5.1.3-RGP choose/order/fit

Question 1

How does total diameter of an RGP effect centre of gravity, stability and the fit?

Answer 1

A larger TD gives a more stable lens as the centre of gravity is further back, it reduces 3&9 o clock staining but there is more risk of limbus interaction

Question 2

Go through a routine assessment of RGP VA+FIT and what good, steep and flat is like

Answer 2

1. After 20min settling period (might be 5-15mins- depends on when reflex tearing stops)
2. Ask about lens comfort and vision in each eye, get general feedback from px. With a steep lens, px will report minimal lid sensation; with a flat lens comfort is poor with excessive tearing even after adaptation
3. VA and spherical overrefraction with binocular balancing- VA should be crisp and stable. If unstable or unacceptable then a cylindrical refraction (can use objective and subjective). For front surface torics do over refraction after checking lens stability because that has to be sorted first (consistent lens rotation= LARS/CAAS, inconsistent rotation=change stabilisation technique). A flat fit may give a + over-refraction and a steep fit a - over-refraction
4. Assess centration using white light and normal head postition- is it crossing the pupil zone (could use ret for this and check if the reflex is straight or if it is flaring), is it crossing the limbus, is it attaching to any lid, is it intra-palpebral or lid attachment fit. A good lens is covering the pupil, slight superior displacement and is covered by the upper lid during blink
5. Check if the lens remains on the cornea in all positions of gaze and doesn’t cross the limbus
6. Look at movement on blink which should be 1-1.5mm in the vertical plane (too much may also be because of lacrimation from first time RGP wear)
7. When the lids are held apart the lens should slowly decentre down
8. add NaFl to superotemporal bulbar and If the lens is not already well centred then centre the lens into primary position and assess fit
9. A good fit/well aligned RGP should have central alignment or slight apical clearance, mid peripheral alignment and 0.5mm edge clearance. A flat fit will have central touch and excess clearance, a steep fit will have a central pool of NaFl including possible air bubbles with mid peripheral excessive touch and minimal clearance. Can use Guillon scale for vertical and horizontal, central, mid peripheral and edge clearance +2/+1/0/-1/2 with 0 being ideal and + being too much NaFl and - too little

Question 3

How to alter RGP if decentred?

Question 4

How to alter RGP if excessive/minimal movement?

Question 5

How to alter RGP for more comfort?

Question 6

How are BOZD and BOZR related?

Question 7

How is BVP related to changing an RGP lens fit?