Astigmatism is a refractive error where the refraction varies in different meridians, causing light rays to focus as lines rather than points on the retina. There are two main types: regular astigmatism where refractive power changes uniformly between meridians, and irregular astigmatism where changes are irregular. Regular astigmatism is classified based on the axis of the two principal meridians as with-the-rule, against-the-rule, or oblique. Symptoms include blurred vision, eyestrain, and tilting of the head, and it is diagnosed through retinoscopy, keratometry, and astigmatic tests. Treatment involves prescribing cylindrical lenses through glasses or contacts.

1. MANISH CHAUDHARY
NIOR
*

2. *Astigmatism is a type of refractive error wherein the
refraction varies in different meridian .
*The rays of light entering can not converge to a point
focus but form focal lines.

3. *
*There are mainly two types of astigmatism i.e
*REGULAR ASTIGMATISM
*IRREGULAR ASTIGMATISM
*REGULAR ASTIGMATISM: the astigmatism is
regular when the refractive power changes
uniformly from one meridian to another
meridian .

4. *Family history
*Advancing age
*Corneal scarring
*Corneal thinning
*Diabetes
*Pre-existing RE
*Severe allergies resulting in constant rubbing
*Preterm birth

5. *Corneal Astigmatism: (results from abnormalities of curvature of
cornea)
*Lenticular Astigmatism: ( curvature ,positional,index)
*Retinal astigmatism(due to oblique placement of macula )

6. *
*Depending upon the axis and angle between the two principal
meridian, regular astigmatism can be classified into the following :
*1.with the rule astigmatism :two principal meridian are placed at
right angles to each other ,but the vertical meridian is more curved
than the horizontal meridian . So the correction required is concave
Cyl at 180 or convex Cyl at 90.
*Against the rule astigmatism : condition in which the horizontal
meridian is more curved than the vertical meridian .
so correction required is convex CYL at 180 0r concave CYL at 90.

7. *Oblique Astigmatism: where the two principal meridian re not the
horizontal or vertical though these are at right angled to one
another.(eg.45 and 135)
*BI-Oblique astigmatism : two principal meridian are not right angle
to each other .(eg.one may be at 30 and other at 100).

8. *
*As already mentioned earlier that in regular astigmatism ,the
parallel rays of light are not focus on a point but form two focal
lines.
*The configurations of rays refracted through a toric surface is called
strum’s conoid and the distance between the two focal interval is
the measure of a degree of astigmatism .

9. *
*Depending upon the position of the two focal lines in relation to
retina ,the regular astigmatism is further classified into three types ;
*1.simple astigmatism : wherein the rays are focused on the retina
in one meridian and either in front (simple myopic astigmatism )or
behind (simple hypermetropic astigmatism ).
*Compound astigmatism : where the rays of light in both meridian
are focused either in front or behind the retina .thus in 1 meridain
eye is myopic and and in other hypermetropic .
*Mixed astigmatism :where the light rays in one meridian are focuded
in front and in other meridian behind the retina .

10. *
*Blurring of vision : in patients with low astigmatism (<1.0D),there
occurs transient blurring of vision.
*Asthenopic symptoms : these include tiredness of eyes, headache,
dizziness , irratability.
*Tilting of head : some patient with high oblique astigmatism may
hold the head tilted to one side so as to reduce image distortion.
*Squinting of eye ,frequently seen in patients with high astigmatism.
*Reading material may be hold close to eyes
*Burning and itching sensation may be experienced

11. *
*Retinoscopy revels different power in two different axes
*Keratometry and computerized corneal topography reveal
different corneal curvature in two different meridian in corneal
astigmatism .
*Astigmatic fan test:
*Jackson cross cylinder test is very useful in confirming the power
and axis of cylindrical lenses.

12. *
*Optical treatment :comprises prescribing the appropriate
cylindrical lenses
*Cyl lenses may be prescribed in form of spectacles and RGP CL
(may correct upto 2-3 D)

13. *It is characterized by an irregular change of refractive power in
different meridian.
*Aetiological type :
*1.corneal irregualar astigmatism is found in patients with extensive
corneal scars or keratoconus .
*2.lenticular irregular astigmatism is seen due to variable refractive
index in different parts of the crystalline lens and may occur rarely
during maturation of cataract .
*3.retinal astigmatism : is seen due to the distortions of the macular
area due to scarring or tumours of retina and the choroid pushing the
macular area.

14. *
*Symptoms :
*Defective vision
*Distortion of objects and
*Polyopia
*Signs:
*Retinoscopy revels irregular pupilary reflex.
*Slit-lamp examination may revel corneal irregularity of
keratoconus .
*Placido disc test reveals distorted circles
*Photography and computerized corneal topography gives
irregular corneal curvature.

15. *
*1.optical treatment of irregular astigmatism consist of prescribing
contact lens which replaces the anterior surface of the cornea for
refraction.
*2.phototherapeutic keratectomy performed with excimer laser
may be helpful in patients with superficial corneal scar
*3.surgical treatment is indicated in extensive corneal scarring
(when vision does not improve with cl ) and consists of
penetrating keratoplasty).

16. *
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