astigmatism_2.ppt

Astigmatism is a type of refractive error Astigmatism is a type of refractive error

wherein the refraction varies in the wherein the refraction varies in the different meridian.different meridian.

Astigmatism is aAstigmatism is a defect in which light defect in which light

entering the eye is unable to be brought to entering the eye is unable to be brought to

a single focus on retina resulting in blurred a single focus on retina resulting in blurred

vision at all distances. vision at all distances.

It simply means that there is a It simply means that there is a variation variation

and disturbance in the shape of the and disturbance in the shape of the

cornea or lens. It is usually due to an cornea or lens. It is usually due to an ––

**Irregularly shaped corneaIrregularly shaped cornea

* * Scarring of the corneaScarring of the cornea

*Abnormities in the crystalline lens*Abnormities in the crystalline lens

**Some eyes conditions are seen along **Some eyes conditions are seen along with astigmatism as with astigmatism as

NystagmusNystagmusCataractCataractPtosis Ptosis Retinitis pigmentosa Retinitis pigmentosa Albinism Albinism Inflammation Inflammation degenerationdegeneration

Symptoms:-Symptoms:-

Eye strainEye strain discomfortdiscomfort headacheheadache dry eyedry eye sensitivity to lightsensitivity to lightBlurred vision Blurred vision

Classification of astigmatism

Physiology Pathological

regular Irregular

compoundsimple mixed

myopic hypermetropicWith the rule

Against the rule

Hypermetropic myopic

With the rule

Against the rule

With the rule

Against the rule

With the rule

Against the rule

With the rule

Against the rule

Type of astigmatism :-Type of astigmatism :-

there are two type of astigmatism:-there are two type of astigmatism:-

1.1. Regular astigmatism Regular astigmatism

2.2. Irregular Irregular astigmatism astigmatism

Regular astigmatismRegular astigmatism

The astigmatism is regular when the The astigmatism is regular when the refractive power changes uniformly refractive power changes uniformly from one meridian to another from one meridian to another

A etiology :-A etiology :-

1.1. Corneal astigmatism Corneal astigmatism

2.2. Lenticular astigmatism Lenticular astigmatism

3.3. Retinal astigmatism Retinal astigmatism

corneal astigmatism corneal astigmatism

it is the result of abnormality of it is the result of abnormality of

curvature of corneacurvature of cornea It is usually congenitalIt is usually congenital acquired corneal astigmatism is acquired corneal astigmatism is

often irregular often irregular

CausesCauses CongenitalCongenital curvature astigmatism curvature astigmatism KeratoconousKeratoconous Trauma to the cornea or lens Trauma to the cornea or lens After cataract operation After cataract operation

Lenticular astigmatismLenticular astigmatism

Mainly due to Mainly due to

*congenital abnormality of lens *congenital abnormality of lens

*re*refractive index of lens fractive index of lens

*congenital or traumatic subluxation *congenital or traumatic subluxation of the lens of the lens

Retinal astigmatismRetinal astigmatism

*Due to oblique placement of macula *Due to oblique placement of macula

* It can be corrected by visual aid* It can be corrected by visual aid

type of regular astigmatism type of regular astigmatism

It is subdivided into four type ;It is subdivided into four type ;––With-the-rule astigmatismWith-the-rule astigmatismAgainst-the-rule astigmatismAgainst-the-rule astigmatismOblique astigmatismOblique astigmatism bi-oblique astigmatism bi-oblique astigmatism

With-the-rule astigmatismWith-the-rule astigmatism : :

Refractive power of the vertical Refractive power of the vertical meridian is greatest meridian is greatest

.The vertical meridian is steepest than .The vertical meridian is steepest than horizontal meridian.horizontal meridian.

Eyes see vertical lines more sharply Eyes see vertical lines more sharply than horizontal lines. than horizontal lines.

Requires concave cylinders at 180+ /-Requires concave cylinders at 180+ /-2020

Or convex cylinders at 90+/-20 Or convex cylinders at 90+/-20 degrees degrees

Against-the-rule astigmatismAgainst-the-rule astigmatism : :

the refractive power of horizontal the refractive power of horizontal meridian is greatest than vertical meridian is greatest than vertical meridian.meridian.

Horizontal meridian is steepest than Horizontal meridian is steepest than vertical meridian.vertical meridian.

Eyes see horizontal lines more sharply Eyes see horizontal lines more sharply than vertical lines.than vertical lines.

Requires concave cylinders at 90 +/-Requires concave cylinders at 90 +/-20degrees20degrees

Or convex cylinders at 180+/-20 degrees.Or convex cylinders at 180+/-20 degrees.

Oblique astigmatismOblique astigmatism::

In which the two principle meridians In which the two principle meridians lies somewhere between the axis lies somewhere between the axis defining either with-the-rule or defining either with-the-rule or against-the-rule astigmatism. against-the-rule astigmatism.

Complementary (45 in one Complementary (45 in one meridian,135 in other meridian)meridian,135 in other meridian)

Bi Bi ––oblique astigmatismoblique astigmatism

Principle meridian are not at right Principle meridian are not at right angle angle

One at 30 , other at 100 One at 30 , other at 100

optics of regular astigmatismoptics of regular astigmatism

Light entering the eye cannot converge to Light entering the eye cannot converge to

a point focus but form focal lines a point focus but form focal lines Configuration of rays refracted from the Configuration of rays refracted from the

astigmatic surface astigmatic surface ––( sturms conoid) .( sturms conoid) .Lens with cylinder produces an astigmatic Lens with cylinder produces an astigmatic

focus .this astigmatic focus contains focus .this astigmatic focus contains vertical line ,corresponding to the focus of vertical line ,corresponding to the focus of the horizontal principal meridian .and the horizontal principal meridian .and horizontal focal line corresponding to the horizontal focal line corresponding to the focus of the vertical principal meridian .focus of the vertical principal meridian .

The region between these two lines The region between these two lines is known as the conoid of sturm .is known as the conoid of sturm .

At the dioptric At the dioptric mid mid ––point between point between these two focal line , the astigmatic these two focal line , the astigmatic focus forms a circular patch known focus forms a circular patch known as circle of least confusion as circle of least confusion

a. Simple hypermetropia astigmatism a. Simple hypermetropia astigmatism

When refracted rays from one When refracted rays from one meridian takes focus on the retina meridian takes focus on the retina and refracted rays from other and refracted rays from other meridian takes focus behind the meridian takes focus behind the retina.retina.

b)Simple myopic astigmatismb)Simple myopic astigmatism

When refracted rays from one When refracted rays from one meridian takes focus on the retina meridian takes focus on the retina and refracted rays from other and refracted rays from other meridian takes focus in front of meridian takes focus in front of retina. retina.

c) Compound hypermetropic c) Compound hypermetropic astigmatismastigmatism::

In this condition of astigmatism refracted In this condition of astigmatism refracted rays from both meridians take focus rays from both meridians take focus behind the retinabehind the retina..

d) d) Compound myopic astigmatism:Compound myopic astigmatism:

In this condition of astigmatism In this condition of astigmatism refracted rays from both meridians refracted rays from both meridians take focus in front of retina.take focus in front of retina.

e)e) Mixed astigmatismMixed astigmatism:: When When refracted rays from one meridian refracted rays from one meridian take focus in front of retina and take focus in front of retina and refracted rays from other meridian refracted rays from other meridian take focus behind the retina. take focus behind the retina.

b) Irregular astigmatismb) Irregular astigmatism:: Irregular differences in curvature or Irregular differences in curvature or

refractive index of the optic refractive index of the optic components or misalignment of any components or misalignment of any optical component may lead to optical component may lead to irregularity.irregularity.

It is often the result of trauma,It is often the result of trauma, pterygium,pterygium, corneal scars, corneal scars, and complication of refractive surgery.and complication of refractive surgery. Another not uncommon condition is Another not uncommon condition is

conical cornea (keratoconous)conical cornea (keratoconous)

DiagnosticDiagnostic ObjectivelyObjectively:: With the help of retinoscopyWith the help of retinoscopyAutorefractometerAutorefractometerKeratometerKeratometerCorneal topography Corneal topography SubjectivelySubjectively::By JacksonBy Jackson’’s cross cylinders cross cylinderBy astigmatic fanBy astigmatic fanBy stenopaeic slit By stenopaeic slit

managementmanagement

CONSERVATIVECONSERVATIVE MANAGEMENTMANAGEMENT:: Prescription eye wearPrescription eye wear Spherical soft contact lensesSpherical soft contact lenses Spherical RGP contact lensesSpherical RGP contact lenses Toric soft contact lensesToric soft contact lenses

SURGICAL MANAGEMENTSURGICAL MANAGEMENT

1.1. Conventional LASIKConventional LASIK

2.2. Astigmatic KeratotomyAstigmatic Keratotomy

3.3. Photorefractive KeratectomyPhotorefractive Keratectomy

4.4. PAI LASIKPAI LASIK

5.5. LASEKLASEK

6.6. OrthokeratologyOrthokeratology

7.7. Phakic Intraocular Lens(PIOL)Phakic Intraocular Lens(PIOL)

Physiological astigmatismPhysiological astigmatism

Almost all have minor degree of Almost all have minor degree of astigmatism {physiological }astigmatism {physiological }

Diameter of cornea in vertical axis is Diameter of cornea in vertical axis is 11.5mm and in horizontal meridian is 11.5mm and in horizontal meridian is 12mm.12mm.

This means horizontal meridian is This means horizontal meridian is flatter than vertical.flatter than vertical.

Because diameter is inversely Because diameter is inversely proportional to curvature. proportional to curvature.

Occur as lid press on anterior corneal Occur as lid press on anterior corneal

surface.surface.Make vertical meridian steeperMake vertical meridian steeperOnly small astigmatic errorOnly small astigmatic errorUsually 0.12DUsually 0.12DNO TREATMENT REQUIRED,NO TREATMENT REQUIRED,

life is an echo ,all comes back ,the life is an echo ,all comes back ,the good ,the bad, the false and the good ,the bad, the false and the truetrue, ,

so give the world the best u have and so give the world the best u have and the best will come back to uthe best will come back to u. .

For Further Queries Contact :For Further Queries Contact :

Ms. Priyanka SinghMs. Priyanka Singh

Head – Optometry ServiceHead – Optometry Service

Email – Email – [email protected]@venueyeinstitute.org