Variable Focus Corneal Lens
VFL3 lenses provide an ideal balance of distance, intermediate, and near vision.
This design provides a progressive range of focal powers enabling the presbyopic eye to selectively focus at any distance within the power range of the VFL3 optical system. These lenses are not translating bifocals but rather simultaneous multifocals. Simultaneous in that multiple images are being focused on the back of the eye at one time. The human eye and brain, working together, are capable of interpreting these multiple images. A mental selection takes place and the object being viewed comes into focus, whether at near, intermediate or far. These lenses are capable of focusing at any distance from 40 cm to 20 feet and beyond. Your patients will be able to focus on near reading tasks, or their computer screen, or an object across the street. The lens optical center must be positioned directly in front of the pupil for best results at all distances.
VFL3 multifocals do not have a single add power, but rather a progressive range of add powers from approximately +0.75 to +2.00. This multifocal or variable focus power range will normally satisfy the add requirements of emerging and moderate presbyopes. For advanced presbyopes, VFL 3 with HD Optics, HD-AP or HD-CAP front surface geometry will extend the total add power.
The progressive power gradient of a VFL3 lens is derived from a progressive flattening posterior surface combined with a single spherical anterior surface. The aspheric posterior surface not only contributes to the progressive power effect but significantly influences the fitting approach required to achieve a successful lens to cornea fitting relationship. The sagittal depth of a VFL3 lens is greatly reduced due to the progressive flattening of the posterior surface. Axial edge lift increases as the posterior surface flattens. In order to offset this rapid flattening the apical radius (base curve at it's steepest point) must be fit considerably steeper than the flattest corneal meridian. Most patients are fit approximately 2.75 to 3.00 diopters steeper than the flattest corneal meridian.
In the example, a base curve has been selected 3.00 diopters steeper than the flat "K". A VFL3 lens fit 3.00 diopters steep will align with the intermediate and peripheral corneal surface. A small area of central clearance is characteristic of a normal VFL3 fit. This central clearance forms a significant plus tear lens between the base curve of the contact lens and the anterior surface of the cornea. This plus tear lens must be neutralized by adding an equal amount of minus power to the contact lens. An over-refraction is the most accurate way to determine the required lens power. An approximation of the anticipated lens power can be made by using normal SAM/FAP rules. This plus tear lens compensation is the reason why the power of a VFL3 lens is normally 2.25 to 2.75 diopters more minus than the patient's refractive error.
Example: 43.00@180 / 44.50@090 Keratometer
"K" 43.00 +3.00 = 46.00 D or 7.33mm
SAM/FAP Rules
SAM = Steeper Add Minus
FAP = Flatter Add Plus
Fitting VFL3 Lenses
Steep Fit: Unacceptable
Flat Fit: Unacceptable
Good Fit: Acceptable
Slight inferior position
• Pronounced central pooling
• Harsh intermediate bearing
• Inadequate peripheral clearance
• Flatter base curve indicated
Superior
• Thin pattern over pupil due to decentration
• Excessive peripheral clearance (stand-off)
• Steeper base curve indicated
Well centered
• Slight central pool
• Uniform mid-peripheral alignment
Conforma HD Optics
VFL3 lenses provide an ideal balance of distance, intermediate, and near vision.
In recent years Conforma has developed aspheric anterior surfaces to compliment the optics and expand the add power capability of our traditional VFL3 Multifocals. HD Optics was the first stage in development of our front surface technology. HD Optics minimizes aberrations and maximizes optical quality resulting in improved visual acuity for your patients.
VFL3 Multifocal
without HD Optics
VFL3 Multifocal
with HD Optics
Troubleshooting Lens Position
Select VFL 3 trial lenses based on the preceding base curve chart. VFL3 must center well to achieve best-fit and visual results. If the trial lens doesn't center or moves excessively, steepen the base curve .10mm.
If unable to achieve acceptable centration through the suggested corrective action below, or you would like to discuss other potential parameter changes call Conforma at: 1-800-426-1700
Lens Position:
High Riding VFL3
Superior Position
LENS
LENS
LENS
Lens Position:
Low Riding VFL3
Inferior Position
Lens Position:
Nasal/Temporal
Decentration
Lateral/Medial Position
Cause
Correction
Verify with Fluorescien & Steepen Base Curve .10mm
Lenticular Plus Carrier or C/N
Reduce diameter by .4mm
Add 1.0 Prism BD
Flatten Base Curve .10mm
Flat Base Curve
Thick Minus Edge
Large Diameter & Narrow Aperture
Corneal Topography & Steep Base Curve
Cause
Correction
Verify with Fluorescien & Flatten Base Curve .10mm
Lenticular Minus Carrier
Increase diameter .4mm
Verify with Fluorescien & Steepen Base Curve .10mm
Steep Base Curve
Center Thickness
Small Diameter
Flat Base Curve
Cause
Correction
Steepen Base Curve .10mm & increase diameter .4mm
Toric PC
Reduce diameter .4mm & steepen Base Curve .10mm
A/R Astigatism
Narrow aperture
Lens Position:
Down & In/Out
Oblique Position
LENS
Cause
Correction
Steepen Base Curve .10mm & increase diameter .4mm
Toric PC
Oblique astigmatism
Additional Reading Materials
VFL3 Fitting Procedure Guide
Base curve computation, Select Diameter, Power Computation Peripheral Curve Selection, Trouble shooting lens position cause and corrective action.
VFL3 Fit Evaluation Guide
Central Postition, High Position, Low Position, Nasal/Temporal Position, Lens Movement and Fluoroscein Dye Pattern Evaluation.
VFL3 Over-Refraction Guide
Over-refraction procedure and examples.
Parameter Change Effect
Parameters
Parameter Change Effect
Base Curve:
Diameter:
Optic Zone:
Peripheral Curve:
Blends:
Center Thickness:
Edge Thickness:
To Tighten Fit
Steeper
Larger
Larger
Steeper
Light
Thin
Thin
To Loosen Fit
Flatter
Smaller
Smaller
Flatter
Heavy
Thick
Thick
Over Refraction Evaluation
VFL 3 Over-Refraction Procedures:
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Allow at least 15 minutes for VFL 3 trial lens to equilibrate. Trial lenses must center well in order to achieve an accurate over-refraction.
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Over-refract with phoropter to determine best binocular distance correction.
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Transfer distance over-refraction to a trial frame and test the patient's distance and near vision, binocularly.
-
Add additional plus power to the trial frame, binocularly, in +0.25 increments to enhance near vision as needed. As each increment of plus is added, ask the patient to refer back to the distance chart. This will enable you to determine the maximum plus your patient will accept at distance.
-
It is important to work in +0.25 increments in order to achieve the best near vision without overplussing distance. The near / far balance is critical to the success of your patient. Most patients will accept more minus at distance and more plus at near than should be prescribed. Your objective is to find the balance that satisfies both distance and near. Caution - If the patient's vision is plussed to an unacceptable level in order to achieve acceptable vision at near, call consultation to discuss the additional add capabilities of the VFL 3 HD-AP.
-
Combine all add powers for each eye as follows:
OD OS
VFL 3 trial lens -3.00 -3.00
Distance OR -0.75 -1.00
Near OR +0.25 +0.50
Power to order -3.50 -3.50