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PPO 1 > Visual Acuity > Flashcards

Visual Acuity Flashcards

1
Q

What is Visual Acuity?

A

Visual keenness, sharpness of vision, and acuteness of vision.

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2
Q

True of False: VA is done everywhere including vision screenings, DMV, and during physical examination.

A

True.

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3
Q

What is VA measurement testing?

A

Every structure in the eye including cornea, lens, and retina. The entire neurological mechanism of vision. Brain structures underlying memory & cognition.

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4
Q

True or False: The strength of a chain is not determined by its weakest link. In order words, VA is not determined by the poorest functioning structure.

A

False.

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5
Q

What does it mean if the VA is normal? (Involving the chain)

A

It concludes that every structure making up the pathway is working normally.

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6
Q

What is Ametropia?

A

Faulty refraction of light rays by the eye.

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7
Q

What are three examples of Ametropia?

A

Myopia (nearsightedness), Hyperopia (farsightedness), and Astigmatism.

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8
Q

Does light focus behind the retina or in front of the retina in a myopic eye?

A

Light focuses in front of the retina on the “near side of the eye,” thus nearsightedness.

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9
Q

Does light focus behind the retina or in front of the retina in a hyperopic eye?

A

Light focuses behind the retina on the “far side of the retina,” this farsightedness.

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10
Q

True or False: During Astigmatism, light from a point object focuses as a single point but not as sharply.

A

False. Light from a point object does not focus as a single point; instead it focuses as two line images at different distances from the object.

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11
Q

VA involves Psychophysics. What is Psychophysics?

A

Involves brain and stimulus. It is the relationship between what someone sees, or says he sees, and a particular visual stimulus.

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12
Q

What are some accidental ways in which a patient may have reduced VA?

A

Patient may not care about trying. Patient cannot name the stimulus. Patient misunderstands directions. Patient is unable to respond. The patient cannot pay attention or is uncooperative.

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13
Q

What are the 4 types of VA?

A

Detection, Resolution, Recognition, and Direction.

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14
Q

What is detection?

A

Can the patient see that something is there.

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15
Q

What is resolution?

A

Can the patient distinguish the components of a complex stimulus that is detected.

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16
Q

What is recognition?

A

Can the patient identify or name the stimulus that he can both detect and whose parts he can resolve.

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17
Q

What is Direction?

A

Where is it.

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18
Q

True of False: Visual acuity measured during a screening is resolution VA.

A

True.

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19
Q

How is detection and recognition made very easy?

A

By making targets that are highly familiar and bright, and that has high contrast. Ex: Numbers, ABC’s, pictures.

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20
Q

True or False: The most commonly used and familiar VA test is based on the one published in 1862 called Landolt C.

A

False. It is the snellen system by Hermann Snellen.

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21
Q

How is physical size reported?

A

Physical size of objects is normally reported in millimeters or centimeter.

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22
Q

How is visual size measured?

A

Visual size is measured and reported in angular units (minarc= minute of arc).

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23
Q

True of false: Secarc=1/60 of a degree, minarc=1/360 of a circle, and degree=1/60 of a minarc.

A

False. Secarc=1/60 of a minarc, minarc=1/60 of a degree, and degree=1/360 of a circle.

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24
Q

True of False: The Snellen system tries to make both detection and recognition very easy, so that the VA we measure depends upon resolution.

A

True.

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25
Q

What is critical detail? What is its value?

A

Visual size of the lines that make up the letters. 1.0 minarc.

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26
Q

What is overall height? What is its value?

A

Top to bottom size of letter. 5 times the critical detail.

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27
Q

True of False: The visual size of the overall height of a basic target is 1.0 minarc.

A

False. critical detail X 5 = overall height.

1.0 minarc X 5 = 5.0 minarc.

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28
Q

What visual size can the standard observer recognize?

A

1 minarc critical detail and 5 minarc overall height. Therefore, the standard observer can recognize (detect and resolve) letters with the parameters of a “Basic Target”.

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29
Q

Is the standard observer considered normal?

A

Yes.

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30
Q

What is the standard test distance quantified at?

A

20 feet, or 6 meters, or 6000 millimeters.

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31
Q

True or False: The standard observer s able to recognize targets with the visual size of the basic target from the standard test distance.

A

True. The standard observer is able to recognize basic targets from a viewing distance of 20 feet.

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32
Q

If visual size of the overall height of a basic target is 1.0 minarc and the critical detail is 5.0 minarc, what is the PHYSICAL size of the overall height of a basic target and its critical detail?

A

Overall height of basic target= 8.73 mm
Critical detail= 1.7 mm
tan (0.0833)=opp/6000mm where opp=8.73mm is the over height. Overall height/5= 8.73mm/5= 1.7mm critical detail.

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33
Q

When VA is reduced below normal, what can you do?

A

Increase the visual size by moving the patient towards the chart or presenting larger targets.

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34
Q

True or False: When reduced VA occurs, it is easier to move the patient closer to the target than it is to increase the target size.

A

False. It is always easier and more practical to increase target size than have the patient move.

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35
Q

What are the rules for making larger targets when VA is worse than 20/20?

A

Increase the visual size by making sure letters go up in size in proportion and to make sure letter size is designated by the distance at which it would have the visual size of the basic target.

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36
Q

True or False: The standard observer cannot see a basic target if observing a 40 foot letter from 40 feet or even a 60 foot letter from 60 feet,

A

False. By definition, the standard observer can see a basic target; a 40 foot letter from 40 feet, a 60 foot letter at 60 feet, etc.

37
Q

Is 20 always going to be the numerator?

A

Yes. It is the testing distance.

38
Q

What does the denominator number mean?

A

Distance a “normal person can read the letters”.

Example: 20/60. What you see at 20 feet, a normal sees at 60 feet.

39
Q

What is the physical size in mm of the 60 foot letter?

A

8.73 mm/6000 mm = X mm/18000 mm

where X= 26.2 mm.

40
Q

Does the proportion process for finding the physical size of a letter work for all letters on a Snellen-type chart?

A

Yes.

41
Q

What is the physical overall height of a 100 foot letter in mm?

A

8.73 mm/20 ft = X mm/ 100 ft

where X= 43.65 mm.

42
Q

True or False: The proportion process works for all cases. If you increase the letter size or move the patient, you will still receive accurate results.

A

False. The proportion process works only as long as the chart is calibrated for a 6 meter or 20 feet viewing distance.

43
Q

True or False: If the test distance is other than 6 meters, then the physical size of the “20-foot” basic target is NOT 8.73 mm, even though it still retains the same visual size of the basic target.

A

True.

44
Q

What is the overall height of a Basic Target calibrated for a 4 meter room?

A

Step 1: 8.73 mm/6000 mm = X mm/4000 mm

where X= 5.82 mm.

45
Q

What is the overall height in mm of a 100-foot letter calibrated for a 10-foot viewing distance?

A

Step 1: 8.73 mm/20 ft = X mm/100 ft
where X= 43.65 mm
Step 2: 43.65 mm/20 ft = X mm/10 ft
where X= 21.82 mm.

46
Q

What would be the critical detail if the overall height of a 100-foot letter calibrated for a 10-foot viewing distance is 21.82 mm?

A

Critical detail= overall height/5

21.82 mm/5 = 4.36 mm.

47
Q

What is the overall height in mm of a 20/60 letter calibrated for 4-foot viewing distance?

A

Step 1: 8.73 mm/20 ft = X mm/60 ft
Where X= 26.2 mm
Step 2: 26.2 mm/20 ft = X mm/4 ft
Where X= 5.24 mm.

48
Q

What is the critical detail of a 20/80 letter?

A

20/80 means 4 times that of basic target critical detail.

(80/20) X 1.0 minarc= 4.0 minarc.

49
Q

What is the overall height of a 20/80 letter?

A

20/80 means 4 times that of basic target overall height.

(80/20) X 5 minarc= 20 minarc.

50
Q

True or False: A properly calibrated 20-foot letter, at any and all distances, always has a critical detail of 1 minarc and overall height of 5 minarc by definition.

A

True.

51
Q

What is the “Sweeping Generalization” when it comes to VISUAL size and finding its critical detail?

A

The reciprocal of the Snellen fraction is the visual size of the critical detail in minarc
(Because always multiplying by 1 minarc, making is so the reciprocal of say 20/60 is 3 minarc.).

52
Q

What is the visual size of the critical detail in minarc of a 20/40 letter calibrated for a reading distance of 40 cm?

A

(40/20) X 1 minarc= 2 minarc.

53
Q

What is the visual size of the overall height in minarc of a 20/40 letter calibrated for a reading distance of 40 cm?

A

(40/20) X 5 minarc= 10 minarc.

54
Q

What is the physical size of the overall height in mm of a 20/40 letter calibrated for a reading distance of 40 cm?

A

Step 1: 8.73 mm/ 20 ft = X mm/ 40 ft
Where X= 17.46 mm
Step 2: 17.46 mm/ 6000 m = X mm/ 400 m
Where X= 1.164 mm.

55
Q

The Snellen System has withstood the test of time, but it is not perfect. Name other VA systems used to test VA.

A

Tumbling E’s, Landolt C’s, Lea’s symbols.

56
Q

True or False: There is no relationship between vision and logarithm. That’s why Snellen system is the best.

A

False. The relationship between VISION and the ability to see almost anything almost always varies in proportion with the LOGARITHM of its physical dimensions, not its actual physical dimensions.

57
Q

True or False: Scientists developed an eye chart system that still required patients to read the smallest target they can but instead of interpreting results like the Snellen system, it was interpreted as the patient’s Minimum Angle of Resolution (MAR) and expressed as a Logarithm base 10 (Log). “LogMAR”

A

True.

58
Q

What is the LogMAR of a 20/20 target?

A

MAR is 1.0 minarc.

Log(10) of 1.0 minarc= 0 (on calculator its Log(1).

59
Q

What is the LogMAR of a 20/80 target?

A 
MAR is (80/20) X 1 minarc= 4 minarc.
Log(10) of 4.0 minarc= 0.60 ( on calculator its Log(4).
60
Q

What is the Snellen equivalent of a target with LogMAR of +0.20?

A

Step 1: MAR= 10^+0.2= 1.58
Step 2: MAR= X/20 (this being the reciprocal of Snellen fraction with 20 always being the numerator)
1.58= X/20 where X= 31.7
Snellen equivalent= 20/32.

61
Q

What is the Snellen equivalent of a target with LogMAR of +0.70?

A

Step 1: MAR= 10^+0.7= 5.01
Step 2: MAR= X/20 (this being the reciprocal of Snellen fraction with 20 always being the numerator)
5.01= X/20 where X= 100.2
Snellen equivalent= 20/100.

62
Q

What are some things you need to remember for a LogMAR-Snellen transition?

A

LogMAR of 0.00 if always Snellen’s 20/20.
IMPORTANT: LogMAR VAs are positive/negative sensitive. Sometimes LogMAR VA chart match up exactly to Snellen (20/40=0.30) and others don’t (20/63=0.50)

63
Q

True or False: In the 21st Century, LogMAR is considered to be “better” than systems based solely on proportional physical size .

A

True.

64
Q

What are some examples of charts that use LogMAR?

A

All federally funded research projects that take and report VA, ETDRS (Early Treatment of Diabetic Retinopathy Study), and Lea symbols for preschoolers.

65
Q

CSL: True or False: The result of a VA screening is “pass” or “fail”.

A

False. Pass or refer.

66
Q

CSL: Should you refer a child under the age of 6 if he has 20/50 or worse VA in either eye?

A

Yes, refer.

67
Q

CSL: Should you refer a child age 6 and older if he has 20/40 or worse VA in either eye?

A

Yes, refer.

68
Q

CSL: True or False: For children of all ages, you do not have to refer if there is a difference in VA between the eyes by 2 lines or more.

A

False. You must refer children of all ages having a difference in VA between the eyes by 2 lines or more.

69
Q

CSL: Do you have to refer a student if there is a manifestation of significant signs or symptoms that suggest a visual difficulty?

A

Yes. Such symptoms include student’s behavior, complaints, appearance, performance, or physical activity.

70
Q

CSL: True of False: California State Law only addresses distance vision.

A

True.

71
Q

CSL: Should you screen a child if he has glasses?

A

Yes. He should be screened WITH the glasses on at the distance the glasses were intended to be used. (i.e. screen near VA with reading glasses).

72
Q

CSL: If the VA chart has 5 letter, how many does the student need to answer correctly in order to pass?

A

3 or more. More than half.

73
Q

CSL: If the VA chart has 4 letter, how many does the student need to answer correctly in order to pass?

A

3 or more. More than half.

74
Q

CSL: If the VA chart has 3 letter, what is the least amount of letters the student is allowed to miss in order to still pass?

A
  1. Must answer half or more to pass. In this case, student must answer 2 or more to pass.
75
Q

CSL: If a student’s VA OD is 20/30 and VA OS is 20/20, would this be a pass or a refer?

A

Refer. Refer means there is at least a 2 line difference between the eyes. In this case, there is a 2 line difference.

76
Q

CSL: If a student’s VA OD is 20/30 and VA OS is 20/25, would this be a pass or a refer?

A

Pass. This student has less than a 2 line difference between the eyes. In this case, there is a 1 line difference.

77
Q

CSL: If a student’s VA OD is 20/40 and VA OS is 20/30, would this be a pass or a refer?

A

Pass. It goes 20, 25, 30, 40, 50… and so on. In this case, there is only a 1 line difference.

78
Q

What are some techniques a student doctor must do at a Vision Screening?

A

Always observe patients eyes. Make certain only one eye is tested at a time. Make sure there is no squinting. Encourage students to try their hardest. Make sure there are no reflections or shadows on the chart.

79
Q

What are the 3 reasons to refer a student at a Vision Screening?

A
  1. Reduced vision
  2. Differences in VA between the eyes of two or more lines
  3. Manifestation of significant signs or symptoms.
80
Q

True or False: Vision Screening determines why the VA is reduced.

A

False. VA is a complex behavior that includes a chain of things.

81
Q

What are the most common causes of reduced VA in children?

A

Ametropia (images out-of-focus), Amblyopia (non-pathology reduced VA), and child’s uncooperativeness.

82
Q

What is Amblyopia? What are the two things that often is associated with Amblyopia?

A

It is reduced VA even with the best spectacle prescription in place and a healthy eye. It is often associated with strabismus (lazy eye or eye turn) or anisometropia.

83
Q

How is anisometropia defined?

A

Unequal amount of ametropia (refractive error) between the two eyes.

84
Q

True of False: Anisometropia may cause reduced vision in one eye and may cause asthenopia (eye discomfort).

A

True. It can also lead an individual to have difficulty with near work, contribute to poor reading skills and poor school performance. (asthenopia= eye discomfort)

85
Q

Does anisometropia exist if the amount of hyperopia is slightly different in the two eyes?

A

Depends. If there is a significantly different amounts of hyperopia in the two eyes, for instance OD +5 and OS +1, most likely anisometropia exists and child may be at risk for amblyopia.

86
Q

A child with low to moderate amounts of hyperopia that is equal in both eyes may still have difficulty with what?

A

Asthenopia (eye discomfort), poor reading ability, poor school performance.

87
Q

What test do we use to test uncorrected low or moderate hyperopia? What’s pass and refer?

A

Plus Lens Test on an isolated 20/30 line. +2.50 lenses used.
Able to read line with +20/30 lens= REFER
Unable to read line with +20/30 lens= PASS.

88
Q

True or False: Plus lenses correct myopia.

A

False. Plus lens correct hyperopia.

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