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HomemieyecareToric Lens Design: Meeting Patient Needs

Toric Lens Design: Meeting Patient Needs


According to NSIGHT Study results, what patients most desire is good vision yet what they are not entirely satisfied with is their current vision correction. High rates of vision-related symptoms experienced from wearing both contact lenses and spectacles suggests patients would welcome the stable, consistent and comfortable vision that can be achieved with advanced options, such as toric contact lenses.[/vc_column_text][/vc_column]

Throughout the history of contact lens design, the challenge of meeting the needs of astigmatic individuals has been significant. It is important to continue to strive to meet those needs when we consider the population that requires this correction. It has been reported that approximately 37 per cent to 45 per cent of adults have 0.75D or more of astigmatism.1-3 With almost half of the population of contact lens wearers having significant astigmatism2, the contact lens industry as a whole must continue to support the needs of this large group of patients.

Manufacturers need to have access to new and improved contact lens materials to compete effectively in the contact lens market. Optics of contact lenses, however, play a crucial role in successfully fitting patients. Insights from patients are also imperative in designing lenses that meet their needs and expectations. During the past five or six years it seems as though much emphasis has been placed on enhancing the comfort of lenses, although dropout rates have remained stable throughout this time period.4,5 This leads to the question: What else may be causing patients to stop using their contact lenses?

Patients visit their eye care practitioner when they are in need of new or updated vision correction. But does the solution offered, which reflects eye exam results, meet the full range of vision needs of the patient, including those pertaining to lifestyle? Are all options that might improve patient satisfaction – including, possibly, specialty contact lenses – receiving adequate consideration?

Vision was the highest-ranked product feature category among respondents surveyed…

NSIGHT Study

The NSIGHT (Needs, Symptoms, Incidence, Global Eye Health Trends) Study surveyed 3,800 vision-corrected patients to evaluate self-reported experiences, attitudes, and preferences.6 Patients included in the survey ranged in age from 15 to 65 years and were drawn from three global regions (United States, Europe, and Asia) that included seven countries (United States, United Kingdom, France, Italy, China, Korea, and Japan). The study reported two main outcomes: patients’ needs in relation to the selection of eye care products and the incidence of vision- and eye-related symptoms.6,7

Figure 1. In the NSIGHT Study, potentially beneficial product features related to vision consistently ranked as most compelling to patients.

Figure 2. Thickness profiles of a lens with Auto Align Design for stabilisation (a) and a lens with traditional prism ballasting for stabilisation (b), where the red colour indicates the thickest portions of the lens and the blue colour represents the thinnest portions of the lens.


To assess their preferences when selecting eye care products, respondents reviewed 40 features of eye care products in multiple groupings of six. For each group, they chose one feature as the most compelling and one as the least compelling. These rankings were analysed to produce a utility index score for each of the 40 features, which were then stratified into eight categories. Vision was the highest-ranked product feature category among respondents in all three of the global regions surveyed (Figure 1) and for contact lens and spectacle wearers.6

In addition to patients’ preferences regarding products, the NSIGHT Study also evaluated the incidence, management strategy, and overall satisfaction with available treatments for symptoms. With respect to vision, three symptoms in the survey – glare, halo, and blurry/hazy vision – stood out to researchers because these symptoms can be controlled with the design of contact lenses, specifically aspheric optics.

In the NSIGHT Study, glare and halo were experienced by 46 per cent and 39 per cent, respectively, of all contact lens-corrected patients.7 When asked under what conditions the symptoms were experienced, driving, bright lights, sunlight, headlights, and being in the dark or nighttime viewing were commonly reported. Blurry/hazy vision was reported by 39 per cent of patients overall, with higher rates reported by those with astigmatism (47 per cent). Little difference was seen between modes of correction. About 60 per cent of patients overall experienced blurry/hazy vision at least three times a week, with rates slightly higher among astigmats, and about 90 per cent of all patients who experienced this symptom found it bothersome.

Figure 3. Images comparing the thinner, rounded edge design of the Auto Align DesignT lens to the Quick Alignment System lens. Horizontal cross-section of -3.00D -1.25 x 180 lenses obtained using a Nikon Video Microscope with 20x magnification.



Figure 4. Images depicting the edges of commercially available Silicone Hydrogel Toric contact lenses: Horizontal cross-section of -3.00D -1.25 x 180 lenses obtained using a Nikon Video Microscope with 20x magnification.


As part of its comprehensive survey, the NSIGHT study also sought to identify unmet or insufficiently addressed needs among vision-corrected patients by examining the prevalence of vision disorders and treatments, patient satisfaction with their vision correction, and the incidence and bothersomeness of eye-related symptoms relating to inadequate correction. Both contact lenses and spectacles were used to meet patients’ vision correction needs, but there was a wide variance in their usage across different self-reported disorders. At least 70 per cent of all patients used spectacles as their main source of vision correction. Globally, across different types of vision problems, at least one-third of spectacle-wearing patients reported less-than-complete satisfaction with the spectacles they wear most often, as judged by a score of seven or less on a scale of one (very dissatisfied) to 10 (very satisfied). Satisfaction was lowest in Asia, across vision disorders.

In a separate survey of 201 astigmatic contact lens wearers, the symptoms most often cited while wearing current toric lenses included regularly or occasionally experiencing blurry/hazy vision, fluctuating vision, and distorted vision.8 Forty seven per cent of subjects reported experiencing blurry or hazy vision, 37 per cent reported fluctuating vision, and 32 per cent reported distorted vision. Additionally, 32 per cent of toric patients reported experiencing glare and halos in low-light conditions. Product benefits of toric lenses (in the categories of vision, comfort, health, and convenience) were presented to patients randomly in successive groups of four for ranking. The benefit of highest relative importance for a toric soft contact lens was that it should ‘deliver consistently sharp vision all day’.

Figure 5. A lens with spherical aberration has different focal points for the light rays passing through the center and the periphery of the lens.


(A)


(B)

Figure 6: Illustration of finite element analysis model of a non-conformed contact lens on the cornea (A) and a contact lens conformed to the cornea (B).


Such findings point to unmet needs that could, in the case of astigmatic spectacle wearers, potentially be addressed by consideration of properly fitted toric contact lenses. The dissatisfaction among astigmatic contact lens wearers could similarly reflect a need for more appropriately selected and fitted lenses. While contact lenses were the main source of vision correction in a minority of patients, at least 80 per cent of contact lens wearers, including those with astigmatism, would be bothered by losing access to their contact lenses regardless of region, age group, or gender.

Attributes and performance of current toric lenses may limit the ability of patients to achieve consistently crisp, clear vision throughout the day. Patients are looking for contact lenses that offer uncompromised vision and stability without compromising comfort.

Figure 7: Lenses with High Definition Optics are designed to reduce the positive spherical aberration that is naturally occurring in the human eye as well as reduce the spherical aberration induced by the contact lens on-eye to bring all of the light rays to the same focal point.

Lens Stability: Auto-Align Design
The stability of a toric lens is governed by several forces that can be divided into two groups: static and dynamic. Static forces include surface tension of the tears, gravity, conformity of the lens, and lid pressure at the top and/or bottom of the lens. Dynamic forces include upper and lower eyelid movement and eye movement. To better understand how lenses behave on-eye, several experiments were undertaken to understand blinking dynamics, one of the main drivers of instability.

Blinking is essential to maintenance of the ocular surface and occurs at a speed that is almost imperceptible. The main muscle drivers of the blink are the horizontally aligned obicularis oculi and the more vertically aligned, levator palpaebra and Muler’s muscles.

To capture the motion of these muscles, a high-speed camera, capable of recording 300 frames per second was employed. The results showed that from initiation to completion of the natural blink, only one tenth of a second passes. In that time the upper lid has traveled approximately 7.5mm down and 4.8mm nasal. Interestingly, the lower lid has limited vertical motion, leaving the upper lid to
be almost entirely responsible for rewetting the ocular surface through the blink mechanics.

Understanding these dynamics is beneficial when designing a lens that can work with the dynamic range of the eyelids.

To optimise lens stabilisation, blink dynamics should be taken into account. When the eyelids close during a complete blink, there is a slight downward displacement of the lens and the lids typically meet at a point 1-2mm from the base of the lens. For a lens to effectively leverage these blink dynamics and maintain stable orientation, the toric stabilising ballast should be designed
with this in mind.

Various innovative techniques have been employed to create a stable contact lens including truncation, dual slab-off, peri ballast and prism ballast, to name a few, and there are multiple designs currently commercialised which are founded on these basic geometries. By positioning the maximum ballast thickness low on the lens, the design can leverage the full motion of the upper lid while gaining support from the lower lid. Understanding eyelid movement during the blink and
lens movement associated with eye and eyelid movement helped guide the development of the Auto Align Design stabilisation method that allows the lens to achieve stability and orientation while providing consistently crisp, clear vision throughout the day.

Sophisticated lens design software and innovative manufacturing techniques were used in the development of the Auto Align Design to develop a lens that uses the best aspects of prism and peri ballasting to create a hybrid ballasting system. The design provides excellent stability for consistent vision, with repeatable orientation even with the blink and eye movement. Manufacturing sophistication has also come of age and is carefully sculpting the contours of these lenses to blend with and work with the eye. Larger diameters are also used to improve centration and offer more area to spread out the ballast design to reduce the maximum thickness of the lens (Figure 2). This helps create a more comfortable wearing experience, while maintaining a large optic zone that
helps to reduce potential glare in low light conditions.

Comfort: Comfort Moist Technology
Lens related-problems such as comfort, vision and deposits have been implicated as leading causes of contact lens drop out.9 In fact, eye care professionals and patients may feel the need to choose between vision and comfort when deciding among contact lenses. For this reason, attributes such as Comfort Moist Technology have been incorporated to help improve lens comfort. Comfort Moist Technology has two key features: a thin lens design to provide a natural feel throughout the day and a moisture-rich packaging solution to provide excellent comfort upon insertion. The thin rounded edge design (Figures 3 and 4) enables a smooth, gentle transition of the lid from the lens to the conjunctiva allowing for a more natural feeling on the eye and enhancing all-day comfort.

Vision: Spherical Aberration
Spherical aberration is the inability of the eye to focus light rays passing simultaneously through the center and the periphery of the eye. The retinal image appears blurred because the peripheral light rays are focused anterior to the retina (Figure 5). Spherical aberration can be a barrier to high-quality vision in low light, resulting in blurred vision, halos and glare.

Spherical aberration can either be inherent or induced. There is an inherent amount of spherical aberration in the average eye. In a study of 1,333 eyes (1,159 myopic and 174 hyperopic), a mean spherical aberration of +0.18 µm was reported for the myopic eyes and the age-matched hyperopic eyes.10 A conventional spherical contact lens does not consistently control spherical aberration across the power range. Spherical lens designs induce spherical aberration due to their curved spherical surfaces; negative spherical aberration for negative power lenses, and positive spherical aberration for positive power lenses, in proportion to their back vertex power.

Finite Element Modeling and High Definition Optics
One option for the correction of spherical aberration is to use advanced contact lenses that incorporate aspheric optics. Two components must be considered when designing spherical aberration-correcting aspheric contact lenses: inherent spherical aberration and induced spherical aberration as mentioned above. It is also important to consider that the optical properties of a soft contact lens that is soaking in solution differ from those of the same lens when placed on the eye. The wearers’ initial blinking upon insertion causes the lens to conform to the ocular surface (Figure 6). This conformation of the lens induces spherical aberration, the amount of which varies with the spherical power of the lens.11 To predict the behavior of a contact lens in this conformed state, a numerical-analysis technique called finite element modeling can be used.12

Finite element analysis creates a model of the structure under test conditions and subdivides the structure into small elements on which differential equations are solved to predict the behavior of each element as well as the whole structure. This type of modeling is used to predict the behavior of a contact lens in its conformed state and to subsequently design contact lenses in the state in which they are worn.

Finite element modeling was used to design lenses with High Definition Optics. These lenses are designed to reduce the positive spherical aberration that is naturally occurring in the human eye as well as reduce the spherical aberration induced by the contact lens on-eye to minimise halos and glare and bring all of the light rays to the same focal point to create clear, crisp vision all day – especially in low light (Figure 7).

Toric lenses also have been designed with High Definition Optics to reduce spherical aberration in all meridians, in quarter diopter steps across the power range. By controlling spherical aberration in all meridians, these lenses not only correct for astigmatism and spherical aberration, but also reduce secondary astigmatism.

Clinical Applications
Contact lenses that correct spherical aberration offer eye care practitioners a unique way to help improve visual quality for their patients. Unfortunately, specialists and patients alike often assume that halos and glare are an accepted side effect of contact lens wear. Prescribing a lens design that employs aspheric optics does not increase the difficulty of their fitting, because spherical aberration is symmetric and does not require a specific on-eye lens orientation like correcting for astigmatism.

Providers should educate themselves on the way various lens designs attempt to incorporate aspheric optics across a range of powers, as there are significant differences in the efficacy of each aspheric design. The newest generation of aspheric contact lens designs incorporate a population standard spherical aberration magnitude that is adjusted for specific lens powers, which improves the effectiveness of the aspheric design.

Conclusion
It is important to consider the complete lens-wearing experience when fitting patients with contact lenses. In addition to comfort and health, eye care practitioners should also take a closer look at patients’ quality of vision. The findings of the NSIGHT study revealed that vision is what patients most desire and highlighted that patients are not entirely satisfied with their current vision correction. In addition, glare, halos and blurry/hazy vision may be symptoms that are impacting their satisfaction. While spectacle use was most prevalent, the option of contact lens use was valued, including among astigmats.

Practitioners should consider whether spectacles and/or contact lenses will most benefit the patient based on his/her vision needs and lifestyle. The high rates of vision-related symptoms experienced with either modality suggests that patients would welcome improved vision correction with advanced options, such
as toric lenses.

Regardless of the modality prescribed or the vision disorder of the patient, there is a genuine need for practitioners to follow up with patients to gauge their satisfaction with the prescribed treatment. In line with these patients’ insights, vision and optical expertise remain fundamental in the development of new contact lens designs.

The results of the NSIGHT Study are providing eye care practitioners with new, and in some cases unexpected, insights into patients’ needs and preferences. Patients are looking for contact lenses that offer stable and consistent vision throughout the day without compromising comfort.

Eyecare practitioners should expect that achieving the best vision possible is of paramount importance to their patients and can be achieved with the latest generation toric contact lens designs.

Delivering What Patients
Need and Want

Historically, toric contact lenses have been more uncomfortable than spherical lenses. Now we have these new generation lenses that are very stable and have a great edge design. I had been using toric contact lenses for years and they were fine. They correct astigmatism, but patients would often tell me they see better when they put their eyeglasses on in the evening. Now, with aspheric optics correcting some of the higher-order aberrations, patients are telling me their vision with their contact lenses is better. They’re wearing their lenses longer because they see better with them, and they’re seeing better at night. They’re happier overall. They don’t drop out of lens wear down the line either.

Our intake form asks patients if they experience glare or halos, and staff ask again during pre-testing. We perform screening aberrometry on every patient and if I see higher-order aberrations, I use that as the starting point to explain how they can degrade vision and what we can do about it. Another thing I do in the exam room, which is simple but effective, is turn the lights down, put a white dot at the end of the room on the wall with a pen light, and ask patients to describe what they see while they’re wearing their current lenses. The ones who have spherical aberration will often tell me they see a “flare” or “a glow around the light.” Then I insert the new lenses with the aspheric optics and we repeat the process. Right away, patients usually say, “wow that light is now nice and pinpoint!”

The new edge designs are impressive. With some edge designs, I feel as if I have to be careful judging the movement of the lens. Some edges tend to clamp and bind to the conjunctiva, and even though the lens will move a millimeter, if I see the conjunctiva moving a millimeter, I’m not going to get adequate transport of oxygen and fluid and waste material in and out from behind the lens. This new edge design has really incorporated great comfort but also good movement, and it doesn’t bind.

David I. Geffen, O.D., FAAO was in private practice in La Jolla, California from 1982 to 1994 before joining Gordon Binder & Weiss Vision Institute where he is now Director of Optometric and Refractive Surgery. Dr. Geffen specialises in primary eye care, contact lenses, and refractive and cataract surgery services. He is an adjunct clinical faculty member of the Illinois College of Optometry.

Dr. Alexis Vogt is an Optical Physicist for Bausch + Lomb. She currently works with the Medical Affairs group to provide contact lens technical support for Professional Relations colleagues worldwide.

Dr. Marjorie J. Rah, OD, PhD is currently Manager, Global Medical Affairs, Vision Care Bausch + Lomb.

Dr. Greg DeNaeyer is the clinical director for Arena Eye Surgeons. His primary interests include specialty contact lens fitting. He is a Founding Fellow of the Scleral Lens Education Society and a Fellow of the American Academy of Optometry.

To earn your CPD points from this article, answer the assessment available at: mivisionclean2.flywheelsites.com/toric-lens-design

References:

1. Attebo K, Ivers RQ, Mitchell P. Refractive errors in an older population: the Blue Mountains Eye Study. Ophthalmology. Jun 1999;106(6):1066-1072.

2. Holden BA. The principles and practice of correcting astigmatism with soft contact lenses. Aust J. Optom. 1975;58:279-299.

3. Katz J, Tielsch JM, Sommer A. Prevalence and risk factors for refractive errors in an adult inner city population. Invest Ophthalmol Vis Sci. Feb 1997;38(2):334-340.

4. Richdale K, Sinnott LT, Skadahl E, Nichols JJ. Frequency of and factors associated with contact lens dissatisfaction and discontinuation. Cornea. Feb 2007;26(2):168-174.

5. Rumpakis J. New Data on Contact Lens Dropouts:
An International Perspective. Rev Optom. 2010(1).

6. Mack CJ, Merchea MM, Thomas H. A Global Survey Reveals Vision Needs of Highest Importance Amongst a Vision-Corrected Population. Optom Vis Sci. 2010;87:E-abstract:105233.

7. Mack CJ, Merchea M, Rah MJ. Incidence of vision-related symptoms in a contact lens-corrected global population survey. Global Specialty Lens Symposium.
Las Vegas, Nevada 2011.

8. Consumer Toric Needs Study: US. Millward Brown.December 2010.

9. Young G. Why one million contact lens wearers dropped out. Cont Lens Anterior Eye. Jun 2004;27(2):
83-85.

10. Kingston A, Cox I. Wavefront aberrations of the human eye – a large population sample. Optometry. 2011;82(6):351-352.

11. Cairns G. Enhancing contact lens design for complete performance. Optician. 2007(February):14-16.

12. Vogt AKS, Hovinga K, Schoof C, Stupplebeen R, Green T, Cox I. Finite element analysis conformation model of soft contact lenses. British Contact Lens Association Manchester, UK 2009.

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