RGP Design Flashcards
Three things lens design should provide to pt:
comfort, vision, minimal surface changes
Four things to look for in evaluating lens fit [PCM] ..and L
position, centration, mvmt, lens-to-cornea relationship
Specifications of design Rx: remember your mnemonic!
B-CLOS-PC-BETM
-BC/CLP/LD/OZD/Scr @w/Pcr@w/CT/Blend/Edge lift/Tint/Material
OZD: 1.5 more than BC
Blend: 3.0 more than BC
What you’ll select FIRST, then second, third, fourth, other: zone s___, c___, l__ p__, c__ t__, o___
(see other sheet)
first: zone SIZE: LD, OZD, SC WIDTH/PC width
second: zone CURVATURE: BC, SCr/PCr
third: lens POWER
fourth: center THICKNESS
last: other - ET, shape, junction blend
last last: material
LENS DIAMETER - choose FIRST! derive others
larger cornea - \_\_\_\_ diameter
-values for HVIDs of 10, 11, 12?
flatter cornea - \_\_\_\_ diameter
steeper cornea - \_\_\_ diameterlarger diameter:
HVID: 10mm - 8.8, 11mm - 9.2, 12mm - 9.6
flatter = larger LD
steeper = smaller LD
OZD - bright/dim light?
-usually how much smaller than LD?
-larger pupil = ____ OZD
NECO starting point?
dim light
~1.5mm smaller than LD
larger
7.8mm
SC WIDTH/PC WIDTH
- larger LD - requires (more/less) curve widths
- SCw usually __X larger than PCw
- What’s the purpose of the PCw?
-MORE curve widths - tri or tetracurve
-SCw = 2PCw
LD = OZD + 2(SCw) + 2(PCw)
PCw - tear exchange!
BASE CURVE - based on what 3 things? [KTT]
KERATOMETRY: Kavg - 0.50 (standard LD =9.2)
-1.00 for 9.6/8.2, -1.50 for 10.0/8.6
TORICITY -more toricity requires STEEPER lens
TOPO - rare - takes ave of 4 readings, 3mm away from apex
T/F: alignment = on-K
-what DOES = on-K?
FALSE
-flat K! - “On-K” = BC equal to flat K
T/F: SCr and PCr are always flatter than the BC
-equation? Add or subtract addnl size?
TRUE - ADD! Larger number = flatter
- SCr = BCr + 1.5mm
- PCr = BCr + 3.0mm
CENTER THICKNESS:
Increased thickness: (better/worse) durability/stability, (increased/decreased) O2 transmission -comfort, (more/less) fitting problems - why?
-What about decreased thickness?
better stability/durability, DECREASED O2 transmission (and comfort), MORE fit problems d/t excessive weight
decreased thickness: worse durability (more fragility), increased O2/comfort, better positioning (lighter)
T/F: You must change the center thickness as the lens power changes in order to maintain the edge thickness
true. absolutely true. Gotta keep that edge the same.
Center thickness increases as the peripheral curves become (flatter/steeper)
- minus carrier lenticular - (thicker/thinner) CT?
- what should you do to CT w/ DK>40?
flatter
thinner (for - lenticular)
increase CT by .03-.04 to increase O2 permeability
EDGE thickness - ideally what range?
Powers greater than -6.00D - what lenticular?
Powers less than -2.00D - what lenticular?
ANY PLUS POWER - what lenticular?
.1-.12mm (happens @ -3.00D); -2–>-6D: single
plus
minus
minus
what’s the ideal edge shape? (t___ edge, r___ tip)
tapered edge, rounded tip
-apex either a) centered or b) more posterior (closer to cornea)
