double vision Flashcards
three main causes of double vision
pathology
BV problems
ophthalmic (add type or PDs)
what amount and direction of prism would be induced in these glasses: OD:-2.50 DS OS: -2.00 Add: +2.00, FT 28 Pt PDs: 28/28(distance) and 26/26 (near)
0.9PD BI
2mm difference per eye
OD: 0.2x 2.50=0.50PD
OS: 0.2 x 2.00=0.40PD
0.50+0.40=0.90PD BI
what type of mergence movement will be induced by BI prism? what mergence ranges must be large enough to compensate in order to prevent symptoms?
divergence
NFV
what is the image jump when the patient looks into her bifocal OD:-2.50 DS OS: -2.00 Add: +2.00, FT 28 Pt PDs: 28/28(distance) and 26/26 (near)
1PD BD OU
(.5)(2.00)=1BD
a pair of glasses measures 3BO and 2BU OD and 3 BO and 3 BU OS. what is the total prism?
6BO
1BU
to verify the ocular misalignment that would require 6BO and 1BU in glasses, how would the vertical and horizontal lines on Maddox rod appear?
right; below
what is the power and orientation needed for fresnel prism to be added to the glasses with 6 BO and 1BU
6.08PD at 9.46 degrees
use pythagorean theorem and draw out a vector. solve for C^2 to get the prism. we know the prism must be between 0-90 so pick the one that falls in that range
anytime a question asks to calculate something about a patient looking away from optical center, what is it asking you to do
use prentices rule
4 ways to use prentices rule
decentration
image jump
vertical imbalance
total prismatic effect
think in cm and draw out prism direction
combining prism between eyes
bases opposite=add
bases same=subtract
combing prisms in same eye
vector addition
- draw arrow head towards base
- use pythagorean theorem
prentices rule
PD=dP
d=distance from the optical center in cm
P=power of the lens
BI prism causes images to appear
further away
BI prism causes divergence or convergence?
divergence
what type of vergences are needed to look through BI prism
NFV
PFVs
tested directly with BO prism or indirectly with plus lenses. Plus lenses relax accommodation which relaxes convergence. patients must use PFV to counteract this divergence to maintain fusion
BOP
exophorias require large ____ranges
PFV
NFV
tested directly with BI prism or indirectly with minus lenses. Minus lenses stimulate accommodation, which stimulates convergence. Patients must use NFV to counteract this convergence to maintain fusion,
esophorias require large ____ranges
NFV
what tests mergence stamina
facilities
which should you test first, PFV or NFV
NFV (BI)
convergence could interfere with the results of the test
imAGE jump
the amount of prism induced at the bifocal line due to the ADD power when the patient looks into the bifocal segment. calculated using only the add power and the distance between the top of the segment and the optical center of the segment (the style of the bifocal).
what is the distance between the optical center and the edge of a FT 28
5mm
what is needed for imAGE jump
add power and the type (the type tells us how far the bifocal is from the optical center
what is the distance between the optical center and the edge of a ribbon bifocal
7mm
what is the distance between the optical center and the edge of a round 22
radius (11mm)
what is the distance between the optical center and the edge of a executive
0
what can you do to reduce image jump
PAL or executive
combining horizontal prism
- if the prism over the left and right eyes are in the same direction (both BI or both BO), ADD the prisms
- if the prisms over the left and right eyes are in oppose direction (BI in one, BO in the other), subtract the prisms
combining vertical prism
- if prisms over the left and right eyes are in the same direction (both BU or both ND), SUBTRACT the prisms to determine the total prism power
- if prisms over the left and right eyes are in the opposite directions (one BU and one BD), ADD the prisms to determine the total prism power
Maddox rod
a dissociated, subjective rest that determiners the magnitude and direction of a deviation (cannot tell phoria from tropia). it contains a series of stacked cylinders that forms a line image on the retina when a patient views a light source
measuring horiztonal deviation with Maddox rod
the Maddox rod striations are oriented horizontally to produce a vertical line image for the eye viewing through the Maddox rod while the fellow eye views a point light source
measuring vertical deviation with Maddox rod
Maddox rod striations are oriented vertically to produce a horizontal line image for the eye viewing through the Maddox rod while the fellow eye views a point light source
uncrossed diplopia on Maddox rod
line to the right
Maddox rod and right hyper
red horizontal line below the point light source
