Astigmatism 1122020 1 Definition Astigmatism is defined as

Astigmatism 11/2/2020 1

Definition Astigmatism is defined as that dioptric condition of the eye in which a “point” focus is not formed on the retina 11/2/2020 2

Aetiology l Usually the cornea; rarely lens, IOL, etc. l Error in curvature in cornea or lens l Error in centering of lens or IOL l Error in refractive index of lens 11/2/2020 3

Physiological Astigmatism l Vertical corneal meridian is more curved than the horizontal l Seen in children and young adults l Gradually decreases with age l Constant pressure of the upper lid over the globe l In old age-Inverse astigmatism. Horizontal meridian is more curved than the vertical 11/2/2020 4

Types of Astigmatism 11/2/2020 5

Types of Astigmatism Irregular Astigmatism Mixed Simple Astigmatism Myopic 11/2/2020 Compound Astigmatism Hypermetropic 6

Classification of Astigmatism Regular Astigmatism Oblique Astigmatism With the rule Against the rule 11/2/2020 Irregular Astigmatism Bi-Oblique Astigmatism 7

Classification of Astigmatism Irregular Astigmatism Bi-Oblique Astigmatism Regular Astigmatism Mixed Astigmatism Compound Astigmatism Simple Astigmatism Regular Astigmatism With the rule 11/2/2020 Against the rule 8

The corneal meridians 11/2/2020 9

Variations in the corneal meridians +1 D +2 D +1 D 11/2/2020 10

Types of Astigmatism 11/2/2020 11

Types of Astigmatism 11/2/2020 12

Types of regular astigmatism 11/2/2020 13

Simple Astigmatism 11/2/2020 14

Compound Astigmatism 11/2/2020 15

Mixed and Irregular Astigmatism 11/2/2020 16

Symptoms l Diminution of vision l Distortion of images l Asthenopia due to accommodative effort l Headache or brow ache 11/2/2020 17

Optical treatment l Spectacle – Full correction usually – Under-correction if intolerable symptoms l Contact lenses – In small errors- spherical equivalent – In large errors- toric / rigid contact lens 11/2/2020 18

Surgical treatment l Astigmatic keratectomy l Laser refractive surgery 11/2/2020 19

Irregular astigmatism l Treatment is unsatisfactory l Keratoplasty may be required in keratoconus 11/2/2020 20

EXAMPLES l Simple Myopic Astigmatism with the rule 11/2/2020 Sph Cyl Axis - -3. 0 D 180 21

l Simple Myopic Astigmatism against the rule 11/2/2020 Sph Cyl Axis - -2. 0 D 90 22

l Simple Hypermetropic Astigmatism with the rule 11/2/2020 Sph Cyl Axis - +2. 0 D 90 23

l Simple Hypermetropic Astigmatism against the rule 11/2/2020 Sph Cyl Axis - +1. 5 D 180 24

l Compound Myopic Astigmatism with the rule 11/2/2020 Sph Cyl Axis -2. 0 D -1. 0 D 180 25

l Compound Hypermetropic astigmatism Astigmatism with the rule 11/2/2020 Sph Cyl Axis +2. 0 D +1. 0 D 180 26

l Mixed astigmatism 11/2/2020 Sph Cyl Axis +1. 0 D -3. 0 D 180 27