The process of obtaining and evaluating a Biofinity toric trial is a sophisticated clinical procedure designed to manage the complexities of astigmatism through advanced silicone hydrogel technology. For the UK consumer and the prescribing practitioner, the trial phase is the most critical juncture in the fitting process, as it determines the stability, comfort, and visual acuity of the lens on the individual eye. Biofinity toric and Biofinity XR toric lenses are engineered as monthly replacement options specifically for patients suffering from astigmatism, which includes those with myopia (short-sightedness) or hyperopia (long-sightedness) combined with astigmatic corneal curvature. The primary objective of a trial is to ensure that the Optimised Toric Lens Geometry™ functions correctly by minimising lens rotation, which is the most common cause of blurred vision in toric lenses. By utilising a trial, the wearer can experience the Aquaform® Technology, which allows the lens to remain naturally wettable without the need for synthetic surface treatments or coatings, ensuring a high level of oxygen permeability for the long-term health of the cornea.
Clinical Trial Fitting Methodology
The fitting of a Biofinity toric trial lens follows a rigid, step-by-step clinical protocol to ensure that the final prescription is accurate and the lens remains stable during normal ocular activities.
Step 1: Initial Refraction and Selection The process begins with a fresh refraction to establish the current spectacle power. The practitioner must then convert these spectacle values into contact lens power using a specific conversion table. For the initial trial, the lens axis selected should be the one closest to the spectacle axis. Biofinity toric lenses are available in round-the-clock axes, provided in 10-degree increments, allowing for precise alignment with the patient's astigmatism.
Step 2: Insertion and Stabilisation Once the trial lens is inserted, a mandatory waiting period of 10 minutes is required. This interval is essential because the lens needs time to settle on the eye, allowing the Optimised Toric Lens Geometry™ to find its natural orientation and the tear film to stabilise. Evaluating visual acuity immediately upon insertion would lead to inaccurate results.
Step 3: Physical Fit Evaluation After the stabilisation period, the practitioner evaluates three specific criteria: - Corneal coverage and centration: Ensuring the lens covers the cornea adequately and remains centred. - Blink movement: Checking how the lens moves during blinking in both the primary gaze and the upgaze position to ensure stability. - Toric marking and rotation: Observing the lens markings to determine the exact direction and angle of any rotation that has occurred.
Step 4: Visual Acuity and Refinement The final step involves performing a spherical over refraction. If the visual acuity improves during this process, the practitioner may select a new trial lens with adjusted sphere power or proceed to dispense the lenses with the updated power. It is critical to note that if significant lens rotation is present, simply adding plus or minus sphere power will not correct the vision; instead, axis compensation is required.
Axis Compensation Systems
When a Biofinity toric trial lens rotates on the eye, the axis of the correction no longer aligns with the axis of the astigmatism. To correct this, practitioners use specific compensation methods to determine the final prescription.
The LARS Method LARS stands for Left Add, Right Subtract. This is a directional adjustment based on the direction of the lens rotation to ensure the correction is shifted to the correct orientation.
The CAAS Method CAAS stands for Clockwise Add, Anti-clockwise Subtract. This method provides a geometric approach to adjusting the axis based on the degree of rotation observed via the toric markings.
Material Science and Technical Specifications
The Biofinity toric trial allows the user to experience the specific material properties of Comfilcon A, a silicone hydrogel designed for maximum breathability and comfort.
Technical Data Table
| Attribute | Specification |
|---|---|
| Material | Comfilcon A (Silicone Hydrogel) |
| Base Curve (BC) | 8.7mm |
| Diameter (DIA) | 14.5mm |
| Water Content | 48% |
| Oxygen Permeability (DK) | 128 |
| Gas Flow | Very High (DK > 99) |
| Modulus | 0.75 |
| UV Protection | No |
| Light Tint | Yes |
The high DK value of 128 ensures that the eye receives sufficient oxygen, which is vital for maintaining clear, white, and healthy eyes. The naturally wettable material removes the need for coatings, reducing the risk of lens deposits and increasing the overall comfort duration for the wearer.
Prescription Range and Availability
Biofinity offers one of the widest silicone hydrogel prescription ranges in the industry, claiming to provide correction for 99.9% of astigmatic patients. This range is split between the standard Biofinity toric and the Biofinity XR toric for extended ranges.
Standard Biofinity Toric Power Range
- Sphere: -6.00 to plano (0.25D steps)
- Sphere: +0.25 to +6.00DS (0.25D steps)
- Sphere: +6.50 to +8.00DS (0.50D steps)
- Sphere: +8.50 to +20.00DS (0.50D steps)
- Cylinder: -0.75 / -1.25 / -1.75 / -2.25
- Axis: 10° to 180° (10° steps)
Biofinity XR Toric Extended Range
The XR range is specifically designed for patients with higher prescriptions, offering a vast array of combinations including 32,796 toric prescription options.
- Cylinder -2.75: Sphere +8.00 to -10.00 (0.50 steps above +/- 6.00), Axis 10° to 180° (10° steps).
- Cylinder -2.75: Sphere Plano to -6.00 (0.50 steps only), Axis 5° and 175°.
- Cylinder -3.25: Sphere Plano to -10.00 (0.50 steps above -6.00), Axis 10° to 180° (10° steps).
- Cylinder -3.25: Sphere Plano to -6.00 (0.50 steps only), Axis 5° and 175°.
- Cylinder -3.75: Sphere Plano to -10.00 (0.50 steps above -6.00), Axis 10° to 180° (10° steps).
Wearer Benefits and Experience
The trial period is designed to demonstrate several key benefits that differentiate the Biofinity range from other monthly toric lenses.
Visual Stability The Optimised Toric Lens Geometry™ is the core engine of the lens. By reducing the amount of rotation that occurs when a user blinks or moves their head, the lens provides consistent visual acuity. For the astigmatic patient, this means the vision does not "blur" or "shift" during active movements.
Comfort and Breathability Aquaform® Technology ensures that the lens remains hydrated. Because the material is naturally wettable, the user experiences all-day comfort. The high oxygen permeability prevents the hypoxia often associated with lower-quality lenses, ensuring the sclera and cornea remain healthy.
Flexible Wearing Schedule Biofinity toric lenses offer a flexible wearing regime. While they are primarily monthly replacement lenses, they are approved for extended wear, which includes overnight wear for up to 6 nights and 7 days. This flexibility is a significant advantage for users who find daily insertion and removal cumbersome.
Comparative Ecosystem
The technology found in the Biofinity toric trial is not limited to monthly lenses. For users who prefer a different replacement cycle, the same technology and design are available in the MyDay® toric, which is a daily disposable version. This allows patients to move between monthly and daily options without sacrificing the stability and comfort provided by the Optimised Toric Lens Geometry™.
Environmental and Logistics Integration
CooperVision has integrated sustainability into the distribution of the Biofinity family. The company utilises a plastic neutrality program through the Plastic Bank. For every Biofinity order, which includes the sphere, Energys, toric, multifocal, and XR variants, CooperVision purchases credits equal to the weight of the plastic used in the packaging. This means that for every kilogram of plastic used in a trial or full supply, an equivalent amount of plastic is collected and converted from waterways.
Analysis of the Fitting Journey
The transition from a spectacle prescription to a Biofinity toric lens is a process of iterative refinement. The trial is not merely a test of "if it fits," but a calibration of the lens axis relative to the patient's ocular anatomy.
The critical nature of the 10-minute settling period cannot be overstated. In many failed trials, the lens is evaluated too quickly, leading to incorrect axis compensation calculations via the LARS or CAAS methods. When the lens rotates, it is not a failure of the lens but a requirement for the practitioner to adjust the prescribed axis to account for that specific eye's rotation patterns.
Furthermore, the breadth of the XR range removes the "prescription ceiling" often encountered by patients with high cylinders or spheres. By offering options up to -3.75 cylinder and +20.00 sphere, the Biofinity range ensures that almost no patient is left without a viable soft lens option.
The synergy between the 8.7mm base curve and the 14.5mm diameter provides a stable platform for the toric geometry to engage with the lower lid and cornea. This physical stability, combined with the Comfilcon A material's modulus of 0.75, results in a lens that is flexible enough for comfort but rigid enough to maintain its orientation.
Ultimately, the Biofinity toric trial serves as the verification phase for the promise of "99.9% correction." It transforms a theoretical prescription into a tangible visual experience, ensuring that the patient achieves the highest possible visual acuity through a scientifically managed fitting process.