Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
75 Cards in this Set
- Front
- Back
|
Spec mag compares image sizes (between 2 eyes/within one eye)?
|
One eye (corrected retinal image/uncorrected retinal image)
|
|
|
What is the shape factor equation?
|
1
---------- 1-(t/n)F F=front surface power |
|
|
What is the power factor equations?
|
1
------------ 1-(h)F F=Back vertex power h= distance from lens to entrance pupil (glasses/cornea to iris) |
|
|
What unit do you use for diatance in the spec mag equations?
|
Meters
|
|
|
What is the assumed vertex distance between the cornea and iris?
|
3mm (don't forget to add this to spec vertex distance ie:12+3=15)
|
|
|
What is the Index, abbe, and specific gravity of Crown glass?
|
Index= 1.52
Abbe= 58 SG= 2.54 |
|
|
What is the Index, abbe, and specific gravity of CR-39?
|
Index= 1.49
Abbe= 58 SG= 1.32 |
|
|
What is the Index, abbe, and specific gravity of Poly Carb?
|
Index= 1.58
Abbe= 30 SG= 1.2 |
|
|
What is the Index, abbe, and specific gravity of Trivex?
|
Index= 1.53
Abbe= 45 SG= 1.1 |
|
|
Knapp's Law:
Correct axial errors with (specs/CL)? |
Specs (at a suggested Vertex distance of 16mm)
|
|
|
Keratometry OD) 44.50
OS) 44.25 Refraction OD) -4.00 DS OS) plano DS Axial or Refractive? |
Axial
|
|
|
Relative distance mag equation?
|
Old dist
---------- New dist |
|
|
Relative size mag equations?
|
New Size
------------ Old size |
|
|
Angular mag is essentially a combination of what two types of mag?
|
Distance and size
|
|
|
Gallilean telescope has what kind of lenses, is (shorter/longer) than keplarian, and has an (inverted/upright) image?
|
+,-
shorter upright |
|
|
Equation for telescope mag?
|
- eyepeice
------------- objective |
|
|
For an uncorrected myope, you would (shorten/lengthen) the tube length of the telescope.
|
Shorten
|
|
|
You have a gallilean telescope with +2, -10. You view an object 40 cm in front of the objective lens. how much do you have to accomodate to see the object clearly?
|
10.41
|
|
|
You have a keplerian telescope. +5, +10. You add a +3.00 reading cap. What is the total mag?
|
-6.00x
|
|
|
What is the standard viewing distance used to compute the power of near magnification devices? (the object is at the primary focal point)
|
25cm
|
|
|
Magnification factor equation for near mag devices?
|
Mag= EquavalentPower/4
|
|
|
What is the equavalent power of a hand magnifyer that is stamped 4x?
|
16D
|
|
|
What is the equation for equvalent power?
|
F=F1 + F2 - d(F1*F2) d=distance between lenses. When regarding near mag devices, F1 is magnifyer power(D) and F2 is amount of accomodation required, add used, or end cap used.
|
|
|
Equation for Lateral Mag?
|
Old vergence
--------------- New vergence |
|
|
You have an object 4.5cm in front of a +15 lens. What is the Lateral mag?
|
+3.00x
|
|
|
You have and object at 30cm and move that object to 39.35cm. What is the relative distance mag?
|
+0.76x
|
|
|
What is the equation for angular mag (aka: total mag)?
|
Size mag (or lateral mag) * Distance mag
|
|
|
A patient holds his reading material at 30cm. He then places a stand magnifier (Fe=+15.00D, object distance of 4.5cm from lens) on his reading material. If he keeps the reading material at 30 cm, how much magnification does he get?
|
+2.29x
|
|
|
If patient reads 20/40 letters at 20 feet through best correction and needs to read 20/20 letters at the same distance, what is the required mag?
|
+2.00x
|
|
|
When viewing a patient's eye through a keratometer, the mires look squished horizontally (looks like hamburger). At what axis (90/180) is the patient's astigmatism?
|
@ axis 90. The more powerful the mirror (eye) the more minification is perceived.
|
|
|
Describe spherical aberration
|
Object is on/off axis, power of a lens gets more powerful the furthur away from center.
|
|
|
Aberrations: Describe oblique astigmatism
|
Off axis object results in non-perpendicular rays hitting lens which affects the amount of refraction.
|
|
|
Aberrations: Describe coma
|
Off axis object, magnification is varied as height above the axis is varied
|
|
|
Pantoscopic tilt of a (+) lens induces what type of astigmatism?
|
Plus cyl axis 180 (minus cyc axis 90)
|
|
|
Which branch of the tscherning eclipse do we use (Walliston/Oswalt) and why?
|
Oswalt, thinner lens design
|
|
|
Aberrations: Which type of lens (+/-) results in barrell distortion?
|
(-)
|
|
|
In the USA, the index of refraction (n) is computed using what wavelength of light?
|
Yellow heluim 587.6
|
|
|
velocity of light?
|
3.0+10^8
|
|
|
Equation describing change of velocity of light as related to index of refraction?
|
n= speed of light / speed of light in material
|
|
|
What wavelength of light is affect more by refraction (long/short)?
|
Short
|
|
|
What wavelength of light is affected more by defraction (bending around edges or pinhole) (long/short)?
|
Long
|
|
|
Aberrations: Dispersion refers to the (interval of sterm) of the different wavelengths of light caused by the refractive differences. What is the equation?
|
w= n - n / n -1 difference of n of blue & red over n of yellow light
|
|
|
what is the equation for abbe number?
|
Abbe = 1/w w=abberation
|
|
|
Equation for sag?
|
s= h^2 / 2r
r=radius of curvature h=half the chord (half diameter of lens) |
|
|
Calculate the sagitta of a crown glass surface having a refracting power of 15.00D and being 42 mm in lens diameter.
|
6.3mm
|
|
|
Lens clocks are calibrated for what index and what is the equation the convert?
|
1.53, reading * (true index-1 / clock index-1)
|
|
|
A 10 diopter base down prism will deviate light (x cm) (down,/up) on a screen at what standard distance?
|
10cm down on a screen 100cm away. (image of light moves up from screen's perspective)
|
|
|
Patient has Rx of -2.00 sph OD and -5.00 sphere OS. If he reads 10mm below the OC, how much prism is induced and how can we correct it with a slab-off bifocal?
|
3BD OS, slab-off in OS
|
|
|
What is the equation to calculate the amount of light reflected form a surface?
|
Light reflected = [(n-n)^2 / (n+n)^2] *incident light
|
|
|
How much light is transmitted
through a CR-39 lens, assuming no absorption and perpendicular incident light? |
~92% don't forget to calculate reflectance at each surface interface
|
|
|
Equation for the ideal index of a single-layer AR coating?
|
ideal coating index = square root of lens index
|
|
|
Equation of ideal thickness of AR coating?
|
t= wavelength/4*coating index
|
|
|
The tindell scattering effect of light refers to light being scattered by a homogenous suspension or colliod structure. This gives the color to what anatomical structure?
|
Iris. It's what potentially makes the iris blue.
|
|
|
Minimum blank size?
|
Minimm blank size=ED+2(d)+2mm
d=decentration |
|
|
If you combined two prisms (2BU,1BO) over the OS, what would be the resultant prismatic effect and its estimated axis?
|
2.23@63
|
|
|
Where is the optical center of a flat top seg (in relation to upper edge)?
|
5mm below upper edge
|
|
|
Where is the optical center of a exectutive seg (in relation to upper edge)?
|
0mm (the optical center is at the edge)
|
|
|
Where is the optical center of a round seg (in relation to upper edge)?
|
at the center (radius)
|
|
|
In a trifocal, the intermediate add is usually what?
|
1/2 near add
|
|
|
Vocabulary: Inset refers to the difference between what two points?
|
Geometrical center of frame eyepiece and the MRP (main reference point). This is adjusted to match the optical center of the lenses to the patients PD
|
|
|
Vocabulary:Seg inset refers to the difference between what two points?
|
MRP (distance optical center) to seg optical center. Accounts for near PD
|
|
|
Vocabulary: Total inset refers to the difference between what two points?
|
Geometrical center to seg optical center.
|
|
|
A frame measures 54x18. The patients distance PD=66, near PD=62. What is the inset, seg inset, and total inset?
|
3mm,2mm,5mm
|
|
|
The correct way to measure add power in a lensometer is with the temples towards you. Are you measuring front of back vertex power?
|
Front
|
|
|
Find the image jump in bifocals, given an rx of +2.00-1.25x180, add= 2.00. Flat top 28. Distance from optical center to top of seg is 4mm.
|
1.00BD (you don't need any info except add power and type)
|
|
|
Find the vertical imbalance that results when looking 10mm down:
OD:+1.50-1.00x90 OS:+0.50-0.75x180 Add:1.50, flat top, drop: 4mm PD:64/58 |
OD: 1.5BU, OS:0.25BD = 1.75BUOD
(pg 83) |
|
|
Relative spectacle mag compares the mag experience by a corrected eye to that of a "standard eye". What power is the standard eye?
|
+60D
|
|
|
For axial ametropia, which results in the largest retinal image size? (hyperope, emmetrope,myope)
|
Axial myope.
|
|
|
The 4 types of aniseikonia are Anatomical, induced, overall, and meridonal. Define each.
|
Anatomical: Discrepancy in density of photoreceptors
Induced: (spec mag differences) Overall: Sphericall symmetric difference Meridional: High astigmatism |
|
|
For large differences in relative spec mag, you want to prescribe a thin, flat lens for the eye with (high/lower) RSM?
|
Higher
|
|
|
What amount of ametropia is considered the division between specticle and axial? (2D,4D,6D,8D,10D)
|
4D
|
|
|
The general rules states that every 1D of difference results in what percentage of size difference?
|
1%
|
|
|
Which lens would you make thincker to decrease RSM? OD -2.00, OS+1.00
|
Increase thickness of OD (-2.00)
|
|
|
If a patient is OD +2.00, OS +4.00, which eye will he use for near? Which for distance?
|
OD for both
|
|
|
If a magnifyer is labeled as a collimating lens, what does that mean?
|
The object is placed at F
|
