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Weight & Thickness of Lenses

Weight & Thickness of Lenses. Identify the plus and minus lenses Plus lenses are thickest in the centre and get thinner towards the edge Minus lenses are thin in the centre and get thicker towards the edge. PLUS lenses . MINUS lenses . Frames – fitting. HCL.

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Weight & Thickness of Lenses

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  1. Weight & Thickness of Lenses Identify the plus and minus lenses Plus lenses are thickest in the centre and get thinner towards the edge Minus lenses are thin in the centre and get thicker towards the edge PLUS lenses MINUS lenses

  2. Frames – fitting HCL • Properties of a well fitting frame: • Appears straight on face • Well fitting on the nose • A large enough size so that person does not aware of edges of frame • Eyes fairly well centred • – horizontally • – vertically (usual for eyes to be a little higher in frame) • Lenses frame not too far away from the eyes • well fitting behind ears

  3. Frames – fitting HCL Frame types Metal OR Plastic Full frame Rimless frame half-rimless frame

  4. Frame too small 2 3 1 Too narrow for face, bending back at hinge to get to ears Eye size of frame not big enough for this person, sitting quite high Frame sitting slightly tilted on face Coming up off the ear on second photo

  5. Frame too big 3 2 1 Pupils very high in this frame Eye size of frame too big/deep for this person Again, frame slightly tilted on face Actually quite good width overall

  6. Well fitting Frame 1 3 2 Frame good width and shape on bridge of nose Eye size of frame quite deep, but person has varifocal lenses, and frame has enough height above pupils Frame level

  7. Well fitting Frame 2 3 1 Frame good width on face Frame eye size has sufficient depth & is good size over bridge of nose Frame level – but facial asymmetry - Right eye higher than left Good fit over ear & appropriate tilt of frame on second photo 4

  8. Spectacle Prescriptions Spherical Cylindrical • Analysing a spectacle prescription • Is it a myopic, hyperopic and/or astigmatic prescription? • Is it a moderate/high prescription? R +2.25 / -2.00 * 180 L +1.75 / -1.50 * 170

  9. 4 Spectacle Prescriptions • Lens Materials • Ideally we want a lens to be light, thin and clear with little reflectance and that they are robust • Nowadays, lenses are mostly made from Plastic material. This is safer and lighter than glass • Basic lens material is called CR39 • Lenses can be made thinner and lighter if they are made out of denser materials. These are called ‘high-index’ materials. There are a variety of types. They have slightly different properties. • If prescription is moderate/high, advantageous that lenses are made from high-index material. Lenses will be thinner and lighter.

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