Frames and Vision

Question 1

Box System of Measurements

Answer 1

• 2 sets of number used
• horizontal lens size + bridge size = box centre
• bridge size is the distance between both lens frames

Question 2

Frame Markings

Answer 2

1) horizontal lens size x distance bet lenses (mm) eg 50x18
2) Total length of side (mm) eg 135
3) Manufacturer/design/suppliers name or trademark
4) Frame model
5) Frame colour

Question 3

Effective Lens diameter

Answer 3

Distance from centre of lens to widest part of lens multiplied by 2

Question 4

Field of View

Answer 4

=total area visible through the lens when the eye is in its primary position

• positive lens means FOV is less
• negative lens increases FOV

Question 5

Apparent FOV

Answer 5

Angle subtended by the empty frame aperture at the eyes centre of rotation

Question 6

Real FOV

Answer 6

FOV obtained when a spectacle lens is glazed into the frame

Question 7

FOV is influenced by:

Answer 7

• Frame and therefore lens shape
• vertex distance
• power of the lens (real FOV only)

Question 8

Near Vision Effectivity Error

Answer 8

-mainly effects people who wears positive lens
- back vertex power of lens - vergence which leaves the lens when light originates from a distant object
near vision - light not arriving from the lens at near also depends on thickness and form of lens
-vergence leaving the lens at near also depends on thickness and form of lens
- lenses with same back vertex power but of diff forms are not interchangeable
NVRE = diff bet the image vergence produced by a thick lens at near and the expected vergence from a thin lens

Question 9

Lens Mountings

Answer 9

can be:

• full rim
• rimless
• supra

Question 10

Lens edge

Answer 10

will be different depending on the frame mounting type, to allow the lens to remain securely in the frame:

• bevel
• supra
• flat
• mini bevel

Question 11

Frame Bridge

Answer 11

= the bridge forms the main connection bet the right and left rims. It may or may not have pads
- diff designs for plastic and metal frame s

Question 12

Frame Pads

Answer 12

=extensions or attachments to the bridge which form the bearing surface of the frame for the nose
-pads for a fixed pad bridge frame are moulded into the rim and are the same material as the frame itself

Question 13

Bridge types

Answer 13

Fixed pad bridge - plastic frames only, moulded pad shapes

Regular bridge - plastics frames only, no moulded pad shapes

Question 14

In Metal frames, pads are:

Answer 14

pads are on arms

• pads on arms can be screw in or push in
• made from silicone (flexible lightweight, soft) or vinyl (lightweight, rigid, cheaper)
• can be saddle/comfort/strap bridge with same material and attachment

Question 15

Sides

Answer 15

can be drop end, loop end, curl sides