Topic 1: Frame Selection

Question 1

what are the benefits of a well fitting frame

Answer 1

(1) good wearing comfort for whole day
(2) consistent vertex distance for effective vision correction (if temple too long, too little grip, spectacles slip downwards, vertex dist increase) - metal temples usually allow trimming
(3) lens optical axis aligned to the eyes’ centre of rotation and visual axis. hence minimum aberrations and prismatic effects

Question 2

state the sequence for checking fit of spectacles

Answer 2

width, nose, temple

Question 3

define width of face

Answer 3

the temple leaves the frame front, goes back straight and only touches the face where it meets the ear

Question 4

explain checking width

Answer 4

frame pd = px pd is acceptable

frame pd > px pd (too big frame), px pd > frame pd (too small frame) are not acceptable

Question 5

explain checking nose

Answer 5

look closely and from a few angles

schnoz = wide bridge

button = narrow bridge

flat nose = nose pads

plastic frames must fit px shape to shape

looks out for maximum contact

Question 6

explain checking temple length

Answer 6

should rest 2/3 behind top of ear

Question 7

state the 3 positions of wear

Answer 7

vertex distance, wrap angle/face form, pantascopic tilt

Question 8

explain vertex distance

Answer 8

distance between lens and cornea apex

12-15mm to math VD from trial frame

check for small VD (eyelashes touch lens) and excess VD (esp Rx > 5D as lens effective power will change)

metal frames with adjustable nose pads good for flat noses when maintaining VD

Question 9

explain wrap angle/face form

Answer 9

ideal: positive face form/ frame pd>px pd - gentle curve around face (6-8 degrees), allows for lens axes to pass through centre of rotation of the eyes to minimise aberrations

Question 10

explain pantoscopic tilt

Answer 10

angle between the lens place and vertical plane. influenced by the position of the ear in relation to the bridge (higher ears, more tilt, bottom lens towards face

othoscopic/no tilt: lens plane perpendicular to the floor

retroscopic tilt: bottom of lens is further away from face (not ideal as wearer will read through the gap and there will be unwanted lens aberration as lens axis does not match with visual axis)

Question 11

state rule of thumb when choosing frames for certain face shapes

Answer 11

oval faces are ‘ideal’ - suit any

avoid repeating shape you see (round face, don’t suggest round frame)