9 - LV/Magnification Flashcards Preview

KMK - Physiological Optics > 9 - LV/Magnification > Flashcards

Flashcards in 9 - LV/Magnification Deck (23)
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1
Q

Describe angular magnification

A

Result of an incr in retinal image size of an object by introducing an optical system (i.e. LENSES USED) in bw the object and the eye

  • hand-held/collimating
  • stand/non-collimating
2
Q

Difference bw lateral and angular magnification

A

L: compares object size to image size

A: compares original retinal image size to retinal image size when viewed thru an optical system

3
Q

Hand-held magnifiers

-describe

A

High plus-powered lens

Puts object of interest at the primary focal point of the magnifier

  • this creates an image at infinity by collimating outgoing light
  • no need for accommodation when using
4
Q

Hand-held magnifiers

-an object at the primary focal point

A

Once there, the HHM-object system can be moved anywhere in front of the eye and total magnification will remain the same
-as lens-eye distance changes, the spectacle mag of the lens changes, however there’s an equal but opposite change in RDM = 0

5
Q

Hand-held magnifiers

-what changes/doesn’t change when HHM is moved closer/farther from eye

A

Changes: linear FOV (incr when brought closer to eye)

Does not change: angular/total mag, accommodation (not needed still)

6
Q

Stand magnifiers

-describe

A

High plus-powered lens mounted such that object to lens disparity is FIXED

  • for most SMs, the object is located INSIDE the primary focal point
  • upright, magnified, virtual image
  • need for accommodation (light is still diverging as it leaves)
7
Q

Telescopes

-describe

A

For magnifying distance objects

Both light in and out is parallel/plane = no need for accommodation

8
Q

Telescopes

-entrance and exit pupils

A

EnP = objective lens

ExP = image of objective lens thru ocular lens

9
Q

Telescopes

-meaning of label A x B

A
A = magnification
B = diameter entrance pupil (dent) in mm

E.g. 4 x 45 = 4x mag, 45mm dent

10
Q

Telescopes

-field of view dependent on (2)

A

Diameter of EnP - incr dent will incr exit pupil = incr FOV

Diameter of ExP - will continue to incr FOV by incr dex until dex becomes larger than the pt’s pupil, at which point the pupil is the limiting factor

11
Q

Telescopes

-Keplarian

A

Both plus lenses

Inverted, real, magnified image
-need another lens to upright -> longer tube, heavier

AS and EnP are the objective
ExP is behind ocular (outside/in free space) = LARGER FOV bc can align with pupil
-typically very small = DIM image

12
Q

Telescopes

-Galilean

A

Positive objective, negative ocular lens

Upright, magnified image
-objective lens forms real image that becomes a virtual object for ocular lens

AS and EnP are the objective
ExP is inside telescope = SMALLER FOV
-typically larger = BRIGHT image

Limited to 4x mag

13
Q

Telemicroscopes

-describe

A

Telescope + reading cap

Used for viewing near object
-reading cap acts as a HHM - object located at primary focal point -> plane waves enter TS

14
Q

Spectacle-mounted telescopes

  • center fit
  • bioptic fit
A

C: in LOS = continuous viewing, requires minimal training, shouldn’t walk with

B: in upper portion of spectacle lens, used for spotting, significant training required
-uses include classroom work, driving, traveling, grocery stores

15
Q

Reverse telescopes

  • use
  • describe
  • alternative
A

Expand FOV - pts with RP, advanced glaucoma, etc.

Pt looks thru objective lens = minifies objects

  • must have good central acuity
  • most often hand-held, 2.5-4x Galilean

Minus lenses - esp successful with -5 to -10D

16
Q

VFD

  • most effective method
  • prism orientation
A

Scanning techniques

Base toward defect

17
Q

Classifying vision

  • normal
  • near-normal
  • moderate LV
  • severe LV
  • profound LV
  • near-blind
A
Snellen:
12 to 25
30 to 60
70 to 160
200 to 400
500 to 1000
Worse than 1000
18
Q

M notation

A

1M

  • subtends 5 arcmin at 1m
  • equals 20/20
  • linearly = 1.45mm (or 1/16th of an inch)
19
Q

Just noticeable difference

A

Smallest lens power change the pt can detect

JND = snellen ÷ 100

E.g. 20/400 pt’s JND is 4D
-when doing trial frame use +/- 2.00 D flippers

20
Q

For a pt that uses eccentric viewing, the point located adjacent to the scotoma that is used for viewing is called

A

Preferred retinal locus (PRL)

21
Q

Examples of contrast sensivity charts (3)

A

Pelli-Robson: large letters, uniform size

Vistech system: sine-wave gratings

Bailey-Lovie: 3 charts, each at diff level contrast

22
Q

Filters

  • neutral density filters
  • blue blockers/amber tints
A

NDF: reduce glare, good for pts with photophobia, all wavelengths are transmitted equally so no effect on contrast

BB/AT: reduce transmission of short-wavelengths -> reduced glare and enhanced contrast

23
Q

VF testing

-central scotomas are detected most effectively with

A

Scanning laser ophthalmoscope