1. CONTACT LENSES
Cara Morris, OD, FAAO

2. Types of Contact Lenses
Soft
Silicon Hydrogels
Hydrogels
Gas Permeable
Hard (PMMA ) not used anymore
Hybrid
Synergeyes (RGP in center and a hydrogel skirt)

3. Soft Contact Lenses Different Properties of the SCL material:
Water Content
Low water: the SCL material is less than 50% water
Less deposits
Dehydrate less on the eye, so better for dry eye patients
Available in Hydrogel and Silicon Hydrogel material
High water: SCL material is more than 50% water
Opposite of low water
Available in Hydrogel material
DK: oxygen permeability
Hydrogels: have low DK
Silicon Hydrogels: have a high DK
The higher the RX, the lower the DK will be. A minus lens will be thicker in the edges, so neovascularization more prominent. A plus lens thicker in the center, so corneal hypoxia more of a concern.

4. Soft Contact Lenses Designs: Types of SCLs:
Spherical: use when cyl of the MR is ≤ -0.75
Toric: should be fit when cyl of the MR is or greater, or when a spherical lens does not provide acceptable vision with low amounts of cyl
Bifocal: Can be fit on presbyopic patients or young patients with accommodative insufficiency
Types of SCLs:
Silicon Hydrogels: newest available lens
Have a high DK
Normally have low water content
Hydrogels (HEMA)
Have a low DK

5. Parameters of a SCL Base Curve Diameter Power
The larger the number of the BC, the flatter it is.
Ex: 8.6 BC is flatter than an 8.4 BC
Diameter
Usually range from
Certain brands allow you to customize the diameter
Power

6. Fitting Soft Contact Lenses
Determine the patient’s MR and convert to MINUS cylinder
Determine the patient’s K’s.
Fit a spherical lens if the patient has ≤ of cyl
Use a flat Base Curve lens for K’s ≤ 44.00
Use a steep Base Curve lens for K’s over 44.00

7. Fitting Soft Contact Lenses
Spherical Fitting:
Find the spherical equivalent of the MR
Vertex all SE +/ (you will subtract if - Rx, and add if + Rx)
Check movement and centration. You want some movement but not excessive amounts. Centration does not have to be perfect, but you want full limbal coverage and no buckling of any edges. If lens buckles, the lens is too flat. (only really seen with really flat corneas s/p some corneal surgeries)
Check vision and perform Spherical OR. Can perform a SCOR if vision not adequate (20/25 or better). Could then switch to a toric if vision not adequate with a spherical lens.

8. Fitting Soft Contact Lenses
Toric Fitting
Convert to Minus Cylinder
Vertex the Rx
Check for adequate movement
Should have good centration for best vision
Check for rotation by observing the laser mark.
Use LARS to adjust axis (left add, right subtract)
If the laser mark is rotated left, add the rotation to the axis of the MR (not the contact lens rx)
MR is x180, laser mark rotated 10 degrees to the left, the resultant CL Rx would be: x010
If the laser mark is rotated right subtract the rotation to the axis.

9. SCL Fitting Trouble Shooting
If lens too tight or no movement: flatten the base curve
If lens moves too much: steepen the base curve
Poor centration: steepen the base curve
Lens too small or not enough limbal coverage: switch to a larger diameter lens
Patient complains of fluctuation in vision, with vision the best right after the blink: the lens is probably too steep, flatten the BC

10. Soft Contact Lenses Types: Toric CLs:
Disposable: daily, 2 weeks, monthly, 3 months
Non Disposable: annually (not as common anymore)
Toric CLs:
prism ballast: bottom portion of the lens is thicker to keep the lens from rotating.

11. Soft Contact Lens: I and R and care
Insertion/Removal
Inserted directly on cornea.
Having the finger dry and CL wet helps with insertion.
Remove by sliding lens off the cornea and pinching the lens off the inferior conj.
Cleaning:
Multipurpose solution for cleaning, disinfecting, storing (should rub lenses daily with soln, though advertised as no rub most of the time) (Optifree, Renu)
Separate Cleaners available for annual replacement lenses or patient’s that have lots of protein deposits. Must rinse well with saline
Clearcare: an H2O2 system

12. Gas Permeable Contact Lenses
Types:
Gas Permeable or “RGPs”
PMMA or “hard” CLs
Most materials have a high DK
Properties
DK: oxygen permeablility
PMMA has no DK thus caused cornea anoxia and corneal warpage
GP materials now have very high DK
Wetting Angle:

13. Fitting Gas Permeable Contact Lenses
Types:
Spherical: use if corneal cyl and MR cyl match
Bitoric: use if over 3 of cyl for stabilization of the lens
Reverse Geometry: use for post RK/Lasik/PKP patients
Keratoconus
Bifocal/Multifocal: presbyopic
Scleral: for patients with irregular corneas not tolerant or not fittable in RGPs

14. Fitting Gas Permeable Contact Lenses
Convert MR to minus cylinder
IF fitting ON K: this means fitting on the flat K. The spherical component on the MR in – cyl corresponds to the flat K. So, MR is x180 and Ks are the resultant RGP BC and power would be 4200/-1.00
Need to vertex the spherical component on the MR if over 4.00D.
Assess movement: An RGP should move with a blink to allow tear exchange.
Assess fluorescein pattern

15. Fluorescein Patterns Alignment: a uniform and thin fluorescein pattern
Steep: the center of the lens shows pooling of fluorescein.
Flat: the center of the lens shows no fluorescein and is dark.
WTR astigmatism: fluorescein will pool in the steeper part of the cornea thus showing pooling vertically.
ATR astigmatism: fluorescein will pool horizontally. (looks like bow tie)

16. Fitting RGPs
After assessing the fluorescein patterns, determine if you need to adjust the BC. Use SAM and FAP to adjust power when adjusting the BC.
SAM: If steeping the BC, you need to add minus to the rx
FAP: If flattening the BC, you need to add plus to the rx
Centration
Vertical: ok if lid attachment (the lens rides under the upper lid and rests there in primary gaze) or interpalpebral, should not touch the lower lid
Horizontal: as close to centration as you can to keep OZ in pupil.

17. Fitting RGPs Check vision and perform an OR Adjust the power as needed
Wearing time: Usually for a few hours the first day, then increase by 1-2 hours a day. May take a couple weeks to adjust to a full day of wearing an RGP

18. SAM and FAP
SAM: if you Steepen the base curve, you have to ADD Minus. This is because a steeper BC causes a tear layer that will add plus power overall, so minus power needs to be added to the final RX .
FAP: if you Flatten the BC, you have to Add Plus. When you flatten the BC, this causes the tear layer to add minus power overall, so plus power needs to be added to the final RX.

19. Sample RGP Problems Ks: 42.50/44.00 Ks: 44.00/45.25
Mr: x 180
You want to fit on the flat K: resultant RX is:
You want to fit 0.50 steeper than flat K: Rx is:
Ks: /45.25
Mr: x 180
You want to fit on K: Rx is:
You want to fit .50 flatter than flat K: RX is:

20. Fitting Gas Permeable Contact Lenses Trouble Shooting
Poor Centration
Increase the diameter or OZD
Steepen the BC
Or switch to a toric SCLs
Poor movement
Flatten BC
May have seal off, so flattening the peripheral curves as well.

21. Gas Permeable Design Components of a GP:
Base Curve (or Posterior Central Curve Radius (PCCR))
Back Vertex Power (or just the Power of the Lens)
Total Diameter
Peripheral Curves
Posterior secondary curve and width
Posterior peripheral curve and width
Posterior Optic Zone Diameter
Center Thickness
Anterior Optic Zone Diameter

22. RGP Parameters

23. Measuring RGPs Base Curve: Radiuscope Diameter: Reticle Magnifier
Power: Lensometer
Peripheral Curves: radiuscope
Peripheral Curve Widths: reticle magnifier
Optic zones: reticle magnifier
Center thickness: lens clock (lens is place concave up. 1 diopter reading is equal to 0.1mm thickness)

24. RGPs Insertion and removal Cleaning Insert onto cornea
Remove by blinking out by catching the edges of the RGP on the lids or remove with a plunger
Cleaning
Cleaner at every night, rinse with water or saline, store in a conditioning solution
Multipurpose solutions also available for RGPs now

25. Misc. RGP info
If you increase the diameter of a lens, this will cause the lens to be tighter. (increasing the diameter increases the vault, which will tighten the lens)
If you were to change the diameter of a lens, need to adjust the BC the keep the same corneal relationship. Ex if a 9.2diameter “X” BC looks great, but want to try a 9.6 diameter lens, must flatten the BC by 0.25D to keep the same RGP/corneal relationship.

26. Contact Lens Terminology
Truncation
Removing the lower portion of the lens to create a straight edge. This edge will rest on the lower lid. Seen in bifocal RGPs and possibly soft toric
Vault or sagital depth
The distance from the lens center to a flat surface. A flatter BC would be closer to the surface, thus have a smaller vault.
Fenestration
A ventilation hole drilled in a contact lens. Provides additional oxygen to the cornea and may assist the dispersal of air bubbles or dimple.

27. Contact Lens Terminology
FLARE:
Peripheral blur, usually experienced by hard lens wearers as a reflections or halation around the edge of the contact lens.  Caused by decentration or too small a POZD and therefore worse with large pupils.
RADIUSCOPE:
Instrument used to measure the radius of curvature of a contact lens (Base Curve). The larger the radius, the flatter the BC.
REVERSE GEOMETRY LENS:
A lens where the second radius is steeper than the base curve.    Such lenses are used mainly for orthokeratology but also for other fitting applications such as corneal grafts and post refractive surgery.

28. Contact Lens Terminology
SPECTACLE BLUR:  Blurred vision with spectacles after wearing contact lenses because of edema and corneal molding.  Mainly caused by PMMA but also encountered with hard gas-permeable and soft lenses.
Wetting Angle: the wetability of a contact lens. The lower the angle, the better the contact lens wets.

29. Presbyopic CL patients
Monovision
Dominant eye is for distance.
The other eye is focused for a near distance.
Disadvantages:
Night time driving difficulty
Reduced stereopsis
Bifocal Contact Lenses
Blur at some distance, vision just not as clear as distance with readers
Reduced contrast sometimes
Distance Contacts with readers

30. Bandage Contact Lenses
Used for:
Healing and Protection
Abrasion
exposure
Comfort
For dryness
For exposure
Drug Reservoir
Use a Soft Contact Lens with:
High DK, low power, steep BC to minimize movement

31. Extended Wear Contact Lenses
Fitting
Available as 6 day wear or monthly wear
Should fit with highest DK
Fit with a loose lens
Complications
Increased redness
Corneal anesthesia
Corneal edema which can cause increase in myopia

32. Contact Lens Complications
Neovascularization
Occur from lack of oxygen to the cornea (Hypoxia)
Minus lenses are thicker in the periphery increasing risk of neovascularization
GPC
Protein deposits on the lens can irritate the palpebral conjunctiva
Switch to a daily disposable, use mild steroids or MCS drops, reduce wear time, compliance
Corneal edema
From overwear, extended wear, thick plus lenses, low DK lenses
Ulcers/infiltrates
Tight lens syndrome
The lens is too tight and sucked on, caused lots of pain, photosensitivity.
Will see SPK, imprint of CL on conj, corneal edema