Download Self-tests in Optic and Refraction by Chua Chung Nen ,Mahadhir Alhady Sulaiman , Tan Aik Kah PDF

By Chua Chung Nen ,Mahadhir Alhady Sulaiman , Tan Aik Kah ,Ngo Chek Tung

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If he is emmetropic, the 4D of accommodation is adequate for an object at 25cm. If he is myopic, the amount of accommodation required will be less but if the he is hypermetropic, the amount of accommodation needed will be greater than 4D and plus lens will be needed. 5. T The Franklin design is a split bifocals in which a distance lens is mounted on a near lens. The cemented designs involves attaching a supplementary lens to the surface of a distance lens of the same refractive power. Fused bifocals is made by 59 heat-fusing a near portion made of flint glass into a depression on a crown glass with a lower refractive index.

Bifocals are used for children with convergence excess esotropia but not in high myopes. The problem of prismatic jump is related to the power of the lenses as well as the distance between the distance of the interface from its optical centre. 6. F Image jump can be reduced by moving the optical centres towards the junction of the two portions as in the executive glasses. Alternatively, a base up prism can be incorporated into the reading section. Pantoscopic tilt is used to reduce astigmatic aberration.

T Presbyopia is multifactorial and is believed to result from poor ciliary muscle contraction with age and age-related sclerosis and loss of elasticity of the lens fibres and the lens capsule. 3. T A child has about 14D of accommodation which decreases with age. In order to focus an object at a distance of 25cm, an emmetropic eye needs to use 4D of accommodation. 00D, only 1D is needed. 00D, 6D of accommodation is required (the accommodation is the sum of the patient's refractive state + 4D). For comfortable near vision, one-third of accommodation should be kept in reserve.

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