Download Introduction to Contact Lenses

Introduction to Contact Lenses
Amy C. Nau
History
• 1636 described by Descartes
• 1886 first therapeutic lens to aid healing after
cataract surgery
• 1888 first lens for KC- scleral
• 1899-1912 first concepts of the corneal lens
• 1930’s non glass materials
• 1948 corneal lenses developed
• 1950’s hydrogels
• 1970’s rgp
• 1990’s silicone hydrogel materials
Demographics
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32 million Americans wear lenses
98% single vision
2% bifocal
87% soft
12% rgp
1% pmma
66% disposable
Lens Parameters
junction
Peripheral curve
D=n’-n/r
Base curve
CT
BCR
PCR
Pcr
width
Scr
width
OZ
OAD
Lens Parameters
Saggital Height
BC 6.5
BC 8.1
diameter
If diameter is constant, decreasing the base curve (steeper) increases the saggital
Height. Aspheric lenses have reduced saggital depth compared to spherical lenses.
Anatomy of the Contact Rx
• Brand/BC/power/diameter
• Brand/BC/power/diameter/oz/ct/peripheral
curve details/material
Oxygen
• Dk- measures oxygen permeability of a
material. D= diffusion coefficient for
oxygen movement in the material
k=solubility constant of oxygen in material
• Dk/t= the Dk value divided by the center
thickness (t). Measures oxygen
transmissibility
Lens Designs
• Aspheric
– Peripheral only, total, bi(posterior OZ/ant pc)
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Ballasted (prism)
Fenestrated
Lenticular (aphakia)
Toric
– FST, BST, Bi
• Truncated
Lens Materials
• RGP
• PMMA
• Silicone acrylate Dk
15-55
• Fluoropolymer (FLP)
Dk up to 150
– Excellent wettability
– Deposit resistant
– (non silicone
polymers)
• Soft
• HEMA
(hydroxyethylmethacry
late)
– Absorbs water. 10%
increase = doubles Dk
– Water content 37-79%
• Silicone Hydrogel
– Siloxane + cross linker
– Hydrophobic
– Reduced water content
Instruments
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Keratometer
Lensometer- convex side up (bvp)
Slit lamp
Topography
Radiuscope
CL comparators-project image 20x
Thickness gauge
Patient Evaluation
• Contraindications
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Chronic blepharoconjunctivitis
Recurrent/inflamed pterygium or pinguecula
Bells Palsy with corneal anesthesia
Poor hygeine
Chemical exposures
Severe allergy
Inability to handle lens
Very dry eye
TED
Uncontrolled Dm
AIDS?
History
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Full medical hx
Ocular hx
Medication hx
Contact lens hx
Spectacle hx
Hobbies/occupational needs
Motivation
Conditions that cause problems
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Chronic allergy
Dry eye
GPC
Recurrent infections
Sometimes prior sx
Neovascularization
Sometimes strabismus
Pregnancy
Antihistamine use, OCP
Mental status
Age +/Lens noncompliance
Physical Examination
• Visual acuity / MR
• Lid assessment (include upper and lower
tarsus), blink patterns, mgd/bleph, apeture
• Basic dry eye workup (tbut, LG, NaFl,
Zone quick)
• Corneal status/health, esp epi, old scars
and neo
• Pupil size, HVID
• Keratometry/corneal shape
Lens Selection
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Motivation
Current lens problems= need to solve
Occupational needs
Cosmetic needs
Maintain health of eye
Cost
Compliance
Selection Process- Advantages
and Disadvantages
• SOFT
• RGP
Once the modality is selected, next step is to pick the material and the solution
Finally, brand and power
Soft Lenses
• BC range 6.0 to 11.0 but most are 8.4 to
9.0
• Power range -55D to +60D but most are
+/- 10D
• Diameter 11.0 to 24.00mm but most are
13.00 to 15.00mm
Tyler’s quartery is an invaluable resource
Soft Classifications
• Water Content
– Low 37-45% (DW); medium 46-58%; high 59-79% (EW)
– More water = thicker
– Ionicity
• Manufacturing process
– Spin casting, lathe cutting, cast molding
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Lens design
Function (DW, EW, prosthetic etc)
Color
Bifocal/monovision
Therapeutic (bandage, cosmetic
Aphakic
Toric (double slab off, prism ballast, truncation)
Thickness
Extended Wear
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Use with caution
Make sure eye is healthy
Compliant pt
Understand and accept risk
Willing to have regular f/u
Willing to remove lenses and wear glasses
if needed.
Remove q6, clean leave out for 24 h if possible then reinsert
EW risk of UK 20.9/10K versus 4.1 per 10K
F/U visit for EW
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Acute hypoxia (CLARE)
Microcystic edema
GPC
K neo
Striae
Infiltrates
SPK
If found, d/c EW.
Soft fitting evaluation
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Well centered
0.5 to 1.0mm movement with blink
Limbal coverage (at least 1.0mm beyond)
Stable vision
Three point touch
Troubleshooting
• Decentration- steepen bc or increase diameter,
no spin cast lenses
• Late decentration- look for deposits, GPC
• Minus OR- flatten BC
• Unstable VA- flatten BC if sphere (flexure)
– Tight lens clear after blink, loose lens burred after
blink
• Unstable VA (toric) steepen BC, increase
diameter, change modality
• Too tight- flatten BC or reduce diameter
Follow up
• Be clear about lens regimen
• Make sure they can I/R
• F/U usually about 3-4 weeks with cls on
4+hours
• VA, OR, fit assessment, remove lens,
examine for problems, stain with NaFl
CL problem
• RX:
• OD: -6.75-2.75x 165
• Os: -8.00-0.75x 180
RGP lenses- fitting philosophies
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Small and thin-max tear circulation and oxygen
Vault apex
Small cornea= steep; large cornea = flat
Small and steep lens ; large and flat lens
On flat K
Steeper or flatter than K
IP, bit steeper than K, smaller diameter, thin
edges
• LA (increased comfort); flatter than K, larger
RGP fitting technique
• Select the fit you want to use for the pt
based on physical exam, MR and K.
• Select diagnostic lens if available,
evaluate fit, perform OR.
• Select material you want to use
• Select care regimen
RGP fitting- determining lens power
and base curve
• Must have MR and Keratometry
RGP fitting- problem
RGP fit- troubleshooting
• Discomfort- lens edge (too thick, too sharp, poor blend)
• Excessive movement- too flat, limbus irritated. Steepen
bc or increase diameter.
• Too tight- edema, discomfort, redness. Flatten BC,
decrease diameter, flatten PC
• Vision-OR, flexure, decentration, deposits, incorrect
power
• Poor wetting d/t partial blink
• Deposits- enzyme, surfactants, change material, plasma
tx
• Flexure- Over K, increase CT, stiffer material, reduce
OAD, reduce OZ
• Solution hypersensitivity- try one with different
preservative.
Solutions/Lens Care
• Surfactants to solubilize debris/mucous/lipids.
Remove surface contaminants. RUB and
RINSE off.
• Disinfection-killing infectious organisms
– Chemical,hydrogen peroxide, thermal, UV
• Enzyme cleaners remove deposits chemically
bound to the lens (lipoprotein, denatured
lysozyme)
– Papain, pancreatin, subtilisin
Solutions/Lens Care
• Wetting agents- reduce wetting angle
making lens more comfortable (rgp) q
Follow up
• Lens care regimen, insertion and removal
and wearing schedule should be outlined
• F/U in about one month with cls on 4h
• Visual acuity, OR, lens evaluation, remove
lens and evaluate eye.