1. What are prisms Give the units for specifying power of a prism and explain the effect of prisms on the movement of the eye.

2. What is surfacing Explain the process of surfacing and describe the steps of lens surfacing.

3. Describe the various glass lens materials and plastic lens materials available in the market. Explain the manufacturing process of plastic lenses.

4. What is the importance of Interpupillary distance Explain the various methods of measuring IPD.

5. Describe in detail the methods of lens edging in various types of frames.

6. Describe the process of frame selection for various cosmetic reasons.

Write short notes on any six. Each carries 5 marks.

Trifocal lenses

Prentice Rule

Frame materials

Photochromatics

Temple-length

Advantages and disadvantages of High Index Lenses

Write down the spherical equivalent of the following prescriptions

-5.00/ +1·00 x 110°

4·0 cyl 70°

-2·00 cyl 150°

4.00/ 2·00 x 90°

-7·00/ 3.00 x 110°

Transpose the following in alternate forms:

-6.00/ 2·00 x 120°

-1·00 cyl 40°

3.00 -1·00 x 90°

6·00 cyl x 180°

2·00 x 170°