Which condition occurs when parallel light rays form two images in different meridians?

Which condition occurs when parallel light rays form two images in different meridians?

• A. Amblyopia
• B. Presbyopia
• C. Myopia
• D. Astigmatism

Answer: (D)

The main idea is how refractive errors can create different focal points for light depending on direction. In astigmatism, the cornea (or lens) has uneven curvature in different meridians, so light parallel to the eye doesn’t converge to a single point on the retina. Instead, there are two principal focal points along perpendicular meridians, so parallel rays form two images in different meridians, leading to blurred or distorted vision. This is why astigmatism produces ideas of two images or distorted lines, unlike myopia or hyperopia where there’s a single focal point in front of or behind the retina, or presbyopia where accommodation is lost. Corrective cylindrical lenses address the different powers in the two meridians to bring both focal points onto the retina.

The main idea is how refractive errors can create different focal points for light depending on direction. In astigmatism, the cornea (or lens) has uneven curvature in different meridians, so light parallel to the eye doesn’t converge to a single point on the retina. Instead, there are two principal focal points along perpendicular meridians, so parallel rays form two images in different meridians, leading to blurred or distorted vision. This is why astigmatism produces ideas of two images or distorted lines, unlike myopia or hyperopia where there’s a single focal point in front of or behind the retina, or presbyopia where accommodation is lost. Corrective cylindrical lenses address the different powers in the two meridians to bring both focal points onto the retina.