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L11 Soft + Rigid Contract Lenses - Coggle Diagram
L11 Soft + Rigid Contract Lenses
soft contact lenses
on-eye power change
drape over cornea -> changes in lens curvature -> on-eye power diff from eye
water in lens evaporates -> RI affected -> power
high water dehydrate more/faster
dehydrate more during near work
corneal temp -> hydration + RI
smaller power change for neg lens, cf pos lens
aberrations
sph ab greatest, VA on OC
cf spect lens, obliq astig, distortion, field curve greatest
more sph ab in mesopic + scotopic
transverse chr ab w prismatic effects when obliq view
CL minimal ab, ab of lens balance eye ab
reality
non-modifiable CL, sph ab main ab
on-eye sph ab via lens shouldn't diff from off-eye ab due to flexure, etc
neural component of VA
decent of aspheric CL shouldn't have sig ab
sph ab more neg w age
sph ab same in photopic, diff in mesopic
lens induced sph ab affects myopes more
Aopt: opt lens power adjust to minimise sph ab
plot
sph ab more pos w age, more neg sph ab correction
balance out ab as eye becomes more pos
clinical pearls
aspheric lens w sph ab can correct px sph ab
HOA remain + chr ab blur + sphcyl Rx
astig >0.75D -> sphcyl Rx > HOA
thin CL on-eye SA similar to off-eye SA
lens flexure, hydr change, tear film change
lens-eye WF ab lower w rigid CL
hydrogel lens -> corneal warpage -> ab change
monochr WF ab improvement when large pupil
in meso + sco, spatial vision degrad due to neural than optical
features
little additional asym ab
optic zone diameter exceeds entrance pupil
avoid haloes
minimal fitting problems
less effective for astig
disadvantages
lens flexure
hydration
non-uniform tear film thickness
on-eye power change
rigid contact lenses
basic properties
tear lens dep optic zone geometry
tear lens neg/zero/pos power based on lens fitting
flat -> neg
align -> zero
steep -> pos
basic design parameters
back optic zone radius BOZR + tear lens power
+0.25D for each 0.05mm
back vertex power BVP change
tear film
trial to find BOZR
overrefraction to determine additional power
ordered lens power = BVP + overrefraction
aberration
well-centred -> sph ab main
pupil >6mm + lens power <-3D
ocular WF ab -> cornea + lens
sph ab of eyes opp to lens
corneal + lenticular ab varies, worst w age
if corneal ab reduced, lens ab might persist
CL either reduce/increase HO WF ab cf og eye
px w high corneal ab -> reduced w CL, vice versa
astigmatism
irreg astig
fitting for astig > 2D
toroidal correction
visually disturbance
large pupil diameter -> peripheral light -> blur
decentered
corneal surface not macthing -> peripheral refraction
grime on surface -> blur
other
lens flexure
corneal warpage
aspheric lens
sph ab more pos w age