opthl optics Flashcards
how are polarized lenses constructed. what is blocked out
vertically oriented filter to allow parallel light in and block horizontal light rays
liquid crystal displays used for cell phones, tv, laptops. when a polarizing filter is placed in front of the LCD and rotated, what happens
able to tell if sunglasses are polarized
– display on the screen when viewed through lens will darken or blacken out.
- alternative : place 2 polarizing sunglasses perpendicular to each other will result in blockage of light
-
to calculate inset for BF
distance PD - near PD /2
where is segment height measured for PALs
at center of pupil to bottom of deepest portion of lens
for bifocal segment height, where is the the lens dotted on a pair of glasses to be fit?
lens dotted at pt lower eyelid. add 0.5mm for grooved frame (optional)
trifocal measurement vs bifocal measurement
lens dotted at lower pupil margin
which lens allows light to pass through the lens rather than being reflected off the surface of the lens
anti-reflective
– helps w/ glare & digital eye strain
what tint will help to offset effects of overhead fluorescent lighting
light rose or pink tint
- note FL-41 good for migraine HA
for a pt that is 10XP at near, what is observed if maddox rod placed over right eye
what is the set up
red vertical streak to left of the spot of light
SET. UP: placed over an eye with axis horizontal. put modified thorington card 40cm. place penlight through hole
– pt should see letters and number
– if exo deviation, sees vertical streak to left of spot of light (IF over OD)
pt’s subjective is -0.25-1.25x062
if performing astigmatic clock dial, which lines would be boldest?
– multiply smallest number of clearest clock position by 30 degr.
– in this case work backwards.
– axis of astigmatism: 62 deg
– 62/30=2.0666 or 2
– 2-8 line is boldest
javal’s rule
what to do for against the rule
1.25xdifference in keratometry +/-0.50
+0.50
think of it as taxing
spherical aberration
parallel light rays incident on the cornea & lens are bent to a greater degree than axial rays, resulting in image that comes to a point focus in front of retinal plane
corneal arcus is white/yellowish circular band of cholesterol deposits in which layer of the cornea
stroma
Pt presenting with unilateral arcus would need what test done?
doppler ultrasound of opposite carotid artery for potential occlusion
occlusion would interfere w/ blood flow preventing that eye from developing arcus.
difference in pt symptoms for brao vs brvo
brvo – unilater painless LOV
brao– HA, amarousis fugax, unil painless abrupt LOV & abrupt loss of portion of VF
why is ST area of the retina likely to have brvo
ST area of retina has greatest amounts of arteriovenous crossing
during the initial venous phase of fluorescein angiography, what is seen?
late phase?
venous phase: affected area has delayed venous filling & hypOfluorescence superiorly due to blockage by CWS and hemorrhages
late phase: hyperfluorescence over affected vessel and surrounding are due to vascular leakage
ocular manifestations of sarcoidosis
-large mutton fat like keratic precipitates
-dry eyes
– enlarged lacrimal glands
–sheathing of periph. retinal vasculature
–mac edema
Pt suspected of having MS need what exam? what are we looking for?
MRI to confirm plaques of demyelination
people living in which area of the world have a greater chance of developing MS?
norther hemisphere
