TWO BASE CURVES FOR FIT AND COMFORT
PRODUCT SPOTLIGHT – UNITY BIOSYNC CONTACT LENSES WITH HYDRAMIST
By Linda Conlin, ABOC, NCLEC
Release Date: March 1, 2021
Expiration Date: April 1, 2022
Upon completion of this program, the participant should be able to:
- Define the elements for successful contact lens wear: comfort, wear time, eye health, vision and handling.
- Explain the importance of base curve selection in the contact lens fitting process.
- Describe how the two base curve options and design technology behind Unity BioSync contact lenses satisfy the criteria for successful contact lens wear.
To Earn Continuing Education Credit:
This course has been approved for one (1) hour of Ophthalmic Level II continuing education credit by the NCLE. Course Number: CTWJHI106-2
THIS COURSE IS SUPPORTED BY AN EDUCATIONAL GRANT FROM VSP
Currently, there are approximately 42 million contact lens wearers in the U.S., but nearly 7 million have dropped out. Studies have shown that less than optimal fit and lens dryness causing discomfort decreases wearing time and increases patient dissatisfaction with contact lenses. Learn about how the design and technology behind Unity BioSync® with HydraMist® daily disposable lenses in two base curves benefit patients with improved comfort, wear time, eye health, vision and handling.
WHAT DOES IT TAKE FOR SUCCESSFUL CONTACT LENS WEAR
The essential elements for successful contact lens wear are comfort, wear time, eye health, vision and handling. Lenses must feel good all day, they must maintain corneal health, provide good vision, and be easy to insert and remove. Let’s take a closer look at each of these factors.
COMFORT AND WEAR TIME
The key to contact lens comfort is to eliminate lens awareness, which is most often due to lens dryness. Natural tear film lubricates, smooths and protects the ocular surface. The closer a contact lens can mimic the ocular surface, the more comfortable it will be, and the healthier it will be for the eye. To understand this, we need to examine the tear film.
The tear film consists of three layers: an outer lipid or oily layer that prevents tear evaporation, a middle aqueous or watery layer that provides oxygen and nutrients to the underlying avascular corneal tissue, and an inner mucin or mucus layer that allows tear film to adhere to the eye. When a contact lens is placed on the eye, it disrupts the delicate balance of the tear layers. The contact lens keeps the mucin layer behind it and disrupts the lipid layer, allowing for evaporation of the aqueous layer. This results in lens dryness and subsequent discomfort. When lenses are dry and uncomfortable, patients can’t wear them all day. They become dissatisfied with lens performance and may discontinue lens wear altogether (Fig. 1).
Unity BioSync with HydraMist was developed in partnership with Tangible® Science, to enhance the wearing comfort of Unity BioSync’s silicone hydrogel material. HydraMist is a 90 percent water polymer that mimics the eye’s natural tear film. It is permanently bonded to the surface of the contact lens, effectively creating a mucin-like wetting surface on the underlying lens material and shielding it from the ocular surface and tear film. This proprietary moisture-retaining polymer coating stabilizes patients’ tear film and ensures consistent moisture to the eye during all-day wear (Fig. 2).
Edge design is another factor in contact lens comfort. Soft contact lenses cover the surface of the cornea and extend over the limbus (the border between the transparent cornea and opaque sclera) onto the sclera by approximately 1 mm. Studies have suggested that the interaction between the lens edge and the ocular surface at the periphery plays an important role in lens fitting. In general, silicone hydrogel lenses have four edge designs: round, semi-round, chisel and knife-edged. The different designs can result in different levels of conjunctival indentation on the sclera, affecting comfort, lens positioning, lens motion and overall fit.
A 2015 study published in Clinical Ophthalmology showed that chisel-edge and semi-round edge lenses produced the highest degrees of conjunctival indentation, while knife and round-edge designs induced the lowest amount. The unique design characteristics and manufacturing methods of Unity BioSync result in a smooth, welltapered, round-edge profile. This edge configuration enhances patient comfort while resting on the bulbar conjunctiva (the thin layer of tissue that covers the sclera) throughout the wearing period (Fig. 3).
Oxygen is critical to the health and survival of corneal cells, not to mention all cells in our bodies. The cornea gets its oxygen from the atmosphere. Forming a barrier of sorts, contact lenses can impede the flow of oxygen to the cornea, unless the lens material allows oxygen to pass through. When the cornea is deprived of oxygen, it affects corneal metabolism, a condition known as hypoxia. Corneal hypoxia can result in ocular surface inflammation, corneal swelling, microcysts, limbal hyperemia (filling of the blood vessels at the limbus), neovascularization (encroachment of blood vessels into the cornea) and changes in the composition of the tear film. The compromised cornea is then more susceptible to infection.
Unity BioSync lenses are made from olifilcon B, a silicone hydrogel material. The composition of the lens is 53 percent olifilcon B and 47 percent water. The olifilcon B material has a Dk/t (oxygen transmissibility) value of 150 and offers an increased level of oxygen transmittance throughout the day. In fact, it allows up to five times more oxygen to permeate through the contact lens and reach the cornea when compared to standard hydrogel contact lenses (Fig. 4).
What’s more, Unity BioSync includes a UV blocker. The UV transmission is less than 50 percent in the UVA range of 316 to 380 nm and less than 5 percent in the UVB range of 280 to 315 nm. (Note: UV-absorbing contact lenses are NOT substitutes for protective UV-absorbing eyewear such as UV-absorbing goggles or sunglasses because they do not completely cover the eye and surrounding area. Patients should continue to use UVabsorbing eyewear as directed.)
The clear reproducible optics Unity BioSync lenses provide result in excellent visual acuity for the patient. Plus, the HydraMist treatment keeps the lenses “wetter” on the eye longer, which equates to consistent acuity throughout the wearing time as well. HydraMist is deposit resistant, too. Lipid and protein deposits on contact lenses result in a foggy hydrophobic surface. This can induce an inflammatory response in the eye, resulting in irritation. Limiting deposits on contact lenses promotes tear film stability. Lenses that maintain wettability and resist protein and lipid deposits are likely to remain moist and comfortable on the eye while providing clear, crisp vision.
The modulus of a material describes how well it holds its shape. Higher modulus in contact lenses is associated with better handling, ease in establishing whether the lens is inside out and application and removal. However, a soft contact lens must also conform to the shape of the cornea and sclera during wear. A lack of good conformity, as can occur in lenses with high modulus, may result in edge fluting (or edge standoff). Fluting is usually associated with immediate and consistent awareness of the lens on the eye and other complications, including mechanical effects associated with lens wear by some patients, such as contact lens papillary conjunctivitis (CLPC), superior epithelial arcuate lesions (SEALs), limbal epithelial hypertrophy (LEH), generation of mucin balls and resistance to full draping on the anterior ocular segment. In general, contact lens designs should achieve a good balance between oxygen supply, wearing comfort and handling by finding the right mix of modulus, silicone and water content, as well as surface treatment. Unity BioSync lenses check all those boxes and have a visibility tint to make handling even easier.
ONE SIZE DOESN’T FIT ALL
As we know from so many other products, one size just doesn’t fit all. This is especially true with contact lenses. A study published in the Journal of Current Ophthalmology in 2019 found that of more than 2,600 subjects, mean flat keratometry readings were 42.98D, and mean steep keratometry readings were 43.99D, a difference of a full diopter. Considering lenses of the same diameter, would one base curve provide the same fit and comfort to both? Maybe not.
A successful contact lens fit provides adequate distribution of the contact lens weight over the entire corneal surface, leading to proper lens position, good centration and enough movement to have optimal tear flow, all of which produce minimal mechanical effect between the eye and the contact lens. If the contact lens shape does not fit properly on the ocular surface, it will produce different pressure points that could result in complications.
Lenses that are poorly fitted may negatively impact the ocular surface. A lens that does not cover the cornea completely may result in irritation from its edge. Lenses fitted too loosely have excessive movement, which causes discomfort and visual fluctuations, particularly with blinking. The normal blink rate for healthy humans may be as high as 1,000 to 1,200 times an hour. Thus, it’s important that the contact lens does not move more than 0.50 mm on blinking or cause any irritation with the palpebral conjunctiva (the clear membrane that coats the inside of the eyelids). Tightfitting lenses, although initially appearing to fit more comfortably, when excessively tight reduce tear exchange, leading to a buildup and trapping of metabolic waste and toxins under the lens. For these reasons, the process of contact lens fitting and the assessment of the contact lens fit are both vital to healthy contact lens wear.
When considering base curve, there is a mathematical correlation between base curve and overall diameter to a sagittal value. Sagittal value or SAG is the height or depth of a segment of a circle or sphere. The value is used to describe the distance between the ocular surface and the backside of the contact lens. The relationship between the sagittal depth of the lens and the sagittal height of the anterior segment of the eye over the lens diameter largely determines the fit of the lens. Theoretically, if the lens sag is greater than the ocular sag, the lens will fit steeply and vice versa. In general, the sagittal height of the Unity BioSync contact lens in an 8.8 mm base curve is greater than the base curve/diameter relationship mathematically would suggest. But there are other variables that play a role as well. These are optic zone size, peripheral zone configuration and modulus. Considering those factors, the Unity BioSync 8.5 mm is the base curve that is mostly indicated for corneas of 45.00D and greater, but for smaller corneas with a normal keratometry reading, it may be an optimum fit as well.
Prior to the launch of the 8.5mm base curve in 2020, two sites were asked to evaluate a series of contact lens wearers by refitting them from their usual lens into Unity BioSync. While the subject’s response was measured by numerous criteria such as vision, centration, movement and wearing comfort, the main goal was to determine which of two base curves (8.8 mm or 8.5 mm) was ultimately chosen to provide the best fit for each subject. Forty-two subjects (84 eyes) were evaluated. Of these, almost 70 percent were fit in the 8.8 mm base curve with the remaining 30 percent in the 8.5 mm. Most evaluated patients (73 percent) fell in the category of medium corneal curvature and could be an ideal fit for either base curve. Only about 5 percent of subjects showed K-readings in the flat range (less than 42.00) while 23 percent showed a steeper cornea (greater than 45.00). When analyzing the base curve to K-reading relationship of this evaluation, those with K-readings less than 42.00D were fit mostly in the 8.8 mm base curve (75 percent). Of those with Ks between 42.00D to 45.00D, 72 percent were fit in the 8.8 mm, while even in the steeper range of greater than 45.00D, more than half the eyes (58 percent) utilized the 8.8 mm as well. The results show that there is more to the lens fit than just the base curve, and your expertise will guide you in choosing the right lens for your patient. It also demonstrates the benefits of having a product that offers two base curves, allowing you to find the optimal fit for your patients.
While Unity BioSync lenses currently provide spherical correction, the design will easily correct up to 0.75D of refractive cylinder, and even more when using spherical equivalent calculations. Lenses are in development for presbyopic and astigmatic correction so you can offer these lenses to a broad spectrum of your patient base. (Note: The spherical equivalent is calculated by adding the sum of the sphere power with half of the cylinder power. For example, with a spectacle correction of -2.00 -1.00 x 90, the spherical equivalent = -2.00D + ½(-1.00D) = -2.00D + (-0.50D) = -2.50D spherical equivalent.) What’s more, Unity BioSync provides the opportunity to upgrade two-week and monthly wearers to a healthier way to wear contact lenses. Studies have shown that daily disposable contact lenses achieve an 88 percent compliance rate with patients, while the compliance rate is only around 72 percent with monthly and even less with two-week lenses (48 percent). When patients dispose of their lenses every day, they don’t have to keep track of a replacement date and are less likely to wait until the lenses feel uncomfortable before replacing them.
A lens that fits well will provide full corneal coverage, have good centration, a lens lag with blink of 0.1 mm to 0.5 mm movement after blink, free lens movement during the push-up test, and satisfactory vision and comfort for the patient. Let’s look at the fitting process needed to accomplish these objectives.
Although there are several factors to consider in contact lens fitting, keratometry readings provide a reference point for the initial lens selection and evaluation. For Unity BioSync, the manufacturer suggests using the 8.8 mm base curve for corneas flatter than 42.00 average readings. When average Ks are between 42.00D to 45.00D, either the 8.8 mm or 8.5 mm base curve may work well. However, it is good practice to use the 8.8 mm diagnostic lens as the starting point and move to an 8.5 mm if the 8.8 mm doesn’t provide the desired fit. For average Ks over 45.00D, select the 8.5 mm diagnostic lens for initial evaluation (Fig. 5).
The diagnostic lens should be allowed to settle for 10 to 20 minutes before beginning the evaluation process. First, look at the overall corneal coverage to ensure the lens overlaps the cornea by about 1.0 mm all the way around. Next, evaluate centration. Although it’s not unusual for soft lenses to follow the typical corneal-scleral shape (that is, steeper centrally and flatter toward the periphery) and decenter slightly inferior temporally (low and toward the outside), the Unity BioSync design usually centers quite well.
During the slit lamp examination, watch for normal blinking and lens movement directly following each blink. This is best done without asking the patient to force a blink, but instead let it occur naturally. Ideally, there should be 0.1 mm to 0.5 mm movement after the blink, accompanied by subtle lens lag during the patient’s upward gaze. Proper lens movement also can be evaluated using the “push up test.” Gently push up on the lower lid to decenter the lens slightly upward, then release the lid. The lens should recenter smoothly. If the lens resists decentration, it is too tight, and a flatter base curve is needed. If the lens movement is excessive or it doesn’t recenter smoothly, it is too loose, and a steeper base curve is needed (Fig. 6). (Note: The lenses pictured were dipped in lissamine dye prior to lens insertion on test subjects for demonstration purposes only. It’s easier to visualize soft lens performance in a document or picture in this manner. Unity BioSync lenses are not this color. Also, it is not advised to use the lissamine dye in this manner in direct patient care.) A tight or steep lens may result in insufficient or no movement during the blink cycle in primary or upward gaze. The patient’s vision could also be impacted between blinks. If this occurs with the 8.5 mm base curve, consider switching to 8.8 mm for a flatter fit and to decrease signs and symptoms of problems from a lens that is too tight. A loose or flat fit may be uncomfortable, show increased decentration and sometimes result in excessive movement during blinking and upward gaze. In the extreme, there may be edge standoff. If this is noticed with the 8.8 mm base curve, consider an 8.5 mm lens instead. Larger corneas may need the flatter 8.8 mm base curve, while smaller corneas may achieve a better fitting relationship with the steeper 8.5 mm base curve. Due to subtle differences in individual eyes, a two-base curve system is helpful in achieving the best fitting relationship possible.
Follow-up examinations, as recommended by the eyecare practitioner, are necessary to ensure continued successful contact lens wear with Unity BioSync and any contact lens prescribed. Here are some tips for evaluating the results on subsequent visits.
• Prior to a follow-up examination, the contact lenses should be worn for at least four continuous hours, and the patient should be asked to identify any problems that might be occurring related to contact lens wear.
• With lenses in place, evaluate the lens performance to assure that the fitting criteria have been achieved.
• Remove the lens and conduct a thorough biomicroscopy examination.
Signs and symptoms to address include:
• Discomfort on blinking—may indicate a loose lens.
• Variable vision after blinking—may indicate a loose lens.
• Edge fluting or buckling—may indicate a loose lens.
• Lens movement more than .50 mm—lens is too loose.
• Poor lens centration—may indicate a loose lens.
• Conjunctival redness—may indicate a tight lens.
• Low grade inflammation—may indicate a tight lens.
• Vision improves immediately post blink— may indicate a tight lens.
• Conjunctival indentation—may indicate a tight lens.
• Lens movement less than .25 mm—lens is too tight.
The Unity BioSync with HydraMist spherical lens design addresses key elements to successful contact lens wear. Its two base curves provide fitting options for a broad group of patients. The high Dk/t in olifilcon B silicone hydrogel material offers high oxygen transmissibility and in combination with HydraMist technology, is very comfortable for patients to wear all day. Up to five times more oxygen permeates through the contact lens to reach the cornea when compared to stan dard hydrogel contact lenses, and HydraMist technology mimics natural tear film, both key elements for healthy and comfortable contact lens wear, all-day every day.
Single use daily disposable lenses provide convenient and deposit-free wear—every day. Studies have shown that patients have higher compliance rates with daily disposable lenses than with other modalities. This provides the opportunity to upgrade twoweek and monthly wearers to a healthier way to wear contact lenses.
The light blue visibility tint makes the lens easy to see, and the modulus allows for the lens to rest on the finger in a form easy to apply to the eye. There is also less confusion for patients in determining whether a lens is inverted before insertion. Unity BioSync has the right mix of modulus, silicone and water content as well as surface treatment for better handling and comfort.
The high-quality optics resulting from the proprietary manufacturing methods provide excellent visual acuity. And the HydraMist treatment keeps the lenses “wetter” on the eye longer, which equates to consistent acuity throughout the wearing time as well. Patients will have good vision and comfort all day.
It is easy to see Unity BioSync lenses as a great choice for new or existing contact lens patients. With all-day comfort, clear vision, convenience and fitting choices, your patients get what they expect from contact lenses, and you can take pride in guiding them to a healthy choice for their eyes.