Clinical: Von Graefe Phorias Flashcards
Phorometry is testing to assess…
Ocular alignement
Phorometry consists of various ways to…
Measure ocular alignment at different distances
Phorometry consists of various ways to…
Measure ocular alignment at different distances
Different tests used to test phorias:
-cover test
-hirschberg/krimsky
-Maddox rod
-modified thorington
-von graefe phorias
What is binocular vision?
The way the two eyes work together to integrate the images seen by each eye into one image
How does binocular vision work?
Each eye receives an image fo the object being viewed and the info is then sent to the brain where the images are then compared and processed into one image
To achieve binocular vision, retinal images must be:
-In good focus
-similar in size
-similar in shape
-aligned on the fovea of both eyes
Good binocular vision allows for us to have…
Single vision and good depth perception
An object will stimulate different parts of the retina if placed…
In different areas of the visual field
An object in the patients left visual field will stimulate:
-The nasal retina of the left eye
-the temporal retina of the right eye
**and vice versa
The right visual field projects to the…
Left visual cortex
The left visual field projects to the…
Right visual cortex
A visual target on one side of the visual field stimulates…
Certain points on the retina with respect to the fovea
The corresponding points help us…
Detect object location and direction
Heterotropia:
-A manifest deviation of the eye
-visual axes of both eyes do not intersect at a fixation point
-can result in diplopia or suppression of deviated eye
Heterophoria :
-tendency for the eyes to deviate away from bifocal fixation when fusion is broken
Esophoria
Posture of the eyes is inward
Exophoria
The posture of the eyes is outward
Hyperphoria
The posture of the eyes is upward
Hypophoria
The posture of the eye is downward (we never call anything a hypo, we refer to the opposite eye as a hyper instead)
Phorias can be related to:
-abnormalities of binocular vision
Patients need enough convergence and divergence ability to compensate for their phoria especially if they have…
Symptoms of diplopia, eye strain, headaches, etc
Patients should be able to maintain _____, ________ binocular vision
Clear, comfortable
In order for clear and comfortable binocular vision to occur:
-retinal images must be aligned and on the fovea of each eye
-must be able to align their eyes and maintain alignment
Accommodative and alignment/vergence testing can aid in evaluating how…
A patients visual system is functioning day to day
Function of unilateral cover test
To distinguish between Phoria vs tropia
Function of alternating cover test
To determine direction and magnitude of the phoria
Von graefe phorias measures…
The presence, magnitude and direction of a phoria
Von graefe phorias are performed in the _____________
Phoropter
Von graefe is a ____________ measurement
Subjective
Von graefe phorias is performed after ___________ and uses prism to ___________ and ____________
Refraction, break fusion and measure deviation
Image bends towards the _____ in a prism
Apex
During Von graefe phorias, we use different prism over __________
BOTH eyes
Prism over one eye is used to _________________ and the other is used to _______________
Measure the phoria, dissociate the eyes
Distance lateral Von graefe phoria purpose:
To determine the relative horizontal position of the visual axes of the eyes at distance when fusion is broken
Distance lateral Von graefe phoria measures…
Horizontal heterophoria
Target for distance lateral Von graefe phoria:
Single letter two lines larger than the best corrected acuity in the worst seeing eye
What prims are used over each eye in distance lateral Von graefe phoria?
-12prism diopter BI OD (measure the prism = move)
-6 prism diopter BU OS (dissociating prism = remain stationary)
How to direct patient when performing distance lateral Von graefe phoria?
-“you should see two letters, one up and to the right, and one down and to the left”
-“look at the bottom letter and keep it clear”
-“I will move the top letter from side to side. Let me know when it lines up directly above the bottom letter like buttons on a shirt”
To move the letters in a distance lateral Von graefe phoria test …
Gradually reduce the measuring prism (horizontal prism) until pt says they are aligned, go past that point and then go back towards the beginning point (12 pd BI) then average the two measurements if within 3pd of each other
What do you need to change when going from distance lateral phoria to near lateral phoria?
-put in tentative add if presbyopic
-near wings in
-near card at 40 cm
-target is vertical line of isolated letters or single letter
-bright illumination w/ stand lamp
If the patient only sees one target:
-pt could be suppressing (then can’t do test)
-pt is fusion images together (increase the prism further or switch to BO)
If average of the two measurements is zero then….
The patient is ortho
Distance vertical Von graefe phoria purpose
Determine the vertical position of the visual axes of the eyes at distance when fusion is broken
For vertical prisms, what goes over which eye?
OD: 12 pd BI = dissociating prism
OS: 6 pd BU = measuring prism
Use the same directions as the lateral phoria, but this time have pt focus on…
The top letter, tell pt to let you know when the letters line up side by side like headlights on a car
Near vertical phoria test target:
Horizontal line of letters or isolated single letter
Typical phoria test order:
-distance lateral phoria
-distance vertical phoria
-near lateral phorias
-near vertical phorias
Expected phoria values for distance:
-1prism diopter XP (+/- 2pd)
- 1EP to 3XP
Expected phoria values at near:
-3 prism diopters (+/-3pd)
-ortho to 6XP
Important things to remember in Von graefe tests:
-instruct pt where to look during the test
-always instruct pt to keep target clear to control accommodation
-add more dissociating prism if target become clear during test
