PRESBYOPIA

Presented by

N.Pitchaimeena

Definition

Inability to read the books at the normal reading distance of 33cm.

The near point recedes beyond the arm’s length.

Causes

Decrease of accommodative power

Nuclear sclerosis- Lens become harder

Variation of accommodation with age

Amplitude of accommodation

Age

Early age 36years 45years 60years

14D 7D 4D 1D

Near point 7cm 14cm 25cm 1meter

Contd.

The lens in accommodation

Some important points

Average distance for near work is 28-30cm.When the amplitude of accommodation is less then 3.0Ds Presbyopia is said to start.Comfort demands that about 1/3 of accommodation to be kept in reserveIn emmetropic presbyopia occurs at 40 – 45 years of age in foreign countries 38 – 40 in India.Accommodation must be supplemented by convex lenses

Contd.

In hypermetropia presbyopia comes earlier , myopia later.Myopia –4.0Ds presbyopia will not occur.A person who has habit of reading with his book on his knees complaints of discomfort later than one who is used to reading more closely.Ciliary muscles fails – in debility & disease

Symptoms

Trouble is in the evening, when light is dim, and pupils are dilated.Likes to read in brilliant illumination when the pupils will be forced to contract.Visual failure Eye strain The ciliary muscle working near its limit becomes fatigued and accommodation effect strained in excess of the convergence-giving rise to distress.HeadacheEyes feels tired & ache.

Treatment

Provide the patient with the appropriated convex lens , so that his accommodation is reinforced and the near point is brought within the useful working distance.Know the working distance of the patient for proper addition.RefractionDetermine the amplitude of accommodation1/3 of accommodation is kept in reserve Supplement this by lens

Scientific calculation of presbyopic correction

Example Emmetropic working distance :– 25cmRequired amplitude of accommodation :– 4D(100/25)Near point receded at 50cm (WD)His accommodation :– 100/50 = 2DKeep 1/3 reserve for comfortAvailable accommodation :– 2/3 of the amplitude = 1.3DRequired lens power :– (4 –1.3D) = 2.7Ds

Points to remember

Presbyopic spectacle should never be prescribed mechanically based on ageLenses must be serviceable and comfortable, not necessarily the clearest.Vision for the particular work for which their spectacle is intended must be kept in the mind.Start with an addition of +0.75D.Better to under correct than over correctLenses that bring the near point closer than 28cm is rarely tolerated.

Contd.

Demand for higher correction , than convergence should be aided with prism base in.

Patient with early cataract can read with +3.5D or +4.0D addition

Usual discomfort for presbyopic optical correction is due to over correction