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


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)

  • Older patients:
  • Patients older than ~50 years will have a low amplitude of accommodation & will only be able to read N5 print at the end of the rule
  • In all patients 50 & older: in addition to distance Rx place a pair of +2.00DS in the trial frame before measuring the amplitude. Deduct 2.00 from the value found on RAF rule (e.g. reads as 5.50D on RAF rule therefore amplitude is 3.50D)
  • Measuring Accommodation with RAF rule:
  • Use push up method where you push target up, so initially it’s clear then it becomes blurred
  • Amplitude for distance of accommodation is the distance at which the target just becomes clear by patient before it blurs
  • Consider influencing factors:
  • Age & refractive error
  • Motivation
  • Lighting
  • Look for:
  • Age correlation
  • Similarity between the eyes
  • Difficulties when binocular
  • If the amplitudes are:
  • Unequal: (not common to even have a dioptre of distance between the two eyes) check the balance of your refraction & the VA’s. If definitely unequal by >~1.00D investigate, refer?
  • Binocular not greater than monocular: check convergence
  • Less than 4.50D: becoming presbyopic, will need a near addition
  • (if amplitude of accommodation is not correlating with age then check distance prescription/history/medications etc.)

Determining near addition

  • The Near Add is the amount of plus sphere a patient needs to supplement his declining accommodation so that they can read small print at the desired working distance

(this will of course blur their distance vision – it will be dispensed as bifocals, varifocals or as a separate pair of reading spectacles)

  • Formula to work out Near Add: (1/WD) – (2/3)AA
  • The near Rx is usually a spherical positive addition to the distance Rx which we have already determined (cyl & axis not changed)
  • Estimating the Near Addition
  • Define the requirement

Typically a patient wants to read small print e.g. a newspaper at ~33cm therefore usual demand is 3.00D of accommodation

Check the demand on the particular patient by measuring the distance the patient wants to hold the newspaper while reading (e.g. measures as 30cm – ~3.25D)

  • How much focussing power at near can the patient supply?

If it was a young patient with accommodation of 10.00D R&L, 3.25D is only a small proportion of 10.00D, therefore no need for a reading addition

If an older patient with 3.50D R&L, 3.25D is almost all the amplitude; it’s likely to find using this much accommodation over a sustained period – uncomfortable & blurry

  • Rule of thumb:

Patients can use continuously 2/3 of their amplitudes of accommodation without blur or discomfort

Having to use more than 2/3 for a sustained period gives rise to blur & discomfort

At 45 y/o the typical amplitude is 4.50D, 2/3 of 4.50D = 3.00D, just fulfils typical near demand of 3.00D. Therefore any less than 4.50D amplitude is presbyopic.

(However, need for presbyopic correction depends on patients’ working distance which is not always 33cm!

  • Checking the addition
  • Put the estimated reading addition in the trial frame
  • Ask patient to read N5 at desired reading distance
  • Move the print closer to the patient & note the distance where it blurs. Move the print further away, note blurring distance (we want to give them as large a range as possible, either side of near add)
  • If the distances are equal the addition is correct
  • If blurs immediately on coming closer increase the addition until distances are equal (~+0.50DS)
  • If blurs immediately on moving away decrease the addition (~0.50DS)

(If you reduce plus, range will increase at back, if you add plus range increases at front)

  • Determining Near Addition:
  • Use near duochrome (always on green – want a little bit of accommodation to be active)
  • Check each eye separately
  • Do not over plus
  • Make sure working range is appropriate
  • Consider different Rx for different distances (e.g. reading & computer)
  • Near Tests:
    • The subsequent tests, Maddox Wing etc are done with the near addition in place.

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