Free previewYou're reading the free part of this topic. The rest is included with Clinical.See what's included
Astigmatism and cylinders
Anatomy & Optics
Key Points
- •Astigmatism produces two focal lines (Sturm's conoid) instead of a single point; the circle of least confusion lies midway between them
- •WTR astigmatism (steep vertical, minus cyl axis at 180°) is common in young patients; ATR (steep horizontal, minus cyl axis at 90°) increases with ageing
- •The Jackson cross cylinder refines both axis (handle at axis, flip and compare) and power (axis of JCC at cylinder axis, flip and compare) during subjective refraction
- •Irregular astigmatism (keratoconus, scarring) is NOT fully correctable with cylinders - requires RGP/scleral contact lenses or topography-guided ablation
- •Spherical equivalent = sphere + cylinder/2 - places the circle of least confusion on the retina
Free preview ends here
Keep reading Astigmatism and cylinders
17 more sections are included with the Clinical plan.
- Definition
- Epidemiology
- Aetiology and causes
- Pathogenesis
- Classification
- Risk factors and associations