needed for stereopsis testing
- polaroid glasses (or R/G glasses depending on test)
- stereo book
- Pt wears polaroid glasses over near correction
what is testing distance for steropsis
40cm with overhead light, avoid glare
directions for pt for stereopsis
- direct pt to pg 2 with the smallest targets
- ask which circle is floating
- ask pt to indentify target in space
- repeat until pt misses 2 boxes in a row
- record level of stereopsis
If the pt does not appreciate stereo or is unresponsive
use medium size targets and repeat
if pt identifies all medium size targets on stereopsis..
try smaller targets again
if pt is not able to correctly identify any of the small or medium targets…
show the pt the largest targets
How to record stereo
- at near and test used
- indicate if it was done sc or cc
- recorded in seconds of arc
- if none, record no stereo
example
stereo at N cc: 400 seconds of arc, stereo E
What is expected stereo at near?
20-30 seconds of arc
Worth 4 dot
- assess flat fusion
- detect small central scooter at near (when stereopsis is below normal)
- cc, R/G over correction, red lens over OD.
- test can be done at D and at N at 40cm
What to tell pt to do for worth 4 dot
- tell pt to look at the W4D target with the red dot on top and the white on the bottom
- ask how many dots they can see
W4D: 4 dots
normal fusion
W4D: 2 red dots
only the red eye is used, OS is suppression
W4D: 3 green dots
only OS sees, OD suppression
W4D: 5 dots
- diplopia
- ask where the red or green dots are located, this determines the location of the visual axis
crossed diplopia
- 5 dots
- 2 red dots are on the left side
- exo deviation
2 red dots on left in W4D with diplopia
exo deviation
crossed
uncrossed diplopia
eso deviation
5 dots, the 2 red dots to the right
vertical diplopia
it is possible to perceive this. if the red dots are below the green dots, there is a right hyper deviation
scotoma
dead spot so brain can’t have so much disparity. Brains way of making sure the retina doesn’t see double
- not physical, brain just shuts it out
- can still have good stereo and 20/20 VA
testing for scotoma
- make sure there is a normal flat fusion with W4D at N.
- tell pt to look at flashlight and tell you if there is a change to 2 or 3 dots instead of 4
- slowly move the flashlight away from the pt
- stop when and if the pt says there is a change in the number of dots. If there is no change in the number of dots at 10ft, stop!
When testing for scotoma, if you go all the way to 20ft and there is no change…
no suppression
if there was a change in testing for scotoma..
determine and record which eye is suppressed and at what distance
-ask pt to cover dominate eye, ask if the suppress dots reappear
If dots reappear in suppressed eye
- there is a suppression scotoma under binocular conditions
- if they do not reappear, there is a unilateral scotoma
how to record W4D
W4D: fusion at distance, suppression OD at near
W4D: diplopia, so with right hyper @ N
