Class 10 Myopia vs Hypermetropia: Lenses and Correction

Compare the two school-level models

Swipe across the table to see all columns.

Read the labelled model

Why the corrective lens works

In myopia, a diverging lens spreads the incoming rays before they enter the eye. The eye then focuses the corrected bundle on the retina. In hypermetropia, a converging lens helps converge rays from a nearby object so the final focus can fall on the retina.

Accommodation is the eye’s adjustment of lens shape to focus at different object distances. It does not mean moving the retina backwards and forwards. Presbyopia is an age-related reduction in accommodation and should not be treated as another name for myopia.

Connect a lens name to its power

Lens power in dioptres is P = 1/f when f is in metres. A corrective lens with focal length −0.50 m has power −2 D. The negative sign identifies a diverging lens in air, consistent with the school model for myopia.

If focal length is given as −50 cm, convert it to −0.50 m before taking the reciprocal. Writing −1/50 D mixes the centimetre value with a formula requiring metres. These examples explain textbook optics, not an individual spectacle prescription.

Write an explanation that connects cause and correction

A useful answer has three connected parts: name the visual difficulty, locate the uncorrected image relative to the retina, and explain how the chosen lens changes ray convergence. A table helps revise the contrast, but practise writing the causal sentence too.

For a ray diagram, mark the retina clearly and label whether the drawing shows the defect or its correction. Do not label an image before the retina while drawing the rays meeting behind it.

Choose what to study next

Sources and scope

This is a focused learning resource, not a complete chapter or a prediction of board questions. Use your current syllabus and the paper-specific marking scheme for assessment requirements.