Pres Flashcards
(32 cards)
all binocular summation/stereo is lost in CL pts w/ adds greater than what power?
+2.00D. Start to lose for middle and high SF ~+1.50D
adaptation for monovision fit?
2 weeks; try to discourage night driving or comparing eyes - give realistic expectations
T/F: 0.25D change makes a huge difference in vision w/ bifocal CLs
true. SMALL steps at a time - RTC 2-3 wks to reassess
two multifocal CL systems? which is easier to fit?
simultaneous: look thru all parts of lens @ all times - must decide which to focus with - easier to fit than alternating
alternating: two distinct D vs. N systems - more challenging (prism ballast)
fused GP bifocal designs use different ____, one-piece designs use different ____ - which is more popular?
indices (of refraction); curvatures - more common
alternating design GPs have WHAT to maintain rotational stability? - how much thickness is added per diopter of prism?
- prism ballast (1-3.5 P.D.)
0. 10mm
alternating fitting goals:
- position on ___ lid
- t/f: lens should move down when the eye looks down
- how much of the pupil needs to be covered by the near zone for optimal near VA?
lower
- FALSE: lens should stay on lower lid–> eye moves down, lens translates up
- 80%
more alternating fitting goals:
- the seg should be near the ____ pupil margin (pri. gaze)
- should be within __mm
- allow for (nasal/temporal) rotation
- inferior
- 2mm - but really, that’s way too low
- nasal (eye moves nasal and downward when reading)
- -> temporal rotation = detrimental to VA
3 ways to improve translation:
- flatten BC
- increase prism ballast
- increase truncation (keep lens on lower lid and prevent from sliding under)
where is the distance power in a front aspheric lens?
-becomes more ____ as you go toward periphery
distance: in the center
- plus (add it toward the periphery) - may be affected by small pupils
where is the add power on a single aspheric lens?
-should this type of lens be fit steeper, flatter, or on-K?
on the single aspheric back surface of the lens
-STEEPER - d/t asphericity/eccentricity of back surface
Bifocal SCLs tend to have near in (center/periphery), while bifocal GPs have near in the (center/periphery) - what’s the main factor why this is the case?
SCLs: near in CENTER
GPs: near in PERI
-driving factor - TRANSLATION. In GPs, dist is in center b/c when pt looks down they can see at near (d/t good translation - it’s lacking in SCLs)
how many presbyopes are there in the U.S.?
140 million; very small percentages of pts wearing monovision or multifocal CLs!
Give 2 important POSITIVE Hx factors:
Give 1 important NEGATIVE Hx factors:
Positive: MOTIVATION, REALISTIC expectations. Also- moderate VA demands, hate specs, etc.
Negative: UNREALISTIC EXPECTATIONS, excessive critical visual demands, low illumination env.
biggest advantage to multifocal lenses?
binocularity; stereopsis maintained
fitting procedure: bifocal lenses
- check (mono/binoc) VA first
- T/F: subjective VA more important than actual (w/i limits)
- use ____ room illumination
- trial lens outside phoropter/change in (large/small) increments
- how long is the adaptation period?
- binocular VA first
- True
- moderate illumination
- SMALL (0.25D) changes - make big difference
- 2-3 week adaptation period
Prism ballasting is used in alternating designs; what other property is used extensively to provide rotational stability in an alternating design?
-is this more beneficial for (+) or (-) lenses?
truncation - chop off bottom to align it w/ lower lid and allow it to rest on lid
-better for (+) lenses - edge becomes thicker the more you chop off
where should you put the seg line on an alternating design?
-may be adjusted to ensure at least ___% of pupil is looking thru near zone after translation
near the vertical CENTER of the lens
-80%
A (flat/steep) lens promotes good translation - by how much should you flatten or steepen?
flat = GOOD translation
-flatten lens by ~0.50D
Will a large LD promote or impair good translation?
-what’s the limiting factor?
Large LD –> LIMIT translation
-once the lens hits the UPPER LIMBUS, it can’t move up any higher
Troubleshooting Segmented (alternating vision) lenses:
- poor DIST VA - what to do?
- poor NEAR VA - what to do?
poor DIST - ensure sitting on LL, truncate the lens, increase LD
poor NEAR - improve TRANSLATION
three ways to improve translation? [FIT]
FLATTEN BC, INCREASE prism ballast, Truncate lens
FRONT surface aspheric:
- (dist/near) in center, (dist/near in periphery)
- fit on ____ K (like SV lenses)
- OR @ (dist/near), and use the SAME OR for dist and near!!
- Are they pupil-size dependent?
Dist in center, Near at periphery
- FLAT K; aspheric front surface provides add power
- OR @ Dist; use the SAME OR for D+N
- yes! smaller pupil - less add to look thru
Would you expect a BACK aspheric to align well on the cornea? Why/Why not?
NO; back surface is what’s highly eccentric on a back aspheric - WON’T align well b/c the BACK surface is what creates the add (even though most is neutralized by the tear film)
