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 age36years45years60years 14D7D4D1D Near point7cm14cm25cm1meter

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 reserve In 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. Headache Eyes 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. Refraction Determine the amplitude of accommodation 1/3 of accommodation is kept in reserve Supplement this by lens

Scientific calculation of presbyopic correction Example Emmetropic working distance :– 25cm Required amplitude of accommodation :– 4D(100/25) Near point receded at 50cm (WD) His accommodation :– 100/50 = 2D Keep 1/3 reserve for comfort Available accommodation :– 2/3 of the amplitude = 1.3D Required lens power :– (4 –1.3D) = 2.7Ds

Points to remember Presbyopic spectacle should never be prescribed mechanically based on age Lenses 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 correct Lenses 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