EST: SCL FITTING

Question 1

state how to calculate initial BC, power (sph equivalent?), diameter for conventional SCL

Answer 1

initial BC: flatter K + 0.8mm
e.g k reading: 7.5mm @ 90, 7.6mm@ 180
BC: 7.6 +0.8 = 8.4

power: use conversion table if rx >/= 4.00D
*consider sph equivalent id sph is -0.50 or -0.75 DC
sph+ 1/2 cyl

diameter: HVID+ 2mm

Question 2

state how to calculate initial BC, power (sph equivalent?), diameter for disposable SCL

Answer 2

BC and diameter depend on brand + availability. Mostly BC: 8.5/9.0 (acuvue)

power: use conversion table if rx >/= 4.00D
*consider sph equivalent id sph is -0.50 or -0.75 DC
sph+ 1/2 cyl

Question 3

how should calculate power for toric scl for both conventional and disposable lenses?

Answer 3

Exact or closest SCL power to the Subjective Rx available
Ideally, the EXACT CYL power & axis

To consider vertex conversion for both the SPH & CYL meridian (if Rx ≥ ±4D)

Eg: SPX : -6.00 / -2.00 x 180 = SCL : -5.50 / -1.75 x 180

Question 4

how to calculate corneal astig?

Answer 4

diff in power seen in K reading
e.g K1: 41D @ 180, K2: 42D @ 90

CA: -1.00 x 180 (flatter meridian)

Question 5

what is the most likely PUT% for ideal, loose and tight lenses?

Answer 5

ideal: easy to dislodge and smooth recovery, 40-60%
loose: move easily, long recovery <35%
tight: more resistance, will not move easily, 70% ok > 70% not ok

Question 6

when is over rx done? how do we calculate expected over rx?

Answer 6

done when trial lens power not the closest to rx.
or when px comes for after care with complaint of blurry vision

calculating over rx:
take initial trial minus degree that is being fitting on patient

how to check for over rx?

1. take VA with lens in eye
2. 0.25 challenge
3. give max plus
4. bino balancing

Question 7

what are some likely causes of subnormal VA after over RX?

Answer 7

axis is off
degree is off

wait for px trial lens to arruve

Question 8

how is axis rotation compensated for?

Answer 8

1. measure and record amount of rotation using slit lamp
2. check if there is reduced VA
3. if VA reduced, compensate using LARS
   left add, right subtract

Question 9

what are the parameters of disposable SCL? (power, cyl power and axis)

Answer 9

power: +6.00 to -6.00 in o.25 steps, -6.50 to -10.00 in 0.50 steps

cyl power: -0.75, -1.25, -1.75, -2.25

axis: in 10 deg steps