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Optical Theory I > Visual Acuity > Flashcards

Visual Acuity Flashcards

1
Q

visual acuity

A

the criterion for an adequate refraction
foundation on which the vision exam is built
not necessarily the final endpoint of an exam

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2
Q

Types of visual acuity

A

Detection acuity
Resolution acuity
Recognition acuity
Contrast sensitivity

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3
Q

Detection acuity

A

seeing an object on a background that is different from the object itself

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4
Q

Resolution acuity

A

the ability to see a misalignment (a line is broken)

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5
Q

Recognition acuity

A

being able to identify two or more objects on a contrasting background
acuity that is most commonly thought of

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6
Q

Low literacy or non verbal tests

A

Tumbling E & Landolt C

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7
Q

Recognition acuity tests

A

Snellen is the most common (E on top)

Logmar chart

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8
Q

Contrast sensitivity

A

minimum contrast that is still perceivable by the patient
measured by test gratings of equal width
can vary contrast and frequency
30 cycles/degree = 20/20

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9
Q

Visual Acuity Notation Numerator

A

how far away the patient stands from the object

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10
Q

Visual Acuity Notation Denominator

A

distance at which the letters subtend 5’ of arc at the nodal point of the eye or the letter the patient reads

normal terms: distance at which the letters take up five minutes (5/60ths) of one degree of space of their visual field

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11
Q

What 20/20 means

A

If a person is standing 20 feet away from a target, the smallest letters identified would subtend 5’ of the visual field

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12
Q

What 20/40 means

A

A person standing 20 feet away from a target, the smallest letters identified would subtend 5’ of arc if that person stood 40 ft away

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13
Q

Smallest object a human eye can see

A

1’ of arc detail

limited by cone density and neural connections

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14
Q

Finding 3 month old visual acuity

A

fix & follow in both eyes

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15
Q

Finding newborn old visual acuity

A

pupils react to light

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16
Q

Finding 93 year old visual acuity (cateracts)

A

finger counting from 1 ft away

if it’s really bad may need to ask for which direction your hand moves

17
Q

Objective acuity measurements

A

optokinetic (OKN) drum

catford drum

18
Q

OKN drum

A

measures visual perception based on the optokinetic response (subconscious response to movement)

19
Q

Catford drum

A

tests for visual perception also using optokinetic response, but has bars of varying sizes
no longer used (scary metal thing)

20
Q

VA sc

A

visual acuity without correction

21
Q

VA cc

A

visual acuity with correction

22
Q

Snellen letter size

A
  • indicates at what distance a letter subtends 5’ of arc at the nodal point
  • based on the tangent of the angle
  • height of a 20/20 letter for a chart designed for 20 ft (6 m) is 8.73 mm (tan(5’) = height * 6000 mm)
23
Q

Relationship between Snellen Letters

A

Linear

a 20 ft chart: 20/200 = 87.3 mm, 20/40 = 17.46 mm, etc

24
Q

Hardest Snellen letter

A

B

25
Q

Easiest Snellen letter

A

L

26
Q

Myopia

A
  • aka near sighted
  • can’t see well far away
  • can see nearby
  • have elongated eye : light focuses in front of eye : need - lens to correct
27
Q

hyperopia

A
  • aka far sighted
  • can’t see well nearby
  • can see far away
  • have shortened eye : light focuses behind eye : need + lens to correct
28
Q

Things that affect visual acuity

A

pupil size

pinhole acuity

29
Q

Pinhole acuity

A

has a pinhole of 1 mm diameter

tested with a pinhole occluder

30
Q

Alger brush

A

Used to help mend rough edged corneal abrasions (cleans up lines and helps epithelial cells quickly & cleanly heal)
*Bowman’s stops it

31
Q

Layers of the cornea

A 
Carneal epithelium
Bowman’s membrane
Stroma
Dua’s layer
Descemet’s membrane
Corneal endothelium
32
Q

Dilation drops

A

Excitate dilater & paralyze sphincter

Optical Theory I (1 decks)

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