RGP Lenses

Question 1

3 fundamental features of RGP

Answer 1

1. Centre of lens should clear central cornea
2. There should be mid-peripheral contact point along the horizontal meridian - the lens should land on the peripheral cornea at 3 and 9 o’clock - MOST IMPORTANT
3. The lens should maintain unobstructed movement along the vertical meridian

Question 2

Choice of RGP trial lens

Answer 2

<0.50DC - 0.05mm steeper than flattest K
0.50-1.00DC - 0.05-0.10mm steeper that flattest K
1.00-2.00DC - 1/3 difference steeper than flattest K
>2.00DC - Toroidal
ATR requires cyl sooner to assist centration

Question 3

RGP Total Diameter

Answer 3

Typically 9.8mm (Range between 8.50-10.50mm)
Smaller than HVID by 2mm
The larger the lens, the more stable it will be

Question 4

RGP BOZD

Answer 4

1mm larger than pupil in average illumination - ideally to encompass the whole pupil in dim illumination