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OPT 514 > Visual Acuity > Flashcards

Visual Acuity Flashcards

1
Q

Minimum detectable resolution

A

the threshold size of of a spot required to detect its presence against a background

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2
Q

Minimum separable resolution

A

the least separation between two adjacent points that allows the two to be seen separate.

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3
Q

Recognition test

A

determine the smallest symbols, letters, or words that can be identified correctly

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4
Q

Visual Acuity

A

expresses the angular size of the smallest target that can be resolved by the patient

  • most useful SINGLE test for determining function of the visual system
  • spatial resolving power of the visual system
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5
Q

Snellen Fraction

A

angular size of optotypes by specifying the test distance and the height of the letters.
VA=(test distance)/(distance at which letters subtend 5 minarc)

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6
Q

Decimal Notation

A
  • reduces snellen fraction to decimalized quantity
  • 20/20 is 1.0
  • DOES NOT INDICATE TEST DISTANCE
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7
Q

What are the steps to take when a patient cannot see 20/400?

A

CF,HM, Light Projection, Light Perception

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8
Q

Unaided VA

A

should be tested before corrected VA

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9
Q

Habitual VA

A

VA measured when patient is wearing whatever kind of correction they came in with

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10
Q

Corrected VA

A

VA with best possible refractive correction

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11
Q

Pinhole accuity

A

Increased depth focus reduces blur due to optical irregularities or refractive error.

  • Determines whether reduced VA is due to optical irregularities of uncorrected refractive error.
  • can dullen the light so patients with retinal problems can have reduced visual acuity
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12
Q

Distance for near vision accuity

A

usually 40 cm

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13
Q

Reasons for measuring visual accuity

A
  • refractive and prescribing decisions
  • monitor ocular health
  • application to vision standards(occupation)
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14
Q

Contrast Sensitivity

A

-VA is poorer when contrast is lower

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15
Q

Disability Glare

A
  • Light scatters to reduce contrast, which reduces VA

- used to quantify extent to which certain conditions impair vision in this manner

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16
Q

Potential Acuity

A

can determine visual capability of retina/brain in those with cataracts.

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17
Q

inherited color vision defect

A
  1. inherited: inherited genetic defect. congenital and remains constant their whole life(both eyes are the same)
    - usually red-green
    - cannot be cred, but can be managed
    - non pathological
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18
Q

Acquired color vision defect

A
  • caused by accompanying disease/toxicity/trauma.
  • may present at any time and may change over time
  • usually blue-yellow
  • sometimes treatable
  • pathological
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19
Q

Types of cones

A
  • blue(s)-shorter wavelength
  • green(m)
  • Red(l)- longer wavelength
20
Q

Rods

A

-do not preferentially detect light of certain wavelengths, but have a specific photopigment that detects light better in dim conditions

21
Q

Normal Trichromats

A

have normally functioning cones of all types

22
Q

Anomalous trichromats

A

-functional cones of all three types, but one type is sensitive to a different wavelength of light than normal.

23
Q

Dichromats

A

have only two types of functional photopigments

24
Q

Monochromats

A

have only one type of photopigment

  • only rods or a single type of cone function normally
  • rod and cone monochromats exist
25
Protanopia
dichromats that lack L-cone | "red blind"
26
Protanomalous
anomalous trichromats with functioning L-cone that is abnormal in sensitivity to red "red weak"
27
Deuteranopia
Lack of M-cone | "green blind"
28
Deuteranomalous
functioning M-cone that is abnormal in sensitivity to green | "green weak"
29
Tritanopia
lacking S-cone | "blue blind"
30
Tritanomalous
Functioning S-cone that has abnormal senstivity to blue | "blue weak"
31
X-linked inheritance
L and M cone photopigment genes
32
Autosomal inheritance
rod and S cone pigment genes
33
Chromatopsia
abnormal condition in which toxicity causes objects to be seen in a particular color of seem tinged in that color
34
What are the three things color vision tests specify?
1. lighting 2. viewing time 3. test distance
35
General guidelines for color testing
1. patients SHOULD wear corrective lenses 2. each eye is tested separately - unless just a screening - Unless occupation requires binocular 3. testing should be done before administering drugs or using instruments with bright lights 4. test should be stored in the dark to avoid fading 5. patients should use a brush to prevent oils from getting on the page
36
Pseudoisochromatic plate test (PIC)
- most common - quick and easy - screens for red-green defects
37
Types of PIC plate tests
1. transformation plates-person with color defect reads one figure and those with normal color see another 2. vanishing plates: person with color defect cannot read the figure seen by normal vision 3. hidden digit plate- person with normal vision fails to read a figure those with a defect can read 4. diagnostic plates-figure is readable by those with one type of defect but not by those with another
38
Arrangement tests
- measures type and severity of defect - can determine if defect is inherited or acquired - requires patient to place colors in a sequence based on hue, light, and saturation - order recorded by number on each sample - results are plotted and scored
39
Anomaloscopes
- most accurate - definitive diagnosis and quantifies condition - must rotate knobs for each side of a circle until they match in shade and color - expensive af and not used a lot
40
occupational vision requirements
driver-very few require color testing. need 20/40 pilot- color defect is okay, but depends on the type and severity BUT YOU CAN military- US military does not care. some specialties in the military care.
41
What kind of problems can VA detect?
- refractive error - optical media - retina, optic nerve - interpretive faculty of the brain - SOME DISORDERS CANNOT BE DETECTED BY VISUAL ACUITY
42
diffraction pattern
-eye is in ideal focus, point object image is on retina as small circular patch with faint surrounding rings
43
Optotype
test targets used for VA test
44
Minimum angle resolution
- expressed in minutes of arc - indicates the angular size of the critical detail within the just resolvable optotype - 20/200=10 minarc
45
Visual efficiency
- used when quantifying vision loss for legal and compensation purposes. - expanded to include losses of visual field and ocular motility
46
Measuring specifics
- typically check uncorrected first then corrected - right eye, left eye, both - can miss up to half of the letters in the line -ANYTIME YOU HAVE ABNORMAL VA, YOU HAVE TO ADDRESS IT IN YOU ASSESSMENT AND PLAN
47
ALTERNATIVE VA TESTS
- Visual evoked potentials- measures electric activity in brain - preferential looking tests-look towards the most interesting - optokinetic nystagmus- reaction and movement - Flash cards/symbols

OPT 514 (6 decks)

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