Astigmatism.pptx optometry. students....
- 1. ASTIGMATISM By- Mushahid Raza B.Optom Rama university, kanpur
- 2. Definition Astigmatism by definition is a condition where the parallel beam of light rays incident on the cornea after retraction are not focused to from a point image near or on the retina. Astigmatism is type of refractive error wherein the refraction varries in different meridian of the eye. The rays of light entering the eye can’t converge to a point focus but From focal lines.
- 3. Etiology • The refractive power is not uniform in all meridians of both lens or cornea. • The principal meridians are meridians of greatest and least refracting power. • Corneal Astigmatism – it’s results of abnormalities of curvature of cornea. • Lenticular Astigmatism – curvatural, positinal, Index astigmatism • Retinal Astigmatism - due to oblique placement of macula may also be seen occasionally.
- 4. Classification Classification of Astigmatism 1- Regular Astigmatism 2- Irregular Astigmatism Types of Regular Astigmatism – Depending upon the axis and the angle between the two meridians . Regular astigmatism can be classified into following types -
- 5. 1- With- the- rule astigmatism 2- Against-the-rule astigmatism 1) - With-the-rule astigmatism (WTR) – • Vertical meridians of cornea is more curved. • Myopic power is more in vertical meridian. • Eg:- -3. 0D cyl ×180° • Correction of this astigmatism will require the concave cylinder at 180° +- 20° , or convex cylindrical lens at 90° +- 20° .
- 6. Against-the-rule astigmatism (ATR) • Horizontal meridian of cornea is more curved. • Myopic power is more in horizontal meridian. • Eg:- -3. 0D cyl × 90° • Correction of this astigmatism will require the convex cylindrical lens at 180° +- 20° , or concave cylindrical lens at 90° +-20° axis.
- 7. Based on orientation of meridian 1> Oblique astigmatism 2> Bioblique astigmatism 1:- OBLIQUE ASTIGMATISM – • Axis is not on or near 90° or 180° • Range of axis lies in between 120°-150° and 60° - 30° . • Eg:- -3. 0 D cyl × 45° • 2:- BIOBLIQUE ASTIGMATISM – • The meridians are not perpendicular. • Eg:- -3. 0 D cyl × 90°/ -2. 0 D cyl × 110° .
- 8. Optics of regular astigmatism Sturm’s conoid -
- 9. Refractive types of regular astigmatism Depending upon the position of the two focal lines in relation to retina, Regular astigmatism is classified into following types – 1> Simple astigmatism – 1) Simple myopic astigmatism 2) Simple Hypermetropic astigmatism 2> Compound astigmatism 3> Mixed astigmatism
- 10. 1- simple myopic astigmatism – the rays are focused on the retina in one meridian and either in Front of the retina. 2- simple Hypermetropic astigmatism – the rays are focused on the retina in one meridian and either behind the retina. 2> Compound astigmatism – in this, the rays in both Meridians are focused either in front or behind the retina and the condition is labelled as compound myopic or c. Hypermetropic astigmatism. 3> Mixed astigmatism – in this, the rays are in one meridian are focused in front and in other meridian behind the retina.
- 12. Clinical feature Symptoms 1- Blurred vision and defective vision 2- Asthenopia ( tiredness of eyes relieved by closing the eyes) 3- Headache 4- Squinting 5- Ocular fatigue 6- Elongation of objects proportionate to the degree and type of astigmatism may be noticed in high astigmatism.
- 13. Signs 1- Half closure of lid. Like myopes the astigmatic patients may half shut the eye to achieve the greater clarity of Stenopaeic vision. 2- oval or tilted optic disc may be seen on ophthalmoloscopy in patients with high degree of astigmatism . 3-
- 14. Investigation / Clinical tests • Visual acuity test – near & distance • Retinoscopy • Keratometry • Autorefractimetry • Astigmatism fan test • Jackson cross cylinder test ( JCC)
- 15. Treatment 1- Optical treatment • Spectacles – cylindrical power and appropriate axis should be used for distance and near vision. • Contact lenses 2- Surgical correction of astigmatism
- 16. Irregular astigmatism Irregular change of refractive power in different Meridians. There are multiple meridians which admit no geometrical analysis. Etiological types – Curvatural irregular astigmatism Index irregular astigmatism
- 17. CLINICAL FEATURE Symptoms Defective vision Distortion of object Polyopia Signs Retinoscopy Slit lamp Photokeratoscopy
- 18. Treatment Optical treatment Phototherapeutic Keratectomy performed ( PTK) Surgical treatment