Evaluation of Pollen Adhesion to Verofilcon-A Soft Contact Lenses

1. INTRODUCTION

Seasonal allergic conjunctivitis is usually caused by airborne allergens, such as the pollen of trees, grasses, and weeds, and worsens during the high pollen season. The typical signs of seasonal allergic conjunctivitis are mild to moderate itching, redness, and swelling of the conjunctiva [1, 2]. Soft contact lenses (SCLs) also cause giant papillary conjunctivitis (GPC), a subtype of allergic conjunctivitis. However, contact lens-induced GPC is not real allergic conjunctivitis, but is considered a chronic ocular inflammation [1, 3]. During wear, the SCLs accumulate tear film deposits3 including proteins [4, 5], lipids [6], and mucins [7]. The Food and Drug Administration Groups II and IV SCLs are high water content SCLs that accumulate more tear film components than Groups I and III low water content SCLs [5, 6]. The SCLs can easily trap various aeroallergens including tree and grass pollen, dust, smog, and cosmetic makeup. These allergens worsen the symptoms of allergic conjunctivitis and may cause conjunctival inflammation [8-10].

An earlier study suggested that the rate of adhesion Cryj 1, a major Japanese cedar pollen allergen, to SCLs was higher in the monthly replacement SCLs than the daily disposable SCLs or the 2-week frequent replacement SCLs [11]. Another study demonstrated that the pollen adhesion to daily disposable SCLs was higher on the colored SCLs than on the clear SCLs [12]. Additionally, pollen adhesion was lower in the silicone hydrogel SCL than in hydroxyethyl methacrylate (HEMA) CLs [12]. These results suggest that the daily disposable silicone hydrogel type of SCL may be better for patients with AC, especially during the pollen season.

Recently, a new 1-day disposable SCL (1DSCL) made of silicone hydrogel called verofilcon-A (PRECISION1™, Alcon Japan Ltd. Tokyo, Japan) was introduced to Japan. Verofilcon-A is made from a new high oxygen permeability (Dk; 90 × 10⁻¹¹ barriers) material with a 2–3-µm-thick surface with more than 80% water content and is a Class 1 ultraviolet blocker (≥ 90% of UVA, ≥ 99% of UVB) [13]. The verofilcon-A SCL has a smooth surface with the smoothing produced by SMARTSURFACE® Technology, and it is expected that pollen and protein components will not adhere to this type of surface as easily. However, whether there is less pollen adherence to verofilcon-A SCLs than other types of 1DSCLs has not been determined.

We examined the degree of pollen adhesion to the surface of verofilcon-A SCLs and compared the degree of pollen adhesion to verofilcon-A daily disposable SCLs to that of other major 1DSCLs available in Japan.

2. MATERIALS AND METHODS

3. RESULTS

3.1. Numbers of Pollen Particles Adherent to SCLs

Fig. (1) shows the pollen particles attached to the surface of the SCLs/200 μm × 200 μm area. The number of pollen particles adhering to the SCL was 98 ± 51 for CL1, 77 ± 36 for CL2, 57 ± 46 for CL3, 33 ± 16 for CL4, 25 ± 8 for CL5, 21 ± 8 for CL6, 14 ± 9 for CL7, 9 ± 5 for CL8, 6 ± 5 for CL9, 4 ± 4 for CL10, 3 ± 2 for CL11, 0 ± 0 for CL12, and 0 ± 0 for CL13 (Fig. 2). There were significant differences among the 13 groups (P<0.001).

Table 1.

SCL No.	Water Content (%)	Oxygen Permeability (Dk)	Oxygen Transmissibility (Dk/L)	Diameter (mm)	Base Curve (mm)	CT (mm)	Colored SCL	Surface (Ionic/ Non-ionic)	FDA group	USAN Nomenclature	Principal Components
1	38.6	8.5	12.1	14.2	8.7	0.08	Yes	Non-ionic	I	Polymacon	2-HEMA, EGDMA
2	38	12	24	14.5	8.7	0.05	Yes	Non-ionic	I	Polymacon	HEMA, EGDMA
3	42.5	11	13.75	14	8.6	0.08	Yes	Non-ionic	I	Polymacon	HEMA、NVP、MMA
4	38.5	10	14.3	14	8.7	0.07	No	Non-ionic	I	Polymacon	HEMA, EGDMA
5	38.5	10	20	14	8.7	0.05	No	Non-ionic	I	Polymacon	HEMA, EGDMA
6	38	8.5	12.1	14	8.7	0.07	No	Non-ionic	I	Polymacon	HEMA, EGDMA
7	58	25.68	36.7	14.2	8.6	0.07	No	Non-ionic	II	Omafilcon A	2-HEMA
8	59	22	24.2	14.2	8.6	0.09	No	Non-ionic	II	Hilafilcon-B	HEMA, NVP
9	58	28	33.3	14.2	8.75	0.084	No	Ionic	IV	Etafilcon-A	HEMA, MA
10	55	19.7	26.3	14.2	8.6	0.075	No	Ionic	IV	Ocufilcon-D	HEMA, MA
11	38	103	121	14.3	8.75	0.085	No	Non-ionic	V-I	Senofilcon-A	DMA, HEMA, PVP
12	Core33 /Surface80	140	156	14.1	8.7	0.09	No	Non-ionic	V-IV	Delefilcon-A	CE-PDMS, DMA, TRIS
13	Core51, /Surface80	90	100	14.2	8.5	0.09	No	Non-ionic	V-IV	Verofilcon A	mPDMS, GPDMS, NVP

EWC=Equilibrium water content; CT=Center thickness of contact lens; FDA=Food and Drug Administration; USAN=United States adopted names; HEMA=2-Hydroxyethyl methacrylate; EGDMA=ethylene glycol dimethacrylate; PVA=polyvinyl alcohol; NVP=N-vinyl-pyrrolidone; MA=methacrylic acid; DMA=N,N'-dimethyl acrylamide; PVP=polyvinylpyrrolidone; CE-PDMS=chain-extended polydimethylsiloxane; TRIS=Tris(trimethylsiloxy)silyl methacrylamide; mPDMS=mono-methacrylate poly dimethylsiloxane; GPDMS=Glycerol-functionalized polydimethylsiloxane; NVP=N-vinyl pyrrolidone.

Table 2.

-	Correlation Coefficients					Multivariate Analysis
Variables	R		(95% CI)	P Value		OR		P Value
Water Content (%)	-0.48		(-0.60 – -0.33)	<0.001		0.1		0.007
Oxygen Permeability (Dk)	-0.43		(-0.56 – -0.27)	<0.001		0		0.03
Oxygen Transmissibility (Dk/L)	-0.42		(-0.55 – -0.26)	<0.001		329.8		0.042
Diameter (mm)	0.14		(-0.03 – 0.31)	0.109		0		0.704
Base Curve (mm)	0.16		(-0.02 – 0.32)	0.075		>100		0.002
Center Thickness	-0.33		(-0.48 – -0.17)	<0.001		>100		0.023
SCL color (clear=0/color=1)	-		-	-		>100.0		<0.001
Surface charge (non-ionic=0/ionic=1)	-		-	-		0		<0.001
FDA classification	-		-	-		>100.0		0.002

3.3. Factors Affecting Adhesion of Pollen Particles to SCLs

There were significant negative correlations between the number of pollen particles adhered to the SCLs and some parameters of SCL, such as the water content (r = −0.48), oxygen permeability (r = −0.43), oxygen transmissibility (r = −0.42), and center thickness (r = −0.33) (Table 2).

Correlations between the number of pollen particles adhered to SCLs and parameters of SCLs were calculated with the two-tailed Pearson’s product moment formula. Independent determinants of the number of adhered pollen particles were investigated by multiple logistic regression analysis. R = Pearson’s correlation coefficient; CI = confidence interval; OR = odds ratio.

Fig. (4) shows the correlations between the portion of the pollen adhesion area and each characteristic of the SCLs. The area of pollen adhered to SCLs was significantly higher for colored SCLs than for clear SCLs (2.73 ± 1.97% vs. 1.03 ± 1.01%, P<0.001). The area of pollen adhered to SCLs was negatively correlated with water content (r = −0.51), oxygen permeability (r = −0.54), oxygen transmissibility (r = −0.54), and center thickness (r = −0.42).

The pollen adhesion area was smaller in the silicone hydrogel SCLs (SCL11–13; 0.05 ± 0.16%) than in the hydroxyethyl methacrylate HEMA SCLs (CL1 to CL10, 1.84 ± 1.45%, P<0.001). The portion of pollen adhesion area was lowest in both silicone hydrogel SCLs made with delefilcon-A (0.00 ± 0.00%) and verofilcon-A (0.00 ± 0.00%) (Fig. 4).

4. DISCUSSION

Our results showed that the number of pollen particles adhered to 13 different 1DSCLs varied from 0 to 185 particles per 200 × 200 µm area. Pollen adhesion was higher in the colored SCLs and lower in the silicone hydrogel SCLs. These results indicate that the degree of pollen adherence to the surface of the new verofilcon-A clear silicon hydrogel SCLs was very low.

In general, SCLs made of silicone hydrogel have the advantages of high oxygen permeability and resistance to drying [15]. However, some SCLs made of solid materials are still not comfortable to wear. To overcome the weaknesses of these silicone hydrogel materials, verofilcon-A SCL has succeeded in improving the wearing comfort with its unique technology called “SMARTSURFACE™ Technology” [16]. The surface of the verofilcon-A SCL has a high water content of 80% or more, which is accomplished by covering the surface of the SCL with a highly water-retaining hydrophilic polymer. SMARTSURFACE® is based on a manufacturing process in which the CLs are immersed in a liquid filled with a water-soluble polymer containing a hydrogel polymer and polyacrylic acid (PAA). PAA is a very hydrophilic polymer capable of absorbing large amounts of water, producing a “hydrogel.” PAA is a major contributor to the high water content of verofilcon-A SCL, which has a 51% water core wrapped in a gel-like outer layer that transitions to 80% at the surface [16]. In the processing stage of SMARTSURFACE™ Technology, this hydrophilic polymer solution expands the lens material to create small and narrow pores on the lens surface that are 2–3 microns in diameter [16]. The water-loving PAA polymer penetrates the open pores and is locked into place, creating a micro-thin layer of moisture. In addition, the heating process crosslinks the PAA polymer with a wetting agent consisting of a copolymer of polyamide amine and polyacrylamide-acrylic acid. This thin layer of PAA on the lens surface provides long-lasting moisture, support for stabilizing the tear film, and smoothness of the lens surface. These properties lead to long-lasting comfort and clear vision, according to the company’s literature [16]. The moderately hard structure in the center of the SCL makes it easier for SCL wearers to handle it when inserting and wearing these SCLs. In fact, 82% of new SCL wearers have reported that verofilcon-A SCLs are easy to place on the cornea and 72% agreed that they are easy to remove at the end of the day [17]. Furthermore, in a questionnaire survey of SCL wearers, verofilcon-A SCLs were reported to provide high quality of vision, comfort of wearing, and easy handling of wearing [18, 19]. SMARTSURFACE™ Technology is expected to not only improve the comfort of wearing SCLs but also reduce the adhesion of proteins and air dust on the SCL surface. In fact, our results showed that verofilcon-A SCLs had lower pollen adhesion than the other SCLs. As parameters for SCLs other than verofilcon-A, the water content, oxygen permeability, and oxygen transmissibility had a negative and significant correlation with the number of pollen particles adhered to the SCLs (Table 2). In addition, the colored SCLs and non-ionic HEMA SCLs had a high pollen adhesion number (Table 2). Generally, SCLs made with HEMA material have more protein adhesion than silicone hydrogel SCLs [20]. Because the silicone materials are hydrophobic and lipophilic, the silicone SCLs repel tears and are prone to the adherence of lipid particles. Therefore, to improve the wettability of the SCL surface, silicone hydrogel SCLs are coated with a hydrogel-rich material [20]. SCLs are coated with a variety of substances after being soaked in a dispersion of positively charged particles (DOWEX™) [20]. Therefore, positively charged pollen particles do not easily adhere to the SCLs treated with a positively charged material.

We used SCLs made of different materials: polymacon, omafilcon A, hilafilcon-B, etafilcon-A, ocufilcon-D, senofilcon-A, delefilcon-A, and verofilcon-A. All of these are very popular SCLs available in Japan. Of the 13 types of lenses, 11 lenses, excluding delefilcon-A and verofilcon-A, were different types of SCLs from the SCLs examined in earlier studies [12]. Nevertheless, the results regarding pollen adhesion to the SCL surface were similar to those of earlier studies using different lenses [12]. These results support the idea that SCL materials are involved in the degree of pollen adhesion to SCLs. That is, SCLs of non-ionic HEMA material, low water content, low oxygen permeability, and low oxygen transmissibility are those that pollen tends to adhere to.

The pollen adhesion area was not related to the base curve of the SCLs (Fig. 4). We examined only the center part of the SCL; therefore, the curvature of the entire surface of the SCLs probably did not affect pollen adhesion. In addition, there were only 4 types of lens curvatures, 8.5 mm, 8.6 mm, 8.7 mm, and 8.75 mm, which may have contributed to the absence of statistical significance. The center thickness of the SCLs was negatively correlated with the degree and area of pollen adhesion (Fig. 4). The center thickness of SCLs ranged from 0.05 to 0.09 mm (Table 1). The thickness of silicone hydrogel SCLs with less pollen adhesion was very thick (0.085–0.09 mm, CL11, CL12, and CL13; (Table 1). Therefore, the relationship between SCL center thickness and pollen adhesion may be influenced by the properties of the SCL material, especially the silicone hydrogel material.

This study has several limitations. First, the amount of pollen used was much higher (approximately 2,500 pollen/mm² dropped on the surface of SCLs) than the general amount of pollen floating in the air (approximately 100 particles/cm²/day in Tokyo from March to April 2021). Second, the pollen adhesion experiments were only verified using 1DSCLs. The properties of 2-week and monthly replacement SCLs or conventional SCLs deteriorate over a long period of use and easily adsorb proteins. Therefore, rather than the 1DSCLs, a study of pollen adhesion to the 2-week frequent replacement SCLs or conventional SCLs may be useful for CL users.

CONCLUSION

In conclusion, the adherence of pollen and protein to SCL was lowest for verofilcon-A processed with SMART SURFACE™ Technology. Thus, verofilcon-A, like the delefilcon-A, maybe the best SCL for users with hay fever or allergic conjunctivitis.

REFERENCES