Survey-based Estimation of Corneal Complications Associated With Scleral Lens Wear

Abstract

The benefits of scleral lens (SL) wear have been described in cross-sectional and retrospective studies; however, the frequency of complications associated with SL wear has not, to our knowledge, been determined. From a survey of SL practitioners, we estimated the period prevalence over 1 year of corneal complications that required SL wearers to discontinue lens wear. In a sample of 72,605 wearers, SL wear was discontinued for the following complications: corneal edema, 1.2%; corneal neovascularization, 0.53%; microbial keratitis, 0.45%; and limbal stem cell deficiency, 0.20%. This study design allowed for calculation of period prevalence of these complications rather than complication incidence rates. Information presented in this report may be useful in clinical decision-making as well as for future study design.

Scleral lenses (SL) are currently prescribed primarily for patients with corneal irregularity and ocular surface disease.¹ Visual and physiologic benefits of wearing SLs have been described,² but risks of corneal complications associated with SL wear are less clearly defined. Isolated case reports^{3, 4} and retrospective reviews^{5, 6} have described microbial keratitis (MK) in SL wearers. Other corneal complications such as perilimbal corneal epithelial bullae,⁷ transient epithelial bullae,⁸ and corneal endothelial blebs⁹ have also been reported. To our knowledge, the frequency of these complications has not been described. The estimated incidence of corneal complications associated with SL wear would be helpful for practitioners and patients as they weigh the relative benefits of this type of lens against its risks. This brief report details results of a survey-based estimate of the percentage of SL wearers who developed MK, corneal neovascularization, corneal edema, and limbal stem cell deficiency during 1 year.

Methods

The study was approved by The Ohio State University Institutional Review Board and designed and administered using REDCap (Research Electronic Data Capture) software¹⁰ housed at The Ohio State University. We conducted a survey of SL practitioners from November 8, 2019, through March 31, 2020. The survey was distributed to attendees at the International Summit of Specialty Contact Lenses (November 2019, Rome, Italy), attendees at the Global Specialty Lens Symposium (January 2020, Las Vegas, NV), members of the Scleral Lens Education Society, and participants in previous surveys who agreed to be contacted for future studies. Links to the survey were posted on a private Facebook page for SL practitioners and were also included in 2 online newsletters (I-Site and BCLA).¹⁰ The survey asked the practitioners to identify their country of residence, primary practice modality, and years of experience fitting scleral lenses. Participants were also asked to estimate the number of patients wearing SLs that they had evaluated during the preceding year, and to report the number of patients for whom SL wear was either temporarily or permanently discontinued because of MK, corneal neovascularization, corneal edema, or limbal stem cell deficiency. On the basis of this information, period prevalences of these complications were calculated. Rates of complications reported by providers in various demographic groups were compared using a Pearson χ² analysis (Minitab, State College, Philadelphia).

Results

During the year before survey completion, the total estimated number of SL wearers evaluated in the practices of 639 study participants was 72,605 (median [IQR] patients per participant: 40 [85]; 25th–75th percentile, 15–100). Practitioner demographic data are presented in Table 1. Patients discontinued SL wear due to corneal complications as follows: 325 patients (0.45%) with MK, 869 patients (1.2%) with corneal edema, 385 patients (0.53%) with corneal neovascularization, and 135 patients (0.20%) with limbal stem cell deficiency.

Table 1.

Demographics of Practitioners^a

	Participants, No.	Patients, No.
Country of residence (n=637)
US	410	49,067
Non-US	227	23,498
Primary practice modality (n=610)
Communityb	472	45,866
Academicc	138	24,919
Level of experience (n=622)
Establishedd	511	60,179
Newe	111	10,612
Practice volume (n=639)
High volumef	320	67,195
Low volumeg	319	5,410

^aParticipants were not required to provide all demographic data; the number of participants who responded to each demographic query are indicated.

^bPrivate, group, or commercial practice.

^cUniversity, academic, or hospital practice.

^dMore than 5 years of experience fitting SLs.

^eFive or fewer years of experience fitting SLs.

^fUpper 50%, based on the reported number of patients evaluated during the previous year.

^gLower 50%, based upon the reported number of patients evaluated during the previous year.

No differences were noted between established and new providers in period prevalence of any complications investigated. Participants who worked in community practices reported higher percentages of patients with MK and corneal edema than their academic counterparts. Non-US practitioners reported higher rates of all complications than US practitioners, and high-volume practitioners (upper 50% by annual patient volume) reported lower rates of complications than low-volume practitioners (lower 50% by annual patient volume). Comparisons between groups of practitioners are summarized in Table 2.

Table 2.

Comparisons of Complications Between Groups of Practitioners^a,b

	Microbial keratitis (n=325), %	Corneal neovascularization (n=385), %	Corneal edema (n=869), %	Limbal stem cell deficiency (n=135), %
Overall	0.45	0.53	1.20	0.20
US	0.38	0.33	1.10	0.12
Non-US	0.60	0.95	1.41	0.32
P value	<.001	<.001	<.001	<.001
Community	0.48	0.56	1.30	0.17
Academic	0.32	0.46	1.00	0.21
P value	.001	.07	.001	.20
Established	0.44	0.52	1.16	0.18
New	0.41	0.55	1.10	0.26
P value	.73	.71	.62	.06
High volume	0.41	0.46	1.11	0.17
Low volume	0.87	1.46	2.24	0.43
P value	<.001	<.001	<.001	<.001

^aOverall and distributed percentages of patients who experienced each complication are presented along with P values (Pearson χ² test) comparing differences between groups. The differences between groups should be interpreted with caution; reported rates of complications are based on recall estimates and not objective clinical diagnosis.

^bData expressed as percentages; P<.05 was considered significant.

Discussion

This study provides preliminary estimates of the percentages of SL wearers who may develop corneal complications. The most common complication reported was corneal edema, which led to discontinued lens wear for 1.2% of patients in this sample. Limbal stem cell deficiency was the least commonly reported complication, occurring in just 0.2% of patients. On the basis of this data, a rough estimate of the incidence of MK in SL wearers is approximately 45 cases/10,000 wearers/year. This incidence is higher than incidence rates reported with both daily wear of either rigid corneal lenses (1.2/10,000 wearers/year) or soft contact lenses (1.9/10,000 wearers/year) and overnight wear of soft contact lenses (19.5/10,000 wearers/year).¹¹ Higher rates of MK in SL wearers than in other contact lens wearers are not surprising given the prevalence of disease in SL wearers, but this finding suggests the need for more rigorous evaluation of risks associated with SL wear.

Standard epidemiologic evaluation of incidence rates for a particular condition requires prospective enrollment of a defined population of patients along with a period of surveillance for the clinical finding of interest. The present study showed that most individual practices evaluate a relatively small number of SL wearers over the course of 1 year. Thus, a classic investigation of incidence would require participation from a large number of practices with an extended follow-up period in order to enroll a sufficient number of patients to provide meaningful results. Both requirements make such a study logistically more challenging than survey-based research and may have contributed to the lack of such a study to date.

The present study relies on estimates of both total number of patients evaluated during the year preceding completion of the survey and the number of patients who experienced SL-related complications during that time period based on the recall of individuals who completed the survey. Health record review was not required, and therefore recall bias may have influenced the results reported. Practitioners may have over- or underestimated the total number of patients evaluated during the year preceding survey completion. An error in either direction would have changed the denominator for all subsequent calculations. Practitioners may have been hesitant to report complications or may have simply not recalled all patients who experienced them. Assuming that practitioners would be more likely to recall more serious complications, the survey intentionally queried estimates of the number of patients for whom complications actually required discontinuation of SL wear. Additional patients may have developed mild corneal complications that did not require discontinuation of SL wear. Variations in practice patterns may exist; one practitioner may have recommended discontinuation of SL wear for a complication of a particular severity, while another practitioner may have managed the complication without instructing the patient to stop wearing their SL. Given these variables, it is difficult to speculate whether data presented represent an over- or underestimation of the true period prevalence of complications in this population.

Caution should be exercised when attempting to draw any conclusions regarding relative risks of complications between different groups of providers. Practitioners who report more complications may simply be more cautious or may be identifying more corneal changes through more detailed examinations than those who report fewer complications. Practitioners with ready access to other colleagues (including corneal specialists) may be more comfortable than more isolated practitioners in observing a new corneal finding than in discontinuing lens wear. Differences in disease severity may also affect the likelihood that lens wear might be discontinued; a patient with very severe disease may continue to wear an SL (with modifications in lens design or wearing schedule) despite corneal changes than a patient with less severe disease who may have alternative therapeutic options. Some practitioners (particularly those who see very high numbers of SL patients) may refer patients back to a general eye care practitioner for ongoing routine care and may therefore not be aware of all complications that could arise for patients for whom they have prescribed SLs. Although differences between groups of providers were noted, observed differences should be viewed with a great deal of circumspection; the study was not designed to define differential rates of complications based on practice location or modality or practitioner experience. Pooling all data to calculate overall period prevalence of the corneal complications evaluated may help to mitigate these potential sources of error; more confidence can be placed in overall estimates of complication rates than in rates reported in subsets of the study population.

The survey did not ask practitioners to provide specific information about patients who developed complications (eg, primary indication for SL wear or details regarding SL design, care products, or wearing schedule). Multiple studies have indicated that most patients who wear SLs do so for the management of either corneal irregularity or ocular surface disease; therefore, it would be reasonable to assume that patients who had complications also had some type of pathologic ocular findings before the initiation of lens wear. In addition to risk factors for complications common to all contact lenses, this underlying pathology may have contributed to the development of complications in patients who wear SLs.

Despite its limitations, this survey-based study does provide an estimate of the frequency with which corneal complications may occur in patients who wear SLs. It also suggests that, whereas the percentage of patients who experienced SL-related complications is low, the risk of MK is greater than for other types of lenses. This information may help practitioners and patients better assess the risks and benefits of SL wear and could provide preliminary data for calculation of the sample size needed for formal investigations of the incidence of complications with this lens modality.

Abbreviations

MK

microbial keratitis

REDCap

Research Electronic Data Capture

SL

scleral lens