Photorefractive keratectomy (PRK) is an established procedure for the excimer laser correction of refractive errors.1 One of the major limitations of PRK is the postoperative pain and delay of visual recovery while epithelial healing takes place. Soft hydrogel contact lenses have been widely used as a bandage to reduce pain and optimise the epithelial healing process, both in PRK and subsequently LASEK.2 In this situation, the bandage contact lens is typically inserted at the time of surgery and used on a continuous extended wear basis for 2–7 days. The most commonly used type of lens for this indication has been conventional hydrogel material. However these lenses are not intended for extended wear, and do not provide adequate corneal oxygenation, which may inhibit the healing process.3–6 Following the introduction of silicone hydrogel lenses, there is a superior option to maintain oxygenation during epithelial regeneration. Existing studies support this notion, with faster re-epithelisation and reduced discomfort using silicone hydrogel lenses compared to conventional hydrogel lenses.3,4,7–10 Different silicone hydrogel lenses vary considerably with respect to a number of characteristics in addition to oxygen permeability alone (Table 1). These include water content, material stiffness (Young's modulus), thickness, edge profile, surface smoothness, surface treatments, hydrophobicity, size and base curve. The effect of these characteristics individually on pain and epithelial healing is not well elucidated; nevertheless there may be considerable variation in the performance of different silicone lenses. In the current study we determined the relative merits of two silicone hydrogel lenses when used as a bandage following transepithelial photorefractive keratectomy.

This was a prospective double masked contralateral eye study carried out at a refractive surgical centre in Heraklion, Greece. After undergoing transepithelial PRK for myopia, a Comfilcon A (Biofinity, Coopervision, Fairport, NY) silicone hydrogel lens was inserted in one eye, with a Senofilcon A (Acuvue Oasys, Johnson & Johnson, Jacksonville, FL) lens in the contralateral eye. Patients were included subject to informed consent, and prior ethical approval was obtained from the institutional review board. The research conformed to the tenets of the Declaration of Helsinki. Patients were excluded in the presence of any ocular or systemic condition which might affect epithelial healing or pain perception. In particular patients with significant dry eye or any corneal epithelial abnormality were excluded.

The study population consisted of 50 eyes of 25 patients. One patient was excluded due to inadequate follow-up, leaving 48 eyes for analysis. The mean age was 31 years (SD 11: 22–41). Mean spherical equivalent error was −4.5D (SD 1.8: −8 to −1.5). Baseline comparison of Comfilcon and Senofilcon groups demonstrated no significant difference in spherical equivalent (−4.5D vs. −4.5D), astigmatism (−0.7D vs. −0.8D) or preoperative vision (0.00 vs. 0.00 LogMAR), with P<0.001 for all variables. All other factors were constant due to the contralateral eye design, and in all cases utilising Mitomycin C this was in both eyes. Raw clinical data for each patient are provided as Appendix 1 to this paper.

Pain

Mean pain score at day 1 was 4.6 (SD 2.7: range 0–10) in the Comfilcon group, and 1.5 (SD 2.5: range 0–7) in the Senofilcon group (Fig. 1). The pain scores in the Comfilcon group were statistically significantly greater (P<0.005 paired 2 tailed T-test). For each patient, the pain score was greater in the eye with Comfilcon lens in 18 (75%), equal in both eyes in 5 (21%) and greater in the eye with Senofilcon lens in 1 (4%), with significantly more patients finding the Comfilcon lens more painful (P=0.01 Sign test) (Fig. 2).

Figure 1.

Mean postoperative characteristics of epithelial healing, vision and pain comparing a second and third generation silicone hydrogel bandage contact lens after transepithelial photorefractive keratectomy. Pain was significantly higher in the Comfilcon A group (P<0.05).

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Figure 2.

Inter-eye comparison of subjective pain scores between a second (Senofilcon A) and third generation (Comfilcon A) silicone hydrogel bandage contact lens in contralateral eyes after transepithelial photorefractive keratectomy. Each point represents one patient, with points below the dashed line indicating that pain was lesser in the eye with a Senofilcon A lens.

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The use of silicone hydrogel lenses following surface excimer refractive surgical procedures has become recognised to offer benefits with regard to epithelial healing.3,4,6,8 There has been a progressive development of desirable features of such lenses. First generation silicone hydrogel lenses require hydrophilic surface treatments, and have relatively high modulus and low water content. Second generation lenses have higher water content due to internal wetting agents. Third generation lenses have lower modulus, while maintaining higher water content without internal wetting agents.6

In this study we evaluated two silicone hydrogel lenses used as therapeutic bandages following PRK surgery. One lens, the Acuvue Oasys, is composed of Senofilcon A, a second generation silicone hydrogel material. This material differs from earlier first generation materials in having an internally incorporated wetting agent (polyvinyl pyrrolidone), rather than depending on surface treatments to maintain wetting. As a result the material has a moderately high water content (38%) and is relatively low in stiffness (modulus 0.73MPa).3,11–13 By comparison the Biofinity lens is composed of the third generation material, Comfilcon A. This is an inherently wettable polymer, which, like Senofilcon requires no surface treatment for wettability. As a result the Comfilcon material has both a higher water content (48%) and higher oxygen transmissibility (Dk 128 units) compared to Senofilcon, while maintaining a low stiffness modulus of 0.75MPa.6,13,14 Surface characteristics also differ, and the Comfilcon and Senofilcon lens surfaces have been shown to differ by atomic force microscopy, with some evidence of a smoother surface in Comfilcon lenses.13,14

Given these differences of Comfilcon to Senofilcon in these various parameters, it might be expected to offer some advantage as a bandage lens. In this study, however, we found no difference in the speed of epithelial healing between the two lenses. The subjective assessment of epithelial healing quality did favour the Comfilcon lens, with a smoother epithelial surface as evidenced by a lower proportion of eyes with a visible central raphe, but this difference was not statistically significant, and appeared to be of little clinical relevance. There was also no difference in early visual recovery following healing.

The main finding of this study was of superior pain control following PRK with the Senofilcon compared to the Comfilcon lens, with significantly lower pain scores. This is consistent with the findings of other previous studies. Razmjoo et al. compared a Senofilcon A to lotrafilcon A lens for PRK and found better pain and discomfort control with Senofilcon.11 Qu et al. compared a Galyfilcon A lens to Balafilcon A for LASEK and found better pain control with Galyfilcon.7 This is notable because Galyfilcon is a precursor to the development of Senofilcon, and both share many chemical characteristics. Grentzelos et al. compared lotrafilcon A and lotrafilcon B for PRK and found no difference in pain.15 Plaka et al. compared Asmofilcon A to Lotrafilcon B following PRK, but did not assess subjective pain.16

The mechanism of pain relief by contact lenses is not well elucidated. Although the Comfilcon lens appears equivalent or superior in a range of material characteristics, there may be other factors involved in pain relief. It is notable that the Senofilcon lens in this study demonstrated significantly reduced movement compared to the Comfilcon lens. The potential benefits of tight fit for bandage use has been suggested by some authors.15,17 In this study, a base curve of 8.4 was used for the Senofilcon A lens, while the Comfilcon A lens was of base curve 8.6. It is thus possible that a tighter fit with reduced mobility of the Senofilcon lens accounts for the greater relief of pain, by preventing blink effects on the exposed nerve endings or friable nascent epithelium.6

The expected performance of various silicone hydrogel lenses when used in a therapeutic role for pain or epithelial healing depends on a number of factors, and may not easily be predicted on the basis of material or geometry characteristics. Thus, clinical evaluation of lens types is valuable to determine the optimal lens choice in this setting.

The study was performed with informed consent and approval by the Local Ethics Committee. Research adhered to the tenets of the Declaration of Helsinki.

No financial support was received for this submission.

None of the authors have conflict of interest with the submission. No author has any financial interest in the subject matter.