Lens and solution properties in patients with and without midday fogging

Abstract

Introduction:

Midday fogging is a complication of scleral lens wear that interrupts clear vision during the course of wear. Scleral lenses can be made with a variety of gas permeable materials, sizes and surface treatments, and various solutions are available for storing the lenses and for filling them before application on the eye. Many of these factors have been implicated as possible contributors to midday fogging. This study explored the lens and solution properties in habitual scleral lens wearers with and without midday fogging.

Methods:

In this prospective study, 48 habitual scleral lens wearers were evaluated and asked to report whether they experienced midday fogging, if they removed their lenses during the day and completed the Ocular Surface Disease Index (OSDI), which is a validated tool for dry eye assessment. Lens parameters (material, coatings and diameter) and lens storage and filling solutions were recorded. Backward elimination of regression terms evaluated the lens and solution properties in those with and without fogging. OSDI scores were compared using Mann-Whitney analysis.

Results:

Collectively, the lens properties and solutions accounted for 27.7% of the variance related to midday fogging. None of the factors alone made a significant impact upon midday fogging. The median (interquartile range) OSDI score for those with fogging [37(35)] was significantly different from those without fogging [10(15)], with the scores corresponding to severe dry eye and normal eyes, respectively.

Conclusion:

Scleral lens wearers with midday fogging exhibited similar symptoms to patients with severe dry eye. Lens and solution characteristics may play a small role in patients with midday fogging, although changing just a single factor is not likely to impact its presence.

Introduction

Midday fogging is a complex and poorly understood phenomenon which has been reported with scleral lens (SL) wear.^1–4 Symptoms of midday fogging include hazy or foggy vision which worsens over time and may necessitate periodic lens removal, refilling with fresh solution and reapplication, thus increasing the burden of care associated with SL wear. These symptoms have generally been attributed to increases in particulate debris or generalised loss of optical clarity within the post-lens fluid reservoir during SL wear.^2,5,6 Up to 20%−46% of patients who wear SL may experience this phenomenon.^1,3,7 Various causes for the increase in turbidity have been proposed. The earliest investigations into the phenomenon largely focused on characteristics of lens fit. Misalignment between the lens landing zone (LZ), also referred to as the lens haptic, and conjunctival tissue was suspected to allow for excessive tear exchange, which could carry debris into the post-lens fluid reservoir.^7–9 If this was the case, then utilisation of advanced LZ designs that optimise alignment between the lens and the anterior ocular surface should prevent midday fogging. However, a study by Schornack et al. showed similar rates of fogging regardless of LZ design in a retrospective multi-centre cross-sectional study.³ Additionally, Tse et al. found that tear flow under a scleral lens did not affect symptoms of midday fogging.¹⁰ Excessive post-lens fluid reservoir (FR) depth has also been implicated in the development of midday fogging, but clinical evaluations of the relationship between FR depth and midday fogging have yielded mixed results.^1,7,11,12

Because scleral lenses are highly customisable and many different solutions and parameters are used by scleral lens wearers, lens and solution properties have been explored as possible factors in midday fogging. Solutions used in the care and application of SL have also been suggested as contributing factors to midday fogging. A study using an unpreserved scleral filling solution with an ionic composition matching the tear film showed a decrease in symptoms of midday fogging.¹³ Similarly, an additional investigation of a similar solution containing electrolytes found improvements in the objective quality of vision compared with unpreserved saline without electrolytes.¹⁴ It has been suggested that adding high viscosity, ion-containing preservative-free artificial tears to the saline used for filling the post-lens FR may alleviate midday fogging in some patients.⁴ Additionally, surface properties of SL have been explored as possible factors affecting midday fogging. Mickles et al. explored the effects of a novel lens surface treatment on a number of factors which affected lens performance, including the frequency of foggy vision. Patients wearing treated lenses experienced significantly less frequent foggy vision than those wearing untreated lenses.¹⁵

Peer-reviewed literature on the condition has provided some insights into the origins of midday fogging and possible mitigation strategies, but knowledge gaps remain. Many studies have looked at the impact of short-term lens wear on healthy subjects; however, these results may not be generalisable to patients with eye disease who wear lenses for long periods of time. Existing observational investigations of actual scleral lens patients have featured small sample sizes and generally focused exclusively on a single factor associated with fogging, despite the multifactorial nature of the problem. Retrospective studies are limited to information that may be contained in patients’ medical records; specific information on all factors which may contribute to midday fogging may not be collected routinely as part of SL follow-up evaluation. Furthermore, most published literature ignores the fact that symptoms may be caused by something other than debris in the FR, such as front surface deposits or corneal oedema.⁵

In this prospective multi-centre observational study, established SL wearers were enrolled when they presented for follow-up evaluation. This design allowed for ascertainment of the percentage of patients who reported midday fogging subjectively, and facilitated standardised collection of data which may be implicated in the development of midday fogging. This investigation explored the role of lens and solution properties and the symptoms of patients with and without subjective reporting of midday fogging.

Methods

This prospective multi-site observational study conformed with the Declaration of Helsinki and received approval from the Institutional Review Board at The Ohio State University. Eligible participants were habitual SL wearers in one or both eyes, who wore their lenses for a minimum of 6 days per week for at least 5 hours each day. Participants must have worn their current lens design for at least 6 months. Subjects whose lens designs had been modified during the previous 6 months were excluded from participation in the study. During the study visit, participant age, gender, race and ethnicity were collected, along with the indication for wearing SL. Lens wearing schedule (hours of wear/day and days of wear/week) and the age of the current lenses was recorded. The parameters of the current lenses (material, LZ design, lens coating) were documented along with the types of solution used for lens storage and to fill the lens prior to application. Participants were asked if they experienced midday fogging and if they removed and reapplied their lenses during the day, but they were not asked to specify in which eye(s) the fogging occurred. Participants completed the Ocular Surface Disease Index (OSDI),¹⁶ which has been used in previous studies of midday fogging.¹³

Examination data was collected at all sites and recorded using REDCap (project-redcap.org/).^17,18 Regression analysis of was used to compare participants with and without midday fogging. A backward elimination of terms was completed to explore lens and solution factors.¹⁹ Anderson-Darling testing was performed to evaluate the normality of the OSDI, hours of daily lens wear and days of lens wear each week. Mann-Whitney analysis compared the OSDI scores and wear time for those participants with and without reported fogging. Descriptive statistics are also presented, as well as median and interquartile range (IQR) values for those parameters which were not normally distributed. Statistical analysis was performed using MiniTab version 21.3.1 (minitab.com).

Results

Forty-eight participants (29 female and 19 male) with a mean (standard deviation) age of 49.4(15.0) years were enrolled in the study. Thirty-seven participants identified as White, two as Asian, six as Black and three as more than one race; five participants identified as Hispanic and 43 reported not being of Hispanic ethnicity. Thirty-five participants wore SL in both eyes and 13 wore SL in one eye. No adverse events were reported throughout the study.

The mean age of the current SL was 15.7(8.3) months. Average wearing time per day was 12.4(3.0) hours, with mean of 6.7(0.7) days of wear per week. Indications for scleral lens wear included corneal irregularity (27), ocular surface disease (17), refractive error correction and one participant had neurotrophic keratopathy secondary to trigeminal neuralgia. Table 1 reports the demographics, indications for SL wear, lens properties and solutions used for participants with and without midday fogging.

Table 1:

Demographics, indication for lens wear, lens parameters, and solution usage for those participants with subjective midday fogging and those without subjective midday fogging.

	Midday Fogging (n=27)	No Midday Fogging (n=21)
Age	50.8 ± 14.7	47.7 ± 15.1
Gender	14 (51.8%) female	15 (71.4%) female
Indication for Scleral Wear
Keratoconus	9 (33.3%)	11 (40.7%)
Irregular cornea (not keratoconus)	4 (14.8%)	3 (14.3%)
Ocular Surface Disease	12 (44.4%)	5 (23.8%)
Refractive error only	1 (3.7%)	2 (9.5%)
Other	1 (3.7%)*	0
Factors included in ANOVA analysis
Lens Diameter	17.4 ± 1.2 mm	17.6 ± 1.3 mm
Lens Haptic Design
Sphere	7 (25.9%)	2 (9.5%)
Toric	5 (18.5%)	5 (23.8%)
Quadrant specific	15 (55.6%)	14 (66.7%)
Lens Material
Hexafocon	4 (14.8%)	3 (14.3%)
Roflufocon	20 (74.1%)	16 (76.2%)
Tisilfocon	1 (3.7%)	1 (4.8%)
Oprifilcon	2 (7.4%)	1 (4.8%)
Lens coating
No coating	2 (7.4%)	1 (4.8%)
Plasma coating	16 (59.3%)	7 (33.3%)
Hydrapeg coating	9 (33.3%)	13 (61.9%)
Lens Storage/Disinfection
Hydrogen peroxide	23 (85.2%)	17 (81.0%)
Multipurpose	4 (14.8%)	4 (19.0%)
Filling Solution	n=24 (3 used > 1 soln or did not know)	n=19 (3 used more than one)
0.9% Preservative Free (PF) Sodium Chloride (saline)α	9 (37.5%)	2 (10.5%)
Lacripureα	5 (20.8%)	6 (31.6%)
Nutrifillβ	0 (0%)	3 (15.8%)
Purilens§	7 (29.2%)	5 (2.6%)
ScleralFil§	1 (4.2%)	1 (5.2%)
Serum tears with PF saline	1 (4.2%)	0 (0%)
Celluvisc with PF saline	1 (4.2%)	2 (10.5%)

^*(neurotrophic keratopathy 2° to trigeminal neuralgia)

^αUnbuffered filling solution

^βFilling solution buffered with phosphate

^§Filling solution buffered with borate

Comparisons were made between participants with and without self-reported midday fogging. Of the 35 participants who wore SL binocularly, all but one wore lenses of identical diameter and LZ design in each eye. One participant wore lenses that differed by 0.5 mm in diameter between their right and left eyes. For analysis, data from this participant’s right lens (the larger diameter) was used in the analysis. All participants who wore lenses binocularly used identical care products for both lenses, and all had identical coatings (or lack thereof) on both lenses.

Twenty-seven participants (56.3%) subjectively reported midday fogging. Of these, three reported that they did not remove their lenses during the day. Twenty-six participants (54.2%) reported removing lenses during the day, although two of these participants denied experiencing fogging but nevertheless reported midday lens removal.

Regression analysis evaluated the presence of midday fogging using backward elimination of terms. Factors used included lens diameter, lens haptic design, lens material, storage solution, filling solution and lens coating. With this model, the R-squared value found that these factors accounted for 27.7% of the variance related to midday fogging. Despite these R-squared values, no factor was individually significant. The least significant factor was removed at each step, and R-squared decreased by a small amount with the removal of each factor. All factors in this model are included in Table 1. Additionally, the model was also analysed with filling solution grouped as pH buffered or unbuffered, and also by unbuffered, pH buffered with borate and pH buffered with phosphate. In all of these models, the filling solution and all other factors were not significant in the population examined.

Analysis of wear time and OSDI scores indicated that the distributions were not normal; therefore, non-parametric comparisons were made. The median (IQR) wear time was 14 (5) and 12 (4) hours per day for the participants who did and did not self-report midday fogging, respectively. This difference was not significantly different (p=0.08). Both groups wore lenses for a median of 7(0) days per week. The median (IQR) OSDI score for the participants who did and did not self-report midday fogging was 37 (35) and 10 (15), respectively. Mann-Whitney analysis indicated this difference was significant (p=0.02).

Discussion

Midday fogging is a complex phenomenon that is likely due to a combination of factors unique to each individual’s disease and its severity, specific tear film parameters for each individual, interactions between the lens and ocular surface structures such as eyelids and conjunctiva, along with additional factors that have yet to be considered. The findings of the present study suggest that combinations of the lens design and solution properties may have a small collective impact on midday fogging; but in this group of participants, there was not a single factor related to lenses or solutions that individually impacted the patient experience of midday fogging.

The OSDI test was designed to assess subjective dry eye symptoms, which overlap somewhat with symptoms of midday fogging; the instrument has been used in a previous study of SL wearers who reported midday fogging.¹³ Participants who reported midday fogging in the current study had a median score of 37, which falls in the range of severe dry eye (> 33), while the participants without midday fogging had a median OSDI score of 10, which is considered in the normal range (< 12).²⁰ Participants were not asked if they had been diagnosed with dry eye before or during SL wear, so it is possible that this large difference was confounded by symptoms specific to ocular surface disease. However, this association could be an important factor when assessing both dry eye and midday fogging in SL wear, since inflammation is known to be associated with dry eye disease,²¹ and has also been implicated in midday fogging.³

Limitations of this study include the fact it relied upon self-reporting of midday fogging by participants. It is possible that some individuals reported symptoms associated with lens surface deposits rather than post-lens FR turbidity. Furthermore, participants were not asked to specify laterality. Given that people generally proceed through life with both eyes open, it was thought that subjects may have considerable difficulty identifying the eye in which fogging occurred. Individual participants may have different definitions for midday fogging and varying thresholds for finding these symptoms bothersome. This is apparent with differences in reports of midday fogging compared to the midday removal of lenses. Lens centre thickness was not collected here, and may be an additional parameter to explore in future studies. Additionally, the presence of ocular findings, such as dry eye, inflammation and lens fitting parameters were not evaluated in this investigation and warrant additional study.

Despite these limitations, this study does address some of the challenges inherent in previous study designs. Data was collected prospectively using a standardised form. The study captured the long-term experience of current SL wearers. Lack of a single definitive causative factor for midday fogging may seem disappointing, but does acknowledge and emphasise the myriad of complex factors which likely interact to cause these symptoms. Clinicians are encouraged to consider all of these factors as they attempt to mitigate symptoms of midday fogging in their patients.

Key Points:

• Lens and solution properties collectively accounted for 27.65% of the variation in midday fogging in this study.

• No individual lens or solution property individually impacted the presence of midday fogging.

• The median Ocular Surface Disease Index score of participants with and without midday fogging met the criteria of “severe” and “normal”, respectively.

Data Sharing Statement

Data reported in this manuscript are available within the article. Study-level data including the study protocol are available. To request access to the data, the researcher must sign a data use agreement. All proposals should be directed to Jennifer Swingle Fogt (fogt.78@osu.edu) for up to 36 months following article publication.