4F Custom RGP – Cantor Barnard

4F Custom RGP by Cantor Barnard is a custom-made rigid gas permeable contact lens manufactured according to the corneal measurements and prescription of each eye.

The design combines a:

4-Curve Design

with an:

Aspheric Back Surface / Periphery

providing a smooth transition from the central optical zone toward the lens periphery and supporting an appropriate fit when the correct parameters are selected by an eye care professional.

Cantor Barnard classifies 4F as a high-quality custom RGP lens intended for:

Daily Wear

Delivery Time

The lenses are supplied within a maximum period of:

30 to 60 days

from the date the order is confirmed.

Custom Optical Design

The 4F design offers an officially published power range of:

-30.00D to +30.00D

and can be manufactured in several different RGP materials.

This allows the eye care professional to select the most appropriate material according to:

• Oxygen permeability requirements
• Lens stability
• Wettability
• Prescription
• Lens design
• Wearing requirements

Current material options include:

• Optimum Classic
• Optimum Comfort
• Optimum Extra
• Optimum Extreme
• Optimum Infinite

The lens is not supplied as a standard one-size-fits-all product.

The following parameters must be professionally determined:

• Base Curve
• Diameter
• Power
• Material
• Any required Toric modifications

For a product page, it is most appropriately presented as:

Custom Made / Made to Order

with prescription review by an eye care professional before manufacturing.

Key Features

• 4-Curve Design
• Aspheric Periphery
• Custom-made according to the measurements and prescription of each eye
• Published power range from -30.00D to +30.00D
• Multiple Optimum material options
• Different oxygen permeability levels
• Specialized Toric options
• Daily Wear
• Stable RGP optical performance
• Professionally fitted
• Manufactured in the United Kingdom

Suitable Applications

The 4F lens is primarily intended to correct refractive errors using a customized corneal RGP lens.

Suitable corrections include:

• Myopia
• Hyperopia
• Astigmatism

It may be particularly useful when the patient requires:

• Custom Base Curves
• Custom Diameters
• Higher or unusual powers
• Parameters unavailable in standard stock lenses
• Specialized Toric modifications

4F should not primarily be presented as a dedicated Keratoconus lens.

Cantor Barnard offers other designs specifically intended for irregular corneas and Keratoconus, including Nissel KII.

Basic Product Information

4F Design Concept

The principal feature of the design is the combination of:

Four Curves

with an:

Aspheric Back Surface

The objective is to provide a smooth peripheral transition and a balanced relationship between the lens and cornea.

Historical Oxyflex 4F literature describes the design as aiming to provide:

Balanced Periphery

with:

Optimum Edge Lift

across the fitting range.

The current version is described as:

4-Curve with Aspheric Periphery

Design Specifications

Current Base Curve Range

The current official booklet lists the following Base Curves:

7.05 – 7.12 – 7.20 – 7.27 – 7.35 – 7.42 – 7.50 – 7.57 – 7.65 – 7.72 – 7.80 – 7.87 – 7.95 – 8.02 – 8.10 – 8.17 – 8.25 – 8.32 – 8.40 – 8.47 mm

Additional values may be available on request.

Diameter

Current published range:

8.60–10.60 mm

in:

0.10 mm steps

Older literature listed specific Diameters such as:

8.60 / 9.00 / 9.40 / 9.80 / 10.20 / 10.60 mm

For a current product listing, the published range of:

8.60–10.60 mm in 0.10 mm steps

is the more appropriate reference.

Power Range

Current published range:

-30.00D to +30.00D

Power steps:

0.25D

Higher powers:

May be available on request

Older 4F literature included ranges up to approximately:

±40.00D

but this should not be presented as a standard current option unless confirmed by Cantor Barnard for the specific order.

Current Material Options

The current January 2026 booklet lists five Optimum materials:

These materials provide a broad range of oxygen permeability values.

Optimum Classic

Dk 26

A relatively lower-Dk material primarily suited to conventional daily-wear corneal GP lenses.

Optimum Comfort

Dk 65

A mid-Dk option appropriate for daily-wear corneal lenses.

Optimum Extra

Dk 100

Provides higher oxygen permeability together with good wettability.

Optimum Extreme

Dk 125

A high oxygen-permeability material suitable for a broad range of GP designs.

Optimum Infinite

Dk 180

A Hyper-Dk material offering very high oxygen permeability together with good resistance to flexure and scratching.

Material selection should be made by the eye care professional according to:

• Lens thickness
• Corneal oxygen requirements
• Wearing hours
• Prescription
• Lens design
• Clinical needs

Handling Tints

Cantor Barnard lists:

• Blue
• Clear
• Green
• Grey

Actual tint availability depends on the material selected.

Recommended wording:

Handling Tint: According to color availability for the selected material.

Refractive Applications

The official 4F information lists correction for:

The design is primarily a customized corneal RGP for general refractive correction.

Toric Options

Cantor Barnard lists several specialized Toric options:

• Toric Flange
• Back Surface Toric
• Front Surface Toric
• Bi-Toric

These should be presented as:

Professional fitting options

rather than customer-selected cosmetic or standard retail options.

When May Back Surface Toric Be Required?

Cantor Barnard fitting guidance states that a:

Back Surface Toric

may be required when:

• Corneal astigmatism exceeds approximately 2.50D
• The difference between K readings is approximately 0.50 mm or more

When May Front Surface Toric Be Required?

When the cornea is relatively spherical but refractive astigmatism exceeds approximately:

-1.25 DC

a:

Front Surface Toric

may be considered.

Initial Base Curve Selection

The Cantor Barnard fitting guide provides the following starting points:

These values are professional fitting starting points and not final prescriptions.

Power Adjustment When Changing Base Curve

According to the Cantor Barnard guide:

If the selected Base Curve is:

0.05 mm steeper than Flattest K

apply approximately:

Add -0.25D

If the selected Base Curve is:

0.05 mm flatter

apply approximately:

Add +0.25D

Cantor Barnard also recommends considering:

Back Vertex Distance – BVD

adjustment when spectacle power exceeds approximately:

±4.00D

Diameter Selection

The initial fitting guideline is:

Total Diameter ≈ HVID − 2.00 mm

In other words, the lens Diameter is initially selected approximately:

2 mm smaller than HVID

and then adjusted according to the actual on-eye fitting pattern.

Good / Alignment Fit

A good fitting relationship should generally show:

• Good centration
• Lens remains within the corneal margin during different directions of gaze
• Smooth vertical movement of approximately 1–1.5 mm
• Fluorescein pattern showing alignment or only very slight central clearance
• Edge Clearance of approximately 0.40–0.60 mm

Flat Fit

A lens that is too flat may show:

• Excessive and rapid movement
• Poor stability
• Poor centration
• Wide Edge Clearance
• Discomfort
• Variable vision

The main recommended adjustment is:

Select a steeper BOZR

Additional adjustments may include:

• Increasing Diameter
• Increasing BOZD

Steep Fit

A lens that is too steep may show:

• Very little movement
• Excessive central positioning
• Central Pooling
• Narrow fluorescein band at the edge

The main adjustment is:

Select a flatter BOZR

Additional adjustments may include:

• Reducing Diameter
• Reducing BOZD

Replacement Schedule

Cantor Barnard classifies 4F as:

Daily Wear

with a maximum replacement period of:

12 months

The actual replacement interval should be determined by the eye care professional according to:

• Lens condition
• Surface quality
• Prescription changes
• Deposits
• Wearing pattern
• Ocular health

Wearing Instructions

The Optimum materials used with 4F are intended for:

Daily Wear

The lenses should be:

Removed before sleeping

unless specific professional and manufacturer instructions state otherwise.

The wearing schedule should be determined by the eye care professional and may be increased gradually according to ocular tolerance.

Lens Care Instructions

4F lenses should be cleaned and disinfected using a care system appropriate for:

RGP Contact Lenses

and compatible with the selected lens material.

Recommended care includes:

• Wash hands thoroughly before handling the lens
• Rinse and dry hands completely
• Use only recommended RGP cleaning, disinfecting, and storage solutions
• Use fresh, sterile, unexpired solution every time
• Do not use saliva to wet or clean the lens
• Do not use liquids not intended for contact lens care
• Store the lens fully immersed in the recommended storage solution when not being worn
• Follow the recommended lens-case cleaning instructions
• Replace the lens case regularly
• Avoid touching the lens surface with fingernails or instruments that may produce fine scratches

When Should Lens Wear Be Stopped?

Remove the lens and contact an eye care professional if you experience:

• A lens that becomes immobile on the eye
• Redness
• Eye pain
• Burning
• Itching
• Discharge
• Increased tearing
• Blurred vision
• Reduced visual acuity
• Light sensitivity

Important Warnings

4F is a custom medical rigid gas permeable contact lens manufactured according to the prescription and ocular measurements of each eye. Its parameters and fitting must be determined by an eye care professional.

The lens is intended for:

Daily Wear

and should not be worn during sleep.

The material, Base Curve, Diameter, power, and any Toric modification should be selected according to clinical assessment and manufacturing availability.

Remove the lens and consult an eye care professional if pain, redness, increased tearing, or changes in vision occur.