Astigmatism 1, Astigmatism 2 And Presbyopia Flashcards by Rubia Paola Villarin

First accurate description of astigmatism as such credited in 1800

Thomas young

How well did you know this?

Not at all

Perfectly

Were reported in a period of nearly seventy years

11 cases

How well did you know this?

Not at all

Perfectly

First one to produce a distance test chart for astigmatism

John Green

How well did you know this?

Not at all

Perfectly

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

ASTIGMATISM

How well did you know this?

Not at all

Perfectly

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

Causes of astigmatism

How well did you know this?

Not at all

Perfectly

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

Corneal astigmatism

How well did you know this?

Not at all

Perfectly

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

Direct or with the rule astigmatism

How well did you know this?

Not at all

Perfectly

What is with the rule astigmatism

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

How well did you know this?

Not at all

Perfectly

Lens

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

How well did you know this?

Not at all

Perfectly

Other cause of astigmatism

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

How well did you know this?

Not at all

Perfectly

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

Fovea

How well did you know this?

Not at all

Perfectly

Changes may occur in the _____ with resultant variation index

Vitreous gel

How well did you know this?

Not at all

Perfectly

_____ surface may exhubit some irregularity

Fundus

How well did you know this?

Not at all

Perfectly

How is astigmatism diagnosed

Visual acuity
Keratometry
Refraction
Retinoscopy

How well did you know this?

Not at all

Perfectly

-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

Total astigmatism

How well did you know this?

Not at all

Perfectly

Total astigmatism

Anterior cornea + residual

How well did you know this?

Not at all

Perfectly

Residual

Posterior corneal surface
Lenticular surface
Lenticular zonule

How well did you know this?

Not at all

Perfectly

Complete anatomical data

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

How well did you know this?

Not at all

Perfectly

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

Corneal astigmatism

How well did you know this?

Not at all

Perfectly

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

Regular

How well did you know this?

Not at all

Perfectly

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

Irregular

How well did you know this?

Not at all

Perfectly

Referred to each cornea

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

How well did you know this?

Not at all

Perfectly

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

Oblique

How well did you know this?

Not at all

Perfectly

Referred to each cornea

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

How well did you know this?

Not at all

Perfectly

Referred to both cornea

Symmetric Homologous Heterologous

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

Symmetric

Homologous

If with-the-rule

Heterologous

If against-the-rule

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

Asymmetric

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

Homonymous

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

Heteronymous

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

Lenticular

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

S.H.A Simple hyperopic astigmatism

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

C.h.a Compound hyperopic astigmatism

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

S.M.A SIMPLE MYOPIC ASTIGMATISM

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

C.M.A COMPOUND MYOPIC ASTIGMATISM

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

M.A MIXED ASTIGMATISM

Something different from another of the same type

Variation

Change at near In amount According to

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

So called with the rule form of astigmatism according to

Beau seigneur (1946)

Causes of lenticular astigmatism

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

Stenopaic effect

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

To conclude the investigation by the different investigators

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

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

Scobee (1947) reported 75%

The medical science of symptoms The combined symptoms of a disease

Symptomatology

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

Subjective

A symptom evident to the observer Or a sign

Objective

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

ASTHENOPIA

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

Basic correction

Following consideration

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

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

Spherical equivalent

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

Spherical equivalent

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

ASTIGMATISM

Has an unequal curvature on its anterior surface

Cornea

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

Lens

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

Amount of astigmatism

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

Classifications

When the cornea has unequal curvature On the anterior surface

Corneal astigmatism

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

Corneal astigmatism

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

Lenticular astigmatism

The sum of corneal astigmatism and residual astigmatism

Total astigmatism

Corneal+ residual

Residual

PCS POSTERIOR CORNEAL SURFACE LS LENTICULAR SURFACE LZ LENTICULAR ZONULE

When the two principal meridians are perpendicular to each other

Regular astigmatism

The three types of regular astigmatism

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

With-the-rule astigmatism

Minus cylinder axis around horizontal meridian

-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

With-the-rule astigmatism

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

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

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

Oblique astigmatism

-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

IRREGULAR ASTIGMATISM

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

Simple astigmatism

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

Simple myopic astigmatism

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

Simple hyperopic astigmatism

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

Compound astigmatism

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

Compound myopic astigmatism

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

Compound hyperopic astigmatism

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

Mixed astigmatism

-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

Symmetrical astigmatism

-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

Asymmetrical astigmatism

-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

Age

In general there are no significant differences between males and females

Gender

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

Ethnicity

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

General trend

-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

VISUAL ACUITY

Accommodation may make the retinal image even more blurry

Simple or compound myopic astigmatism

Accommodation may improve VA ti some extent

Simple or compound hyperopic astigmatism

-Va is relatively good -may not need much accommodations

Mixed astigmatism

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

Spherical refractive error (D)

Decreased visual acuities at distance or near

Signs

-clinical test -Distance and near

Visual acuity test -autorefraction -keratometry -retinoscopy

Most reliable source of information for cylinder power or axis

Retinoscopy

Single vision glasses with cylinder

Spectacles

-toric soft -toric rigid gas permeable contact lenses

Contact lenses

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

Refractive surgery

Another term of presbyopia

Short arm syndrome

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

PRESBYOPIA

Presbyopia age start

40-50

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

Presbys-old Ops-eye

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

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

Muscle based The amount of ciliary muscle contraction

D-D-F Donder' s-Duane-Fincham theory

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

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

Causes of sclerosis

Nutritional changes Action uv rays Exposure to intense infrared radiation

Astigmatism 1, Astigmatism 2 And Presbyopia Flashcards

(102 cards)