SCL Fit Char Flashcards
What is required at all times regarding coverage?
FULL CORNEAL COVERAGE
What three factors affect lens position? [SIL]
Sag, LD, lid interaction (tight lids can push down)
- BLINK mvmt: is assessed in ____ gaze. Lag Range?
- UPGAZE mvmt: range?
- is the upgaze blink mvmt ok to be higher than in primary?
- LATERAL LAG range?
PRIMARY: 0.50-1.00mm
- same for upgaze.
- can be up to 2mm in upgaze blink
- LATERAL: 0.50-2.00mm
when is push-up movement used?
when inadequate blink mvmt is noted - check to see if it’s fitting too TIGHT (not gonna move) or LOOSE (move excessively)
-STEEPER BC and LARGER LD will (increase/decrease) lens mvmt
DECREASE
more EYELID interaction will cause (increase/decrease) lens mvmt
-what are two lens characteristics that INCREASE lid interaction? [EMT]
MORE
MODULUS
THICKNESS - increases in EITHER ONE will INCREASE lid interaction (and increase lens mvmt)
what effect happens in each thing below produced by DEHYDRATION of a lens?
-BC? LD? Power?
BC: steepen
LD and power: decrease - power becomes more PLUS
K mires for STEEP lenses usually ___ after a blink, but ___ over time
STEEP: blur-clear-blur. CLEAR after blink - then blur over time
K mires for FLAT lenses usually ___ after a blink, but ___ over time
blur, CLEAR over time (which is why you fit them flat on purpose)
where will a STEEP fit lens produce a retinoscopy reflex distortion?
-how about a FLAT fit lens?
STEEP lens: distortion CENTRALLY
FLAT lens: distortion INFERIORLY (yes, inferiorly…sounds wierd)
What are 3 other observations indicating a steep fit?
bubbles @ limbus, vessel blanching, lens imprint after removal
STEEP lenses AND FLAT lenses have (good/poor) draping over the cornea.
- STEEP lenses: VA WORST (after/before/between) blinks
- FLAT lenses: VA WORST (after/before/between) blinks
POOR draping (both of them). Flat lenses may also move excessively.
- STEEP lenses: bad VA BETWEEN blinks (best VA right after a blink)
- FLAT lenses: bad VA right AFTER blink, then clears as eye stays open
What’s the average NATURAL amt of spherical aberration in the eye? Positive or negative SA?
+0.15 microns (not diopters) - PUREVISION has an adjusted (-0.15 micron) lens to reduce SAs
What is the MOST convenient, MOST healthy lens class?
-What’s the most COST-effective (cheapest) lens class?
1 day CW (10-14 hrs)
1 yr DW (no sleepy!)
what are three “dry eye” materials?
- filcons! [OHD]
- omafilcon
- hioxifilcon
- delefilcon
Parameters: LD
- Average LD? Range?
- Approx __-__ LARGER than HVID
avg: 14.0. Range 13.5-15.0
2-3mm LARGER than HVID, or 1-1.5mm LARGER around limbus (scleral drape)
Parameters: BC. Avg HVID -just use which available BC?
- LARGER HVID - want a (flatter/steeper) BC.
- usually pick a lens ___D (flatter/steeper) than (flat/steep) K
-avg HVID - use avg or “medium”
larger HVID - use steeper BC (larger sag)
smaller - use flatter (smaller sag)
4D FLATTER THAN FLAT K - allow TEAR EXCHANGE!
what is the average HVID? What needs to be used when your pt doesn’t have an avg HVID?
11.8; EFFECTIVE K
What 2 factors does “Effective K” incorporate? It’s all in an effort to assist proper __ selection
- cornea is LARGER than 11.8mm, (add/subtract) WHAT? from WHERE? for every HOW MANY mms larger?
- what if cornea is SMALLER than 11.8?
1) central corneal radius (Ks)
2) corneal diameter (HVID)
- proper BC selection
- LARGER: add 1D to the Ks every .2mm LARGER than 11.8
- SMALLER: subtract 1D from the Ks for every .2mm
What power do you order for a sph-cyl pt w/ minor cyl?
Sph equivalent of the VERTEXED SR
what’s the “normal” CT to order?
0.12 (standard); “thin” = 0.07, “min” = 0.03
what’s the lens equilibration time?
5-30 mins
what two values do you add to determine the FINAL CLP?
OR, CLP. Compare SE to the SRv; SHOULD be equal/within 0.25D
what elements are required in your final SCL order?
BRAND, replacement interval, units - other than that it’s the things YOU decide over:
-BC, Power, LD, tint
First parameter change to make?
-steps usually in __-__ mm increments
BC; 0.3-0.4
Second parameter change to make?
-what must you ALSO change if you do this?
LD: SMALLER if too much coverage or LARGER if too unstable/loose/decentered.
- MUST also change BC! if you INCREASE CT: FLATTEN bc (the opposite! to counter the effect!)
- remember - a FLATTER BC = BIGGER NUMBER)
third parameter change to make? (RARE)
-WHEN do you make it?
CT: hypoxia-related conditions
-or: if it dries too quickly, not enough mvmt, hard to handle
LAST parameter change to make?
- what do you do if the lens dries too quickly?
- what do you do if there’s excessive protein deposit?
- when would you INCREASE water content?
Water content
- LOWER water content
- switch to non-ionic, low water (class 1)
- increase if hypoxia-related probz; OR just change to SiHy
biggest advantages of SCLs?
better INITIAL COMFORT, flexible wear (easier for part-time), convenience, LESS spectacle blur, ocular health)
biggest advantages of GPs?
ACUITY/optics.
-better deposit resistance, durability, FEWER COMPLICATIONS, easier handling/inspection, cheaper!
