Astigmatism Lab

What causes blurred or distorted vision in astigmatism?

Uneven curvature of the cornea or lens, leading to distortion along a specific direction.

What must glasses for astigmatism correct?

Both the angle (direction) and the strength (lens power) of distortion.

What does refractive power refer to?

How much a lens bends light.

What is the unit of refractive power?

Diopter.

What do positive diopters indicate?

Convex lenses that bend light more; used to correct hyperopia (farsightedness).

What do negative diopters indicate?

Concave lenses that bend light less; used to correct myopia (nearsightedness).

What does lens power determine in astigmatism correction?

How much of the blurring is corrected.

What does lens angle determine in astigmatism correction?

Which direction the blurring is corrected.

What happens if the correct power is used at the wrong angle?

Blurring can become worse.

What effect does a zero-power lens have, regardless of angle?

No effect—it won't correct the blurring.

Why is accurate measurement of both angle and power important?

To effectively correct the patient's distorted vision without worsening it.

What tool is used to determine astigmatism angle and strength?

The astigmatism chart.

On the astigmatism chart, what do the sharpest lines represent?

The angle of astigmatism.

What direction is 0 degrees on the astigmatism chart?

The 3 o’clock direction (horizontal).

What direction is 90 degrees on the astigmatism chart?

The 12 o’clock direction (vertical).

If the sharpest lines appear at 11 o'clock, what angle does that correspond to?

120 degrees.

How do you determine the power of the corrective lens for astigmatism?

Adjust lens power until all lines in the chart appear equally sharp.