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Intro To Opto > Astigmatism 1, Astigmatism 2 And Presbyopia > Flashcards

Astigmatism 1, Astigmatism 2 And Presbyopia Flashcards

1
Q

First accurate description of astigmatism as such credited in 1800

A

Thomas young

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2
Q

Were reported in a period of nearly seventy years

A

11 cases

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3
Q

First one to produce a distance test chart for astigmatism

A

John Green

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4
Q

Defined as a refractive condition in which a variation of power exists in different meridians of the eye

A

ASTIGMATISM

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5
Q

The posterior principal foci of the same eye vary cause is almost always ba difference in curvature of the refractive surface of the ocular meridian

A

Causes of astigmatism

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6
Q

The major surface which can be proven to exhibit such a discrepancy is the anterior surface of the cornea unequal curvsture of the cornea

A

Corneal astigmatism

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7
Q

The major source of Astigmatism is held to be anterior surface of cornea,which usually exhibits

A

Direct or with the rule astigmatism

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8
Q

What is with the rule astigmatism

A

Different types of astigmatism are classified based on the shape of the cornea,lens and principal meridians. With the rule astigmatism is a common form of astigmatism that causes the cornea to be oblong shaped with high refractive power in the vertical meridian

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9
Q

Lens

A

The major astigmatic effect of the lens is not attributed to unequal curvature but not potentiality of the lens to be tilted in relation to the visual axis or shifted position within the eye

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10
Q

Other cause of astigmatism

A

Traction of the external ocular muscles upon the eyeball may force the sclera into a toroidal shape without altering the cornea

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11
Q

The eye may occupy an eccentric position in relation to the visual axis

A

Fovea

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12
Q

Changes may occur in the _____ with resultant variation index

A

Vitreous gel

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13
Q

_____ surface may exhubit some irregularity

A

Fundus

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14
Q

How is astigmatism diagnosed

A

Visual acuity
Keratometry
Refraction
Retinoscopy

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15
Q

-The sum resultant astigmatism of all factors of REFRACTIVE system due to normal variations in the surface of the different media
-also called physiological by duke elder

A

Total astigmatism

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16
Q

Total astigmatism

A

Anterior cornea + residual

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17
Q

Residual

A

Posterior corneal surface
Lenticular surface
Lenticular zonule

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18
Q

Complete anatomical data

A

A.C
ANTERIOR CORNEA
P.C
POSTERIOR CORNEA
F.C.P
FULL CORNEA PACHYMETRY
A.C.D
ANTERIOR CORNEA DEPTH
I
IRIS
L
LENS

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19
Q

In which the cornea exhibits a variation of curvature throughout different meridians

A

Corneal astigmatism

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20
Q

In which two principal meridians exist at right angle to each other one of the greatest and one of the least curvature

A

Regular

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21
Q

In which either the two principal axis are not at right angles to each other or the curvature of any one meridian is not uniform

A

Irregular

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22
Q

Referred to each cornea

A

With-the-rule (direct)
Against-the-rule (inverse or perverse)
Oblique

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23
Q

The meridian of greatest curvature lies between 30th to 60th or the 120th to 150th meridian

A

Oblique

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24
Q

Referred to each cornea

A

Wtr
With-the-rule (diect)
Against-the-rule (inverse or perverse)
Oblique

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25
Q

Referred to both cornea

A

Symmetric
Homologous
Heterologous

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26
Q

The total of the degrees representing the two weakest ( or two strongest) meridians for both eyes equals 180 degrees

A

Symmetric

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27
Q

Homologous

A

If with-the-rule

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28
Q

Heterologous

A

If against-the-rule

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29
Q

When two weakest or the two strongest meridians of both eyes do not total 180 degrees upon additin of their meridional locations

A

Asymmetric

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30
Q

Both eyes are with-the-rule or both are against-the-rule

A

Homonymous

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31
Q

One eye is with-the-rule and the others is against-the-rule

A

Heteronymous

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32
Q

In which the astigmatism is due to unequal curvature of the lens surface or layers

A

Lenticular

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33
Q

With accommodation relaxed, one meridian would focus on the retina while the other would tend to focus behind the retina

A

S.H.A
Simple hyperopic astigmatism

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34
Q

With the ACCOMMODATION completely relaxed the posterior principal foci of both meridians would tend to fall beyond the retina

A

C.h.a
Compound hyperopic astigmatism

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35
Q

With accomodation relaxed one meridian would focus on the retina and the other would focus in front of the retina

A

S.M.A
SIMPLE MYOPIC ASTIGMATISM

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36
Q

With accomodation relaxed,both principal meridians focus in front of the retina

A

C.M.A
COMPOUND MYOPIC ASTIGMATISM

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37
Q

With accomodation relaxed one meridian tends to focus behind the retina,while the other focuses in front of the retina

A

M.A
MIXED ASTIGMATISM

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38
Q

Something different from another of the same type

A

Variation

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39
Q

Change at near
In amount
According to

A

Mcdowell (1924)
Cox (1938)
Marton (1942)
Pascall (1944)

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40
Q

So called with the rule form of astigmatism according to

A

Beau seigneur (1946)

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41
Q

Causes of lenticular astigmatism

A

Such as tilt of the lens and the action extrinsic muscles maybe aggravated by accommodative action.

42
Q

Stenopaic effect

A

Lids when narrowed for near work and the diminution of the size of the pupil may also decrease the aberrations of the refractive system

43
Q

To conclude the investigation by the different investigators

A

A. Spherical effect upon the astigmatism of the accommodations or spherical lens.
B.variations of effectivity of the correcting lens with changes in distance of fixation,power of the eye and incidence of the source

44
Q

Revealed that the shift axis of the correcting cylinder which he believed to be due lenticular changes

A

Scobee (1947) reported 75%

45
Q

The medical science of symptoms
The combined symptoms of a disease

A

Symptomatology

46
Q

Symptoms that are observed only by the patients and that cannot objectively observed

A

Subjective

47
Q

A symptom evident to the observer
Or a sign

48
Q

This may be due to the requirement for constant accommodation in an attempt to place the circle of least confusion on the retina and to subsidiary wrinkling and furrowing of the brows the narrowing of the pupil aperture to reduce aberration and the assumption of unnatural ocular postures in cases of oblique astigmatism

A

ASTHENOPIA

49
Q

For Astigmatism consists of the cylindrical power which equalizes the discrepancy between the two principal meridians

A

Basic correction

50
Q

Following consideration

A

Effect upon image
Previous adaptation
Different amount of astigmatism at near point than existed at the far point

51
Q

Cylinders apparently cannot be worn or where mixed astigmatism has been found and the patient shows no preference for the cylindrical correction.

A

Spherical equivalent

52
Q

The asthenopia may be relieved by the relaxation of the accomodation which the patient has been using to place the circle of least confusion on the retina, which are 45 degrees from the principal meridians upon the retina every spherocylindrical combination which leaves those meridian upon the retina

A

Spherical equivalent

53
Q

When parallel rays of light enter the eye with accommodation relaxed and do not come to a single point focus on or near the retina

A

ASTIGMATISM

54
Q

Has an unequal curvature on its anterior surface

55
Q

Crystalline lens has an unequal curvature on its surface or in its layers

56
Q

Equal to the difference in refracting power of the two principal meridians

A

Amount of astigmatism

57
Q

Based on relative locations of principal meridians or axes when comparing the two eyes

A

Classifications

58
Q

When the cornea has unequal curvature On the anterior surface

A

Corneal astigmatism

59
Q

When the crystalline lens has an unequal curvature on the anterior surface

A

Corneal astigmatism

60
Q

When the crystalline lens has an unequal curvature on the surface or in its layers

A

Lenticular astigmatism

61
Q

The sum of corneal astigmatism and residual astigmatism

A

Total astigmatism

62
Q

Total astigmatism

A

Corneal+ residual

63
Q

Residual

A

PCS
POSTERIOR CORNEAL SURFACE
LS
LENTICULAR SURFACE
LZ
LENTICULAR ZONULE

64
Q

When the two principal meridians are perpendicular to each other

A

Regular astigmatism

65
Q

The three types of regular astigmatism

A

WTR
With-the-rule,
ATR
AGAINST-THE-RULE
AND OBL
OBLIQUE ASTIGMATISM

66
Q

With-the-rule astigmatism

A

Minus cylinder axis around horizontal meridian

67
Q

-When greatest refractive power is within 030 of the horizontal meridian (i.e between 0 and 30,150 and 180 meridians)
-the most common type of astigmatism based on the orientation of meridians

A

With-the-rule astigmatism

68
Q

When the greatest refractive power is within 030 of the vertical meridian (i.e between 060 to 120 meridians)

A

Against-the-rule astigmatism (Atr)
Minus cylinder axis around vertical meridian

69
Q

When the greatest refractive power is within 030 of the oblique meridians (i.e between 030 and 060 or 120 and 150)

A

Oblique astigmatism

70
Q

-When the two principal meridians are not perpendicular to each other.
-curvature of any one meridian is not uniform
-associated with trauma disease or degeneration.
-VA is often not correctable to 20/20

A

IRREGULAR ASTIGMATISM

71
Q

When one of the principal meridians is focused on the retina and the other is not focused on the retina (with accommodation relaxed)

A

Simple astigmatism

72
Q

When one of the principal meridians is focused in front of the retina and the other is focused on the retina (with accommodation relaxed)

A

Simple myopic astigmatism

73
Q

When one of the principal meridians is focused behind the retina and the other is focused in front on the retina (with accommodation relaxed)

A

Simple hyperopic astigmatism

74
Q

When both principal meridians are focused either front or behind the retina (with accommodation relaxed)

A

Compound astigmatism

75
Q

When both principal meridians are focused in front of the retina (with accommodation relaxed)

A

Compound myopic astigmatism

76
Q

When both principal meridians are focused behind the retina (with accommodation relaxed)

A

Compound hyperopic astigmatism

77
Q

When one of the principal meridians is focused in front of the retina and the other is focused behind the retina (with accommodation relaxed)

A

Mixed astigmatism

78
Q

-The principal meridians or axes of the two eyes are symmetrical (e.g both eyes are WTR OR ATR)
-the sum of two axes of the two eyes equals approximately 180

A

Symmetrical astigmatism

79
Q

-The principal meridians or axes of the two eyes are not symmetrical (e.g one eye is wtr while the other eye is ATR)
-THE SUM of the two axes of the two eyes does not equal approximately 180

A

Asymmetrical astigmatism

80
Q

-infants are born with atr astigmatism where the cornea is the source of the astigmatism
- preschool children have little or no astigmatism
-teenage children demonstrate a shift towards wtr astigmatism
- older adults show a shift towards atr astigmatism

81
Q

In general there are no significant differences between males and females

82
Q

-higher prevalence in north Americans,latinos
-asian infants tend to be WTR astigmatism
-caucasian infants tend to be ATR astigmatism

83
Q

For older adults the average rate of change towards atr astigmatism is less than or equal to 0.25D every 10 yrs

A

General trend

84
Q

-Theoretically at no distance does an uncorrected astigmat have a sharp retinal image.
-clinically if astigmatism is small (less than 0.50DC) the patient may not notice blur

A

VISUAL ACUITY

85
Q

Accommodation may make the retinal image even more blurry

A

Simple or compound myopic astigmatism

86
Q

Accommodation may improve VA ti some extent

A

Simple or compound hyperopic astigmatism

87
Q

-Va is relatively good
-may not need much accommodations

A

Mixed astigmatism

88
Q

-myopia or absolute hyperopia
-when multiplied by a factor of two it equals astigmatism (D)

A

Spherical refractive error (D)

89
Q

Decreased visual acuities at distance or near

90
Q

-clinical test
-Distance and near

A

Visual acuity test
-autorefraction
-keratometry
-retinoscopy

91
Q

Most reliable source of information for cylinder power or axis

A

Retinoscopy

92
Q

Single vision glasses with cylinder

A

Spectacles

93
Q

-toric soft
-toric rigid gas permeable contact lenses

A

Contact lenses

94
Q

-photorefractive keratometry (prk)
-laser assisted in situ keratomileusis (Lasik)

A

Refractive surgery

95
Q

Another term of presbyopia

A

Short arm syndrome

96
Q

The inability of the human eye to focus on objects up close that result with aging.

A

PRESBYOPIA

97
Q

Presbyopia age start

98
Q

A condition whereby the amplitude of accomodation diminishes when increase in age where clear and comfortable vision at near point is not achievable. Recession of near point with increase in age

A

Presbys-old
Ops-eye

99
Q

Lens based
Attributes all of the loss in acc to biomechanical changes in the lens capsule and lens and none to the ciliary muscle the amount of ciliary muscle contraction (or effort/innervation) required to produce a unit change in acc. Remains contact with age

A

H-H-G THEORY
HELMHOLTZ- HESS-GULLSTRAND THEORY

100
Q

Muscle based
The amount of ciliary muscle contraction

A

D-D-F
Donder’ s-Duane-Fincham theory

101
Q

Muscle based
The amount of ciliary muscle contraction needed to produce a unit change in acc progressively increases with age thus as one ages the reduced amplitude is due to progressive weakening of the ciliary muscle itself

A

D-D-F
Donder’ s-Duane-fincham theory
Muscles based

102
Q

Causes of sclerosis

A

Nutritional changes
Action uv rays
Exposure to intense infrared radiation

Intro To Opto (9 decks)

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