What is Conforma-K™?
The Conforma-K and EllipSeeCon-K designs have an ellipsoidal posterior surface that gradually flattens in all meridians from the optic center to the lens edge.
This progressive flattening minimizes localized bearing points resulting in improved alignment and comfort. Improved lens to cornea alignment provides a more uniform tear film and efficient masking of irregular astigmatism. Traditional multicurve Keratoconus designs flatten in multiple steps creating numerous potential pressure points resulting in tear film and comfort obstacles. With Conforma-K these fitting obstacles are minimized.
Conforma-K lenses will provide the design and material combination that will reduce the challenge and increase your success rate. Conforma-K lenses are only available in the Boston ES® and Boston XO® materials. Ellip-See-Con-K (ESC-K) is the same geometry as Conforma-K but is available more material choices.
Conforma-K Lenses provide even distribution of bearing pressure.
The aspheric posterior surface of the Conforma-K lens not only enhances the lens to cornea fitting relationship, it also provides a larger functional optic zone reducing flare and ghosting. The aspheric surface also minimizes peripheral aberrations and residual astigmatic error. Conforma-K lenses will normally center over the apex of the cone but the large optical zone area will normally provide ample pupil coverage.
How can one eccentricity fit most corneas?
Conforma-K corneal lenses are available in a .65 eccentricity (peripheral flattening factor). However, using the same eccentricity value but changing the base curve value also changes the peripheral flattening since the base curve denotes the magnitude or size of the ellipse (hence, a steeper base curve will have a slightly steeper periphery and, conversely, a flatter base curve will have a flatter periphery).
No pronounced junctions
or pressure points.
*Maximum pressure during lid
closure at multi-curve junctions.
Fitting Conforma-K GP Lenses
A trial fitting is essential for your Keratoconus patient. If your patient is not wearing a GP lens, you will have to rely on Topography of Keratometry findings to select an intial trial lens.
1. Select a base curve .50 diopters flatter than the average "K"
Example: 45.00 / 50.00 Keratometer Readings
47.00 (7.18) Base Curve
This is only a suggested started point. Traditional keratometry readings can serve as a reference but are usually of little value in determining the final base curve selection. The keratometer measures approximately 3mm of the central cornea. The cone is normally inferior and generally much steeper than the central and superior sections of the cornea. A successful fit must be based on your observations of the fluorescein pattern, lens movement, position and visual accuity. A gross observation of your trial lens should be made to evaluate generalposition and movement. Low riding lenses are not uncommon on cone patients and should not be rejected based on position alone. If a lens is generally centered over the pupil and lens movement is not excessive, you are now at a point where a more critical evaluation should be accomplished with a Burton or Slit lamp. Acceptable lens position and movement would maintain the visual axis within the optical zone. Decentration or movement resulting in an interruption in vision, would not be acceptable.
2. Observe Central fluorescein pattern. Minimal clearance to light touch at the apex of the cones should be the objective. (See Figure 1)
Fluorescein should be used to closely evaluate the fitting relationship of your trial lens. An acceptable fluorescein pattern would show minimal clearance to light touch at the apex of the cone. A three point touch would be acceptable, light touch at the apex and mid-periphery.
Adjacent to the cone, fluorescein will generally form a surrounding band of pooling. This pooling should begin to thin as the lens surface comes into closer alignment at the mid-cornea. 360 degress of peripheral edge lift should be present with no seal-off points. Apex touch should be minimized.
3. A flat fitting lens could display any or all of the following symptoms. (See Figure 2)
A. Harsh or broad area of apical touch
B. Excessive peripheral stand-off or pooling
C. Excessive movement or displacement with blink
If your trial lens demonstrates any of the above symptoms, begin steepening the base curve in 0.50 diopters steps as required. Diameter and peripheral curve changes will also influence lens lift.
Controlled Edge Lift
The Conform-A-Spheric will help the lens fitter control edge lift and tear exchange. There are three edge lift options available, CAS 121, 141, 161. The CAS 121 is the steepest of the 3 and will reduce edge lift and tear exchange. The CAS 141 is a mid range appropriate for the average fit. The CAS 161 is the flattest of the 3 and will increase edge lift and tear exchange.
4. A steep fitting trial lens could display any or all of the following symptoms. (See Figure 3)
A. Excessive apical clearance or central pooling.
B Trapped bubble adjacent to the cone.
C. Mid-peripheral seal-off.
D. Lack of lens movement.
Base curve flattening in 0.50 diopter steps will be your most effective change to loosen a tight fitting lens. A diameter or optic zone reduction, as well as a flatter peripheral curve, could be used to loosen a tight fitting lens.
Once an acceptable fit is achieved, over refract to determine the final lens power. Residual cylinder may be present, but all attempts should be made to avoid complex toric designs. Whenever possible, your best spherical over-refraction should be used to determine the final lens power.
Controlled Edge Lift
The Conform-A-Spheric will help the lens fitter control edge lift and tear exchange. There are three edge lift options available,CAS 121, CAS 141 and CAS 161.
The CAS 121 is the steepest of the 3 and will reduce edge lift and tear exchange. The CAS 141 is a mid range appropriate for the average fit. The CAS 161 is the flattest of the 3 and will increase edge lift and tear exchange.
The two ellipses have the same eccentricity and are identical in shape, one is twice the size (linear dimension) of the other. The magnitude of the larger, given by r (base curve radius) is twice that of the smaller. Note how a change in base curve or overall lens size will affect peripheral fit.
Conforma-K lenses with .65 eccentricity allows the lens to be fitted appreciably steeper for better centration while the less curved periphery is directed in a more downward, long, cone-like direction, thus paralleling the anomalous cornea.