Accommodation, Presbyopia & Near Additions

The eye can increase its power to focus on near objects

The ciliary muscle controls the tension on the zonule – this allows the ciliary muscle to contract, causing the zonule fibres to relax, causing the lens to thicken/bulge out & this increases the power of the eye

SEE GRAPHS ON LECTURE

With high minus lenses the eye accommodates a lot, creating an unsteady line on graph (VA becomes unsteady)

When refractive error is higher than the amplitude of accommodation (how much we’re able to accommodate) then VA deteriorates/is weak

The highest peak of graph (best VA) is the most plus/least minus that gives the best VA

If you give any more plus VA deteriorates

  • At birth, our amplitude of accommodation is ~20.00D, it reduces with age from the day we are born – this happens because the lens capsule in the eye loses its elasticity & the number of fibres increases over time.
  • This varies between people but we don’t notice it happening – only when amplitude goes below that needed for reading do we notice it reducing
  • Each individual probably has a linear reduction of amplitude (& hence reduction of being able to focus at near) with age (can lower to as far as 0.50D)
  • If you have 2.00D amplitude of accommodation, you can only see as close as 50cm (1/2 = 0.5m)
  • Presbyopia happens to everyone & is not related to patient’s refractive error (therefore near tests should be done on everyone) – presbyopes may require additional tests
  • Reading glasses, positive spheres make near objects clear (& distant objects blurred)
  • Pre-presbyopes are usually less than 45 y/o & have adequate amounts of accommodation for near vision
  • Presbyopes need near Rx, as their accommodation is no longer adequate for near vision. They are generally over 45 y/o but may depend on: race, occupation, environment (e.g. light levels – higher light levels of sunlight/UVradiation causes lens to go through aging process quicker i.e. in hot country), pupil size, medication etc.
  • Regardless of refractive error, when wearing the distance correction near objects are blurred
  • Presbyopes therefore need different correction for distance & near
  • ALWAYS consider near visual requirements for ALL PATIENTS
  • All tests so far have been at 6m
  • Now consider near vision – usually 33-40cm
  • Adjust trial frame for near PD
  • Adjust lighting levels to match patients’ usual setting (artificial light/bright light makes pupil smaller so acts as a pinhole to make vision clearer)
  • Tests for near vision:
  • Near acuities – monocularly & binocularly
  • Accommodation – monocular & binocular
  • Determination of near addition if presbyopic
  • Convergence
  • Near Acuities:
  • Important to determine & record near acuities & the distance at which it’s measured (ask patient to hold a book at their normal reading distance & measure distance from book to eye – this is after you’ve added the near addition for presbyopes/older patients)
  • Do this for each eye independently
  • If they have poor near acuity may need to determine near addition first – e.g. presbyopes
  • Measurement of the Amplitude of Accommodation (for everybody)
  • Distance correction in place
  • Occlude each eye in turn
  • Use the RAF rule:
  • Bring N5 print closer to the eye until it blurs
  • Move print away from eye until just clears
  • Read off the value (in dioptres)
  • Repeat for other eye
  • Repeat binocularly
  • Values should be:
  • Equal in the two eyes
  • Correct for the age
  • Binocular > monocular (~0.50D)

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