Evaluation of surface water characteristics of novel daily disposable contact lens materials, using refractive index shifts after wear

Abstract

PurposeContact lens wearers today spend much time using digital display devices. Contact lens manufacturers are challenged to develop products that account for longer periods of time where blink rate is reduced and tear-film evaporation rate is increased, affecting both visual acuity and comfort. Two manufacturers recently introduced novel daily disposable contact lenses with high surface water content. The objective of the present study was to compare surface water characteristics before and after initial wear of recently introduced nesofilcon A and delefilcon A high surface water lenses with those of etafilcon A lenses.Patients and methodsTwenty healthy subjects wore each of the three lens types studied in a randomly determined order for 15 minutes. After each wearing, lenses were removed and the surface refractive index (RI) of each lens was immediately measured.ResultsThe mean RI of the unworn delefilcon A lens was 1.34, consistent with water content in excess of 80%. After 15 minutes of wear, the surface RI shifted to 1.43, consistent with its reported 33% bulk water content. In contrast, the mean surface RI of the nesofilcon A lens was 1.38, both initially and after 15 minutes of wear, and that of the etafilcon A lens was 1.41 initially and 1.42 after 15 minutes of wear.ConclusionThe surface of the delefilcon A lens behaves like a high water hydrogel upon insertion but quickly dehydrates to behave like its low-water silicone-hydrogel bulk material with respect to surface water content during wear, while both nesofilcon A and etafilcon A lenses maintain their water content during initial wear. The nesofilcon A lens appears unique among high water lenses in maintaining high surface and bulk water content during wear. This is important because changes in surface RI due to dehydration are reported to lead to visual aberration affecting user experience.

Evaluation of binocular function among pre- and early-presbyopes with asthenopia

“… 6 This phenomenon is especially significant for contact lens wearers because the resultant tear film disruption leads to visual aberration, due to both altered light refraction through the lens and lens dehydration that in itself alters lens geometry. 17 Not surprisingly, the incidence of CVS is greater in lens wearers, especially after 6 hours of computer use. 18 The use of other digital technologies with flat-panel displays such as cell phones, tablets, and e-readers is likewise associated with the symptoms of CVS.…”

<p>Tear Film Characteristics During Wear of Daily Disposable Contact Lenses</p>

“…Therefore, maintaining a consistent optical surface is important in order to reduce light scatter and prevent optical aberrations. 1 For this reason, it is essential to have adequate tear function and maintain a clean, highly wettable lens surface. 2 Contact lens wear has the potential to alter both integrity and stability of the tear film, which in turn will affect the quality of vision.…”

Use of a novel extended blink test to evaluate the performance of two polyvinylpyrrolidone-containing, silicone hydrogel contact lenses

“… 5 The consequences of such prolonged digital display viewing upon both visual acuity and comfort were recently described. 6 Briefly, the digital display environment results in decreased blink frequency, increased tear evaporation, incomplete blinking, decreased tear stability, and tear film disruption in both naked eyes 7 – 10 and the eyes of the contact lens wearer 11 , 12 alike. In the latter case, this manifests as blurry or fluctuating vision that may indicate a lens surface not retaining water.…”

“…23 While lenses of lower water content have been reported to dehydrate less than those of higher water content, and silicone hydrogels (typically of lower water content) less than traditional hydrogels 21 , 24 (typically of higher water content), 25 recent advances in material and surface chemistry resulted in newer high water lenses such as nesofilcon A that does not follow this trend. 6 Further studies to advance understanding of the chemical and surface properties of lens polymers that maintain water in both low and high water traditional hydrogel and silicone hydrogel lenses will drive development of future lens generations.…”

“…The ramifications of contact lens dehydration upon both visual acuity and comfort were recently described. 6 Briefly, lens dehydration both disrupts the lens tear film 26 and effects subtle changes in lens dimension; 27 these phenomena lead to light scatter and visual aberration, 13 , 28 , 29 as well as contact lens-induced dry eye. 30 …”