NDA (II) 2016 General Ability Test · Question 77 of 150

Correct — B, presbyopia. Reading a newspaper is a near-vision task, and presbyopia is the one defect in this list that attacks near vision alone and does so in almost everybody. With age the crystalline lens stiffens, so the ciliary muscle can no longer squeeze it into the fat, short-focus shape that near work demands. The eye's power of accommodation shrinks, the near point drifts outwards past comfortable reading distance, and print at arm's length turns blurred while distant objects may still be perfectly sharp. A convex reading lens supplies the extra converging power the lens can no longer produce, which is exactly the pair of glasses the man in the stem cannot do without.

• (a)myopia — Myopia is short sight — the eyeball is too long or the eye too powerful, so parallel rays from a distant object come to a focus in front of the retina. A myope's trouble is with the blackboard and the road sign, not the newspaper; uncorrected myopes typically read near print more comfortably than anyone else. It is corrected with a concave lens, the opposite of what reading glasses provide.
• (c)astigmatism — In astigmatism the cornea, or sometimes the lens, is not curved equally in all directions, so lines running one way focus at a different distance from lines running at right angles to them. The blur is present at every distance, near and far alike, and the correction is a cylindrical lens. Nothing about astigmatism singles out reading, so it does not fit a complaint that is specifically about near print.
• (d)hypermetropia — The tempting near-miss, because long sight does make near work hard and is also corrected with a convex lens. The separation is by cause and by age. Hypermetropia is a structural mismatch — the eyeball is too short for the eye's power — and it is usually there from childhood, whereas presbyopia is the ageing of the lens itself and arrives in nearly every adult after about forty. A young hypermetrope can often clear the newspaper by accommodating hard; it is when that accommodating reserve dies away that glasses become compulsory, and that stage is presbyopia. The examiner's phrase 'most probably' is doing the whole job here.

Accommodation is the eye's ability to change the focal length of its crystalline lens so that objects at different distances all land sharply on the retina. The closest point the eye can still focus clearly is the near point, about 25 cm in a healthy young adult. Presbyopia is the age-related loss of this ability: protein changes make the lens rigid, the ciliary muscle can no longer deform it, and the near point retreats. It is a normal part of ageing rather than a disease, which is why almost everyone needs reading glasses eventually.

The item is really asking you to separate two defects that share a remedy. Both hypermetropia and presbyopia blur near vision and both are corrected with a converging lens, so the lens cannot tell them apart — the cause and the age can. Hypermetropia is about the shape of the eyeball and is usually lifelong; presbyopia is about the stiffness of the lens and is age-driven. Because a middle-aged adult reaching for glasses to read a newspaper is the single commonest eye complaint in the world, 'most probably' points to presbyopia. A useful cross-check is that a presbyope's distance vision is often untouched, while a significantly hypermetropic eye is under-powered for every distance.

• The near point of a normal young adult eye is about 25 cm; in presbyopia it moves steadily further away, which is why the newspaper gets held at arm's length.
• Presbyopia is usually noticed after about the age of 40 and keeps worsening until roughly 65, when the lens has lost nearly all its flexibility.
• The standard corrections are a concave lens for myopia, a convex lens for hypermetropia and presbyopia, and a cylindrical lens for astigmatism; a presbyope who is also short-sighted needs a bifocal.
• Presbyopia arises from stiffening of the crystalline lens, not from any change in the length or shape of the eyeball.

• Assuming that because hypermetropia and presbyopia both use a convex lens they are the same defect — the cause and the age of onset differ.
• Thinking a short-sighted person struggles to read; uncorrected myopes usually read near print comfortably.

NDA asks eye defects either as a one-line symptom-to-defect item like this one or as a defect-to-remedy matching set, so learn the four defects together with their corrective lenses in one table.

• practice — not a real PYQ

  The defect of vision in which the near point of the eye recedes with advancing age is

  • (a)myopia
  • (b)astigmatism
  • (c)presbyopia
  • (d)colour blindness

  Answer(c) presbyopia — the crystalline lens loses elasticity with age, so the eye can no longer accommodate for close objects.

• practice — not a real PYQ

  A cylindrical lens is prescribed to correct which one of the following defects of vision?

  • (a)Myopia
  • (b)Hypermetropia
  • (c)Presbyopia
  • (d)Astigmatism

  Answer(d) Astigmatism — the cornea is unequally curved in different directions, so a lens with different powers along two axes is needed.