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FS Lectures > Ophthalmology: Introduction to Vision > Flashcards

Ophthalmology: Introduction to Vision Flashcards

1
Q

Define visual acuity

A

Resolving power of the eye

…minimum visible, separable, legible

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2
Q

The denominator in Snellen acuity indicates the distance (in feet) at which a letter will subtend…

A

…a visual angle of 5 minutes of arc

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3
Q

Functional vs Physiological VA limits

A

Functional = 20/10

Anatomical limits = 20/08 (single cone cell)

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4
Q

Which chart is used for VA qualifications for aviation applicants and designated aviation personnel?

A

“Good-Lite” (Sloan Magnetic Randomized Letter) Chart

Note: “Snellen” Eye Chart is the one typically seen in offices on the wall

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5
Q

Emmetropia

A

Standard refractive power and axial length…

  • aka refractive condition where parallel light rays focus on the retina when the eye is at rest…*
  • aka where the image of an object at 20ft focuses directly on the fovea*

“Normal”

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6
Q

Ametropic Eye

A

Non-standard refractive power or axial length

  • Excessive/insufficient power*
  • Longer/shorter axial length*
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7
Q

Myopia

A

“Nearsightedness”

A refractive condition in which light rays focus in front of the retina

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8
Q

Hyperopia

A

A refractive condition in which light rays focus behind the retina

“Farsightedness”

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9
Q

What causes myopia?

A

Excessive power (steeper cornea)

OR

Axial length is too long (“big eye”)

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10
Q

What causes hyperopia?

A

Deficient power (flatter cornea)

OR

Axial length is too short (“small eye”)

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11
Q

Which lenses correct myopia?

A

Minus lenses (diverging/concave)

Note: minus refers to negative focal point (aka left of lens)

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12
Q

Which lenses correct hyperopia?

A

Plus lenses (converging/convex)

Note: plus refers to positive focal length (right of lens)

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13
Q

Excessive refractive ametropia

A

aka excessive power = myopia

“nearsightedness”

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14
Q

Deficient refractive ametropia

A

aka Deficient Power = hyperopia

“farsightedness”

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15
Q

Axial Ametropia

A

Too long = myopia (nearsighted)

Too short = hyperopia (farsighted)

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16
Q

Define accommodation

A

The process of the lens changing its focusing power for near and far distances

Remember…ciliary body relaxed = zonules under tension

CB constricts = zonules relaxed = lens bulges = increased refractive power

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17
Q

True/False

Amplitude of accommodation is independent of age

A

False

  • Presbyopia = normal changes that lead to symptoms at age 40*
  • Pharmaceutical agents (atropine/cyclopentolate/tropicamide) and neurological (rare) causes can also lead to decreased accommodation*
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18
Q

Presbyopia

A

literally “old eyeballs”

Decreased accommodation with normal aging (symptomatic at about age 40)

18D at birth, less than 1D at age 65

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19
Q

Near objects focus ______ the retina in an unaccommodated eye

A

behind

Why presbyopia is corrected with plus lenses

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20
Q

Astigmatism

A

Light focusing in 2 spots due to 2 curvatures on the cornea and/or lens

“Multiple focal points”

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21
Q

Symptoms of Astigmatism

A
  • Reduced vision at distance/near
  • Elongated appearance of lights at night
  • Normal vision during the day, blurry at night
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22
Q

Correction for astigmatism

A

Cylindrical lenses (usually sphero-cylindrical)

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23
Q

True/False

Corneal Astigmatism shouldn’t dramatically change with age

A

True

Unlike lens astigmatism, which increases mildly with age

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24
Q

Lens power (in diopters) =

A

1 / f

  • f = focal length*
  • Note: lenses bend light, the numbers that describe a lens tell us how much they bend light and in what direction*
25
Q

In diopters, how much lens power is there when the focal lenth is 20cm?

A

+5.00 D

1/0.2m = 5

26
Q

Converging lenses can be used to correct…

A

… farsightedness (hyperopia)

designated by (+) for positive focal length

27
Q

Concave lenses can be used to correct for…

A

… nearsightedness (myopia)

Concave = diverging, designated at (-) lenses for negative focal length

28
Q

Spherical lenses bend light…

A

the same amount in all meridians (or axis)

Can be plus or minus

29
Q

Cylindrical lenses bend light…

A

in one meridian (or axis) only

30
Q

True/False

Most lenses have a combination of sphere and cylinder power

A

True

aka spherocylindrical lenses

31
Q

Anisometropia

A

Difference in refractive power between the eyes

Ex. OD -1.00 sph and OS +4.00 sph = 5.00 D aniso

32
Q

O.D.

33
Q

O.S.

34
Q

O.U.

35
Q

+

36
Q

-

A

concave (diverging)

37
Q

Visual Acuity from better to worse:

HM, NLP, PH, CF, LP

A

PH > CF > HM > LP > NLP

*Pinhole Acuity, Counts Fingers, Hand Motion, Light Perception, No LP

38
Q

DVA required for SNA applicants

A

Uncorrected 20/40-0 or better if corrected to 20/20-0

  • Remember…on a “GoodLite” chart*
  • Note: NVA has the same standards as DVA*
39
Q

True/False

There are no uncorrected DVA/NVA limits for SNFOs

40
Q

Refractive standards for SNA applicants

A

Spherical power limits: -1.50 to +3.00

No worse than -1.00 cylinder (astigmatism)

No worse than 3.50D anisometropia

41
Q

SNFO must correct to 20/___

A

20/20 -3 (7/10 letters in each eye*)

*GoodLite or AFVT

42
Q

SNFO Refractive Standards

A

Refraction no greater than + or - 8.00 D in any meridian

No more than 3.00 cylinder (astigmatism)

No worse than 3.50 anisometropia

43
Q

Aircrew applicant standards:

Uncorrected DVA (fixed vs rotary)

A

Fixed = no limit

Rotary = 20/100 uncorrected

Note: BOTH must correct to 20/20-3 on GoodLite or AFVT

44
Q

True/False

Aircrew applicants have no limit for refractive error

45
Q

Designated Class 1 Service Group 1

A

No platform limitations

  • Uncorrected DVA 20/100 (must correct to 20/20-0)*
  • No limit for refractive error*
  • Anisometropia must not exceed 3.50D*
46
Q

Designated Class 1 Service Group 2

A

Only restricted from fixed wing carrier ops

Uncorrected DVA 20/200 (must correct to 20/20-0)

No limit for refractive error

Anisometropia must not exceed 3.50D

47
Q

Designated Class 1 Service Group 3

A

Restricted from fixed wing carrier ops and flying without another SG1/SG2 pilot

Uncorrected DVA 20/400 (must correct to 20/20-0)

No limit for refractive error

Anisometropia must not exceed 3.50D

48
Q

Do designated Class III personnel enter aircraft

49
Q

Must carry extra pair of glasses if less than _____ uncorrected

A

20/100 uncorrected DVA (or less than 20/40 NVA)

50
Q

Stereopsis

A

Using both eyes for depth perception

Note: any history of strabismus surgery is considered disqualifying for pilots and rotary wing aircrew

51
Q

Phoria

A

When your eye has a “party position” (where it goes at rest)

Exophoria vs Esophoria

52
Q

Phoria standards for aviators

A

6 exo/eso

1.5 hyper

53
Q

NOTOSP

A

No Obvious heteroTropia or Symptomatic heteroPhoria

aka NOHOSH

54
Q

How much sensory input is visual?

55
Q

A 20/20 letter “E” at 20 feet is ______ mm high and subtends _____ minutes of arc

A

8.7mm high

5 minutes of arc

56
Q

A 20/200 letter “E” at 20 feet is _____ mm high and subtends _____ minutes of arc

A

87mm

50 min

57
Q

Bifocal addition is…

A

…the spherical power added to each eye

58
Q

Pupillary distance is measured in ______

A

millimeters

59
Q

Estimating Refractive Error:

20/10 =

20/20 =

20/40 =

20/200 =

A

20/10 = plano (zero)

20/20 = plano to -0.25

20/40 = -0.75

20/200 = -2.00 to -2.50

FS Lectures (9 decks)

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