Eye Defects and the Endocrine System [H]

This lesson covers common eye defects and how they are corrected, then introduces the endocrine (hormonal) system. Understanding eye defects is Higher Tier content. The endocrine system is required for all tiers and is the foundation for lessons on blood glucose regulation and reproductive hormones.

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Common Eye Defects

Two common eye defects affect the ability to focus light correctly onto the retina: myopia (short-sightedness) and hyperopia (long-sightedness).

Myopia (Short-sightedness)

A person with myopia can see near objects clearly but distant objects appear blurred.

Cause: The eyeball is too long, or the lens is too thick (too curved). Light from distant objects is focused in front of the retina instead of on it.

Correction:

• Concave (diverging) lens — placed in glasses or contact lenses to spread out light rays before they enter the eye, so they focus on the retina.
• Laser eye surgery — reshapes the cornea to change its refractive power.
• Replacement lens surgery — an artificial lens replaces the natural one.

Hyperopia (Long-sightedness)

A person with hyperopia can see distant objects clearly but near objects appear blurred.