SHORT-SIGHT (MYOPIA) means being unable to see distant objects clearly — they appear blurred.
CAUSE:
The eyeball is too LONG (front to back), OR the lens is too curved (too powerful).
Light from distant objects is brought to a focus IN FRONT OF the retina — not on it.
The image on the retina is therefore blurred.
Close objects can still be seen clearly — the lens can round up enough to focus them.
CORRECTION:
CONCAVE (diverging) LENS — diverges the light rays before they enter the eye.
This moves the focal point backwards — onto the retina.
Concave lenses have a negative power value.
Can also be corrected by: laser eye surgery (reshaping the cornea to reduce its curvature).
PREVALENCE: short-sight has become more common globally — particularly in young people. Thought to be linked to increased close-up work (screens, reading) and less time outdoors.
Long-Sightedness (Hyperopia)
LONG-SIGHT (HYPEROPIA) means being unable to see near objects clearly — they appear blurred.
CAUSE:
The eyeball is too SHORT (front to back), OR the lens is too flat (not powerful enough).
Light from nearby objects would be brought to a focus BEHIND the retina — but the retina intercepts the rays before they converge.
The image on the retina is blurred.
Distant objects may be seen more clearly as they require less refraction.
CORRECTION:
CONVEX (converging) LENS — converges the light rays before they enter the eye.
This moves the focal point forward — onto the retina.
Convex lenses have a positive power value.
Can also be corrected by: laser eye surgery (reshaping the cornea to increase curvature).
AGE-RELATED LONG-SIGHT (PRESBYOPIA):
As people age, the lens becomes less flexible → cannot round up as much → difficulty focusing on near objects.
This is why many people need reading glasses after the age of 40–50.
Corrective Methods Compared
SPECTACLES (GLASSES):
Safest option — no surgery involved.
Easily updated as prescription changes.
Convex lenses for long-sight; concave lenses for short-sight.
CONTACT LENSES:
Sit directly on the cornea.
Invisible when worn — cosmetic advantage.
Risk of infection if not handled hygienically.
Same lens types as glasses (concave or convex).
LASER EYE SURGERY:
Uses a laser to reshape the CORNEA — permanently altering its curvature.
Short-sight: cornea flattened → less refraction → focal point moves back.
Long-sight: cornea made more curved → more refraction → focal point moves forward.
Permanent correction — no need for glasses or contacts afterwards.
Risks: dry eyes, glare, halos, rare complications. Only suitable for adults with stable prescription.
⚠️ Common Mistake
Short-sight is corrected by a CONCAVE lens (diverging). Long-sight is corrected by a CONVEX lens (converging). Students often get these the wrong way round. Memory tip: Short-sight = Concave = diverging (spreads light out, moves focal point back). Long-sight = convex = converging (brings light together, moves focal point forward).
📌 Key Note
Short-sight (myopia): eyeball too long, image in front of retina → correct with CONCAVE lens. Long-sight (hyperopia): eyeball too short, image behind retina → correct with CONVEX lens. Laser surgery reshapes cornea permanently.
🎯 Matching Activity — Short-sight or Long-sight?
Match each feature to short-sight or long-sight. — drag the symbols on the right to match the component names on the left.
Short-sight
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Long-sight
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Short-sight
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Long-sight
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Short-sight
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Long-sight
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Corrected with a convex (converging) lens
Corrected with a concave (diverging) lens
Image forms in front of the retina
Cannot see distant objects clearly — eyeball too long or lens too curved
Cannot see near objects clearly — eyeball too short or lens too flat
Image would form behind the retina
🎯 Test Yourself
Question 1 of 2
1. A student cannot see the board clearly but can read their textbook easily. What is the most likely condition and correction?
2. How does laser eye surgery correct short-sight?
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