1. Introduction to Contact Lenses
Amy C. Nau

2. History 1636 described by Descartes
1886 first therapeutic lens to aid healing after cataract surgery
1888 first lens for KC- scleral
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

3. Demographics 32 million Americans wear lenses 98% single vision
2% bifocal
87% soft
12% rgp
1% pmma
66% disposable

4. Lens Parameters junction Peripheral curve D=n’-n/r CT Base curve OZ
OAD
BCR
PCR
Scr
width
Pcr
width

5. 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.

6. Anatomy of the Contact Rx
Brand/BC/power/diameter
Brand/BC/power/diameter/oz/ct/peripheral curve details/material

7. 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

8. Lens Designs Aspheric Ballasted (prism) Fenestrated
Peripheral only, total, bi(posterior OZ/ant pc)
Ballasted (prism)
Fenestrated
Lenticular (aphakia)
Toric
FST, BST, Bi
Truncated

9. Lens Materials RGP PMMA Silicone acrylate Dk 15-55
Fluoropolymer (FLP) Dk up to 150
Excellent wettability
Deposit resistant
(non silicone polymers)
Soft
HEMA (hydroxyethylmethacrylate)
Absorbs water. 10% increase = doubles Dk
Water content 37-79%
Silicone Hydrogel
Siloxane + cross linker
Hydrophobic
Reduced water content

10. Instruments Keratometer Lensometer- convex side up (bvp) Slit lamp
Topography
Radiuscope
CL comparators-project image 20x
Thickness gauge

11. Patient Evaluation Contraindications 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?

12. History Full medical hx Ocular hx Medication hx Contact lens hx
Spectacle hx
Hobbies/occupational needs
Motivation

13. Conditions that cause problems
Chronic allergy
Dry eye
GPC
Recurrent infections
Sometimes prior sx
Neovascularization
Sometimes strabismus
Pregnancy
Antihistamine use, OCP
Mental status
Age +/-
Lens noncompliance

14. 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

15. Lens Selection Motivation Current lens problems= need to solve
Occupational needs
Cosmetic needs
Maintain health of eye
Cost
Compliance

16. 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

17. 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 to 15.00mm
Tyler’s quartery is an invaluable resource

18. Soft Classifications Water Content Manufacturing process Lens design
Low 37-45% (DW); medium 46-58%; high 59-79% (EW)
More water = thicker
Ionicity
Manufacturing process
Spin casting, lathe cutting, cast molding
Lens design
Function (DW, EW, prosthetic etc)
Color
Bifocal/monovision
Therapeutic (bandage, cosmetic
Aphakic
Toric (double slab off, prism ballast, truncation)
Thickness

19. Extended Wear 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

20. F/U visit for EW Acute hypoxia (CLARE) Microcystic edema GPC K neo
Striae
Infiltrates
SPK
If found, d/c EW.

21. Soft fitting evaluation
Well centered
0.5 to 1.0mm movement with blink
Limbal coverage (at least 1.0mm beyond)
Stable vision
Three point touch

22. 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

23. 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

24. CL problem
RX:
OD: x 165
Os: x 180

25. RGP lenses- fitting philosophies
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

26. 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

27. RGP fitting- determining lens power and base curve
Must have MR and Keratometry

28. RGP fitting- problem

29. 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.

30. 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

31. Solutions/Lens Care
Wetting agents- reduce wetting angle making lens more comfortable (rgp) q

32. 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.