+

CONTACT LENSES

Cara Morris, OD, FAAO

+Types of Contact Lenses

Soft Silicon Hydrogels Hydrogels

Gas Permeable

Hard (PMMA ) not used anymore

Hybrid Synergeyes (RGP in center and a hydrogel skirt)

+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.

+Soft Contact Lenses

Designs: Spherical: use when cyl of the MR is ≤ -0.75 Toric: should be fit when cyl of the MR is -1.00 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

+Parameters of a SCL

Base Curve 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 13.8 -14.4 Certain brands allow you to customize the diameter

Power

+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 ≤ -0.75 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

+Fitting Soft Contact Lenses

Spherical Fitting: Find the spherical equivalent of the MR Vertex all SE +/- 4.00 (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.

+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 -100-125x180, laser mark rotated 10 degrees to

the left, the resultant CL Rx would be: -100-125x010 If the laser mark is rotated right subtract the rotation to the

axis.

+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

+Soft Contact Lenses

Types: 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.

+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

+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:

+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

+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 -100-100x180 and Ks are 4200/4300@090, 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

+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)

+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.

+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

+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.

+Sample RGP Problems

Ks: 42.50/44.00Mr: +1.00 + 1.50 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: 44.00/45.25Mr: -2.00 -1.25 x 180

You want to fit on K: Rx is:

You want to fit .50 flatter than flat K: RX is:

+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.

+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

+RGP Parameters

+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)

+RGPs

Insertion and removal 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

+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.

+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.

+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.

+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.

+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

+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

+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

+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