Clinical Optics Flashcards
Orthokeratology using RGP lenses can help reduce what problem?
low amounts of myopia up to -6.00 D and low amounts of astigmatism (1.75D)
Light property used by scanning laser polarimeter to measure nerve fiber layer thickness
polarization
Lensmaker’s equation
P = (n2-n1)/r
N1 and n2 are refractive indices of the regions to the left and right of the refracting interface
u is the distance from the source object point to the refracting interface
v is the signed distance from the refracting interface to the inmage of the source object point and r is the signed radius of curvature fo the refracting interface
Increasing the dioptric power of a convex lens has what effect on focal length
reduction
SAM-FAP rule
steeper CL add minus - Flatter Add Plus
4 year old with 20/25 each eye has hyperopia of +1.75 sphere OU. Treatment at this time?
No treatment. Unless esodeviation, anisometropia or evidence of reduced vision, not necessary to correct low hyperopia.
What does Dk/t describe in a contact lens?
oxygen transmissibility/permeability of the lens - depends on the lens material and the central thickness (L)
DK - oxygen permeability of lens material where D is diffusion coefficient for oxygen movement in the material. K is the solubility constant of oxygen in the material
Wetting angle
refers to the wettability of a lens surface. A low wetting angle means water will spread over the surface, increasing surface wettability. A high Dk/t and low wetting angle are desirable.
Optical advantage of a Galilean telescope is used by surgical loupes?
the image orientation, which is upright
high-powered negative ocular lens (eyepiece) and low-powered positive objective lens separated by the difference between their focal lengths.
Post-operative topography shows irregular astigmatism. Treatment
gas-permeable contact lens or other rigid contact lenses neutralize irregular astigmatism because tear fluid fills irregular space between lens and cornea
Property illustrated by the ability of a light wave from a laser to form stable interference fringes with another wave from the same beam, separated in time.
temporal coherence
physical extent of the light source and presence or absence of a fixed phase relationship between different parts of a light source
spatial coherence
variation of refractive index with frequency and is unrelated to interference
Dispersion
brightness of a source
intensity
Excimer laser removes corneal tissue by what light-tissue interaction and at what wavelength of light?
Photoablation; 193 nm
Rhodopsin absorbs this light best
green - 510 nm
light-tissue interaction and wavelength of Nd:YAG laser
photodisruption 1064 nm
Entrance pupil varies from the actual pupil by what amount?
13-15%
cornea has high plus power, image of the pupil is not the same size as the actual pupil (image seen is ‘entrance pupil’)
How does smaller radius of a base curve affect steepness of lens
smaller the radius of base curve, the steeper the lens
Type of fit if base curve of RGP lens is smaller than base curve of cornea
apical clearance
cornea and RGP have the same base curve
apcial alignment
base curve of a lens is larger than the cornea, producing a flatter RGP in comparison to the cornea
Apical bearing
manifesting a 92 year old with BCVA 20/100. Technique
refine refraction using larger-step changes in shpere and cylinder. +/- 0.75 or 1.00 D in sphere and 0.75 to 1.00 change in jackson cross cylinder
What adjustment should be made to IOL power selection in an eye containing silicone oil?
Increase IOL power by 3-5 D if the silicone oil will remain in the eye.
creates negative lens power if biconvex IOL (standard in US)
Presbyopia-correcting lens is more effective at higher lens power
crystalens IOL
What logMAR value is equivalent to a Snellens VA of 20/20?
0.00
What is logMAR
base-10 logarithm of the minimum angle of resolution
What lens design would lead to a higher rate of capsular opacification?
lens with a round edge
Option for least image magnification in an aphakic patient
posterior chamber IOL (PCIOL)
Aphakic spectacles 20-35% magnification
CL 7-12% magnification
ACIOL - 5%
Retinal image size in the Gullstrand model is based on this primciple
geometric principle of similar triangles
Information needed to prescribe the most accurate add?
Amplitude of accomodation and reading distance
Select a lens that keeps half the amount of accomodation in reserve
One focal line falls on the retina while the other focal line lies posterior to the retina
simple hyperopic astigmatism
One focal line falls on the retina, other focal line lies anterior to the retina
simple myopic astigmatism
Both focal lines lie posterior to the retina
Compound hyperopic astigmatism
Both focal lines lie anterior to the retina
compound myopic astigmatism
energy causes active medium’s electrons to rise to a higher energy state
population inversion
When does stimulated emission occur?
When some high-energy electrons undergo spontaneous emmsion generating photons and if these photons encounter other high energy electrons, stimulated emission occurs
How much does a 15D prism bend light in degrees?
8.53 degrees
for small angles, prism diopters produces a little more than half a degree of deviation
