The exponential growth of scleral lens research in the past five years is evident; the number of scleral lens publications continues to increase, with more than 80 peer-reviewed papers indexed on PubMed in 2020. The International Forum for Scleral Lens Research (IFSLR), whose mission is to advance the discipline of scleral lens prescribing through the coordinated efforts of evidence-based research and clinical practice, hosted its fourth annual meeting in early 2021. This year, the platform was virtual and consisted of three Saturday morning sessions after the conclusion of the Global Specialty Lens Symposium (GSLS) in January. With more than 150 attendees from a diverse international community, the sessions boasted lively panel discussions among the scleral lens researchers and experts. Here, we summarize the research and discussions presented.

SCLERAL LENSES AND IOP

In 2020, we dedicated a small part of the program to scleral lenses and intraocular pressure (IOP); based on the level of interest at that time, we felt it imperative to dedicate an entire session to that topic this year. Several studies of IOP and scleral lens wear were published in 2020, and three of the authors were invited to discuss their research.

Jennifer Fogt, OD, MS, presented data on the methods used to study IOP during scleral lens wear.¹ After sharing data from two of the first modern publications on scleral lenses and IOP,^2,3 she noted that many studies use different methodologies and show different results. This inspired her group to compare two different IOP-measuring instruments: a transpalpebral tonometer and a pneumotonometer. Both instruments were used peripherally over the sclera while a scleral lens was worn.

Twenty patients were randomly assigned to wear 15.2mm- and 18.0mm-diameter scleral lenses for one hour each. During lens wear, peripheral pneumotonometry and transpalpebral tonometry were employed to measure IOP. Those measurements were compared with baseline measurements taken prior to lens application.

The results of this study were conflicting. The transpalpebral tonometer showed a significant change in IOP during lens wear, while the pneumotonometer did not. While this study did not answer the question of whether IOP increases during scleral lens wear, it did confirm that the data collected using different methodologies cannot reasonably be compared. In other words, we cannot jump to conclusions about changes in IOP with a single study or a single instrument.

Gloria Chiu, OD, presented data from a study evaluating IOP in patients who wear scleral lenses and have ocular surface disease.⁴ The researchers retrospectively collected data from examination records of habitual scleral lens wearers. As most studies on this topic are conducted on healthy, normal eyes after only a few hours of lens wear, this study design involving real patients after months of lens wear was a welcome contribution.

Researchers enrolled 25 patients (46 eyes) in this study. Diagnoses included chronic graft-versus-host disease, Stevens-Johnson syndrome, and Sjögren’s disease. The scleral lenses were 17.0mm or 18.0mm in diameter and were custom-ordered and fit for each patient’s eyes. IOP was measured with a Tono-Pen Avia Tonometer (Reichert, Inc.) after lens removal, and central corneal thickness (CCT) was measured by ultrasound.

The results showed a reduction in average IOP after scleral lens wear (–0.89 mmHg), although this was not statistically significant. There was a statistically significant increase of 1.01% in CCT, which was attributed to subclinical hypoxic conditions created by scleral lens wear. This magnitude of swelling is less than the 4% to 6% that is typically considered to be clinically significant.^5,6

Overall, no evidence suggested clinically meaningful changes in IOP or CCT after several months of scleral lens wear by these patients who have ocular surface disease. The measurements taken were representative of the IOP immediately after scleral lens removal but not during scleral lens wear.

The important work of Dr. Fogt and Dr. Chiu led us to wonder about the ability of the available instruments to accurately measure IOP during scleral lens wear. Dan Samaha, OD, pondered this question and redirected the discussion away from evaluating IOP directly. He highlighted the conflicting evidence of IOP studies, indicating that it is not specifically the change in IOP that is concerning but rather the downstream effects at the optic nerve head (ONH).

Dr. Samaha introduced a new approach to evaluating the impact of scleral lenses on IOP by measuring the Bruch’s membrane opening-minimum rim width (BMO-MRW), a sensitive morphological ONH measurement that shows excessive thinning with increasing IOP (Figure 1).^7-9 In the Samaha study, 20 young, healthy participants were recruited to wear scleral lenses. Diurnal changes in BMO-MRW were accounted for before scleral lens fitting, and BMO-MRW measurements were repeated during scleral lens wear.¹⁰

The researchers found that the BMO-MRW decreased after two hours and after six hours of scleral lens wear. After normalizing for diurnal variation, the total BMO-MRW thinning was –3.35µm ± 6.32µm (P < 0.001). Based on calculations made from a non-human primate study, which estimated that the BMO-MRW tends to decrease at a rate of 0.61µm per mmHg,⁹ Dr. Samaha estimates that the mean change of –3.35µm in their study would correlate with an IOP increase of approximately 5 mmHg.

Collectively, these recent studies of IOP suggest that, while the methods and outcomes are variable, there is sufficient evidence that moderate (3 mmHg to 5 mmHg) changes in IOP may be occurring in some scleral lens wearers. Current research is evolving to include more disease populations, which likely will enlighten this issue further. Given current evidence, it is recommended to monitor IOP in all scleral lens wearers, and it is prudent to carefully monitor the ONH in at-risk populations, i.e., in patients who have glaucoma or ocular hypertension.

SCLERAL LENSES IN DISEASE

While the use of scleral lenses is becoming more mainstream,¹¹ this modality remains primarily dedicated to treatment and management of diseases. When scleral lenses are prescribed for disease management, complications related to the disease state will inevitably occur (Figure 2).

The second session of the IFSLR focused on research looking at disease-specific outcomes with scleral lens wear, with presentations from clinical researchers who have recently published papers on this topic.

Daniel G. Fuller, OD, discussed his research on the safety and efficacy of prescribing scleral lenses for patients who have keratoconus.¹² He provided an overview of scleral lenses and keratoconus in the United States and discussed the results of his study.

In 2016, there were an estimated 70,000 scleral lens wearers.¹³ The most common indications for scleral lenses include corneal ectasia (27.5% to 91%)^14-16; postsurgical or posttraumatic corneal irregularity (17.6% to 40.0%)^14,17,18; ocular surface diseases (3% to 49%)^14-16,18,19; aphakia (2% to 23%)^15,16,18; refractive errors (2.6% to 10%),^16,19 and others.²⁰ Reported keratoconus prevalence rates are at least 50 to 265 per 100,000, with an annual incidence of 2 to 13.3 per 100,000.¹² Yet, what is known about the safety and efficacy of scleral lens wear within this group relies on data from earlier polymethyl methacrylate (PMMA) or from first-generation GP lenses and not from contemporary designs.

Dr. Fuller presented data from a retrospective study of patients diagnosed with keratoconus (n = 157 eyes) between 2013 and 2018 who had successfully worn lenses for more than one year. The researchers found that lens-related adverse events were common (55.4% of eyes) but easily managed.¹² Physiological adverse events occurred with a low frequency (9.6% of eyes), seldom resulted in loss of best-corrected visual acuity, and were most often related to disease progression. The significant improvement in best-corrected visual acuity supports the efficacy of scleral lens wear. Robust epidemiological studies are needed for all groups of scleral lens wearers to refine what is known.

Loretta Szczotka-Flynn, OD, PhD, presented a small case series (n = 3) of patients who developed sudden, acute, peripheral corneal edema decades after penetrating keratoplasty for keratoconus.²¹ These patients had relatively low endothelial cell counts but not necessarily below the point at which the cornea will decompensate. In addition, the edema was limited to the peripheral cornea near the interface between the host and donor corneal tissues. Dr. Szczotka-Flynn suggested that this indicated that the acute localized edema was not provoked by a too-low endothelial cell density, which typically leads to a slower, gradual onset of generalized edema. Rather, she suggested that this interesting and, so far, unreported corneal response resulted from mechanical insult to the cornea from less-than-gentle scleral lens applications and removals that created breaks in the host-donor interface. Jan P.G. Bergmanson, OD, PhD, agreed with this assessment. He noted that his histopathological work on radial keratotomy corneas years after the refractive surgery proved that severed stromal collagenous lamellae are unable to heal and that they remain permanently vulnerable to mechanical insult (Figure 2B).²²

Vishakha Thakrar, OD, noted that scleral lenses are commonly used to correct vision of patients who have corneal scarring and irregular astigmatism resulting from previous herpes simplex virus (HSV) and herpes zoster ophthalmicus (HZO) infections. Her report described the development of corneal edema after scleral lens wear in four eyes of four patients who had dormant HSV and HZO keratitis.²³ This is interesting new information, as there appears to be no previously published data on endothelial dysfunction in scleral lens wearers who have a history of HSV/HZO keratitis.

All four patients had a history of endotheliitis secondary to herpetic keratitis. After the scleral lenses were dispensed, all four eyes developed corneal edema within one week to five months of lens wear. In three of the eyes, the clinically significant corneal edema likely occurred because of endothelial dysfunction from prior herpetic endotheliitis. One eye experienced an acute flare up of the herpetic keratitis, resulting in severe corneal edema and subsequent Descemet’s stripping endothelial keratoplasty.

Patients who have a previous history of endotheliitis, as with cases of herpetic eye disease, will likely be more susceptible to corneal hypoxia with scleral lens wear.²⁴ In such cases, an endothelial cell count should be performed to establish scleral lens candidacy prior to prescribing. Frequency of herpetic keratitis recurrences should also be considered prior to fitting scleral lenses.

In summary, experts agree that scleral lenses are remarkable and safe devices for irregular corneas; however, diseases must be carefully monitored, and special considerations should be given to highly diseased corneas such as in eyes that have transplanted corneas and in post-HSV/HZO eyes.

OXYGEN, SCLERAL SHAPE, AND TECHNOLOGY IN SCLERAL RESEARCH

Alejandra Consejo, PhD, MSc, MBA, reviewed an evaluation of the correlation between scleral shape and corneal topographic parameters in patients who have keratoconus.²⁵ Twenty eyes (15 patients) with matching axial lengths and no previous specialty lens wear or ocular surgery were included in this study. Corneal imaging was obtained with the Pentacam HR (Oculus), and three-dimensional corneoscleral maps were acquired using the Eye Surface Profiler (Eaglet Eye). Correlation was noted between flat and steep keratometry values and scleral asymmetry (R > 0.5, P < 0.05). Anterior corneal astigmatism showed poor correlation with the level of scleral irregularity (R = –0.11; P = 0.32). Other disease-specific parameters pertaining to the posterior corneal curvature and corneal thickness were not correlated with scleral asymmetry. The steepest regions of the central cornea, peripheral cornea, and sclera tended to share a common angle (R = 0.92; P < 0.001) for central cornea compared to sclera, but this is not generally the case for the flattest regions, as Figure 3 illustrates.

While it is unclear whether it is possible to predict scleral shape with only a corneal topographer, this technology can provide some indication of the degree of scleral irregularity and the location of the steepest region of the sclera.

James Wolffsohn, BSc (Hons), MBA, PhD, presented an overview of our current understanding of the impact of scleral lens wear on corneal oxygen supply. Theoretical and mathematical models of the scleral lens-fluid reservoir complex suggest that scleral lenses need to be manufactured no more than 250µm thick from materials with a Dk of at least 150 and should be fit with no more than 200µm of clearance.²⁶ Nevertheless, clinical evidence to support these calculations during long-term scleral lens wear is currently lacking.

Dr. Wolffsohn and colleagues examined the effects of eight hours of scleral lens wear on comfort, corneal thickness, fluid reservoir depth, corneal curvature, objective bulbar and limbal redness, corneal biomechanics, and ocular surface oxygen consumption in both eyes of 15 patients.²⁷ All patients were fit with 15.8mm-diameter, 350µm-center-thickness scleral lenses manufactured with materials of 65Dk to 180+Dk. Each lens was worn on a separate occasion, with a minimum of 48 hours between study visits. Corneal thickness and fluid reservoir depth were measured immediately after lens application and again immediately after lens removal eight hours later using the Cirrus OCT (Carl Zeiss Meditec). Additional measurements included corneal curvature, objective bulbar and limbal redness (Oculus Keratograph 5M, Oculus), corneal biomechanics (Ocular Response Analyzer, Reichert), and ocular surface oxygen consumption (Fibox 3; PreSens Precision Sensing GmbH).

All scleral lenses caused stromal thickening after eight hours of wear (+0.75% ± 1.07%) compared to no lens wear (–0.48% ± 1.03%). The 65Dk lens caused significantly more swelling compared to materials of 100+ Dk but had less than 1% difference. Fluid reservoir depth decreased similarly during eight hours of wear (> 100µm settling with all designs), and increased corneal thickness was moderately associated with fluid reservoir depth at application (R = 0.231, P = 0.05). Compared to no scleral lens wear, oxygen depletion was not altered by the 163Dk lens or by the 180+Dk lens. Oxygen consumption was significantly reduced with scleral lenses of ≤ 125Dk.²⁷

David Piñero, OD, PhD, provided an update on various technologies that are currently available for characterizing the corneoscleral topographic profile, including Scheimpflug image-based tomographers, Fourier-domain profilometry, and multiple-gaze profilometry. While all of these technologies provide consistent measurements of the anterior eye shape, they cannot be used interchangeably for clinical purposes.^28,29 They can, however, enable clinicians to characterize the peculiarities of the corneoscleral profile when fitting scleral lenses and thus enable them to achieve a more predictable fitting, particularly in highly irregular corneas.

This work indicates that more scleral asymmetry is present in eyes that have keratoconus and that there is some level of correlation among corneal and scleral data.³⁰ Furthermore, scleral asymmetry is correlated with axial length, and less nasotemporal sagittal height asymmetry was noted in high myopes compared to emmetropes. This observation suggests that profilometry could potentially be useful in monitoring for myopia progression.^31,32,33

The data on scleral shape are increasingly supportive of using scleral topography to define and fit to the unique shapes of eyes wearing scleral lenses. This session reminded us of how we can use technology to understand the ocular surface and the impact of a scleral lens.

JOIN THE DISCUSSION

Collectively, these informative sessions will guide all of us in the fitting and management of these remarkable devices. The fifth annual IFSLR, a live event, is scheduled for Wednesday, Jan. 19, 2022, prior to the 2022 GSLS in Las Vegas. CLS

The authors would like to acknowledge the scleral lens researchers and clinicians who presented at the fourth IFSLR. We also recognize Dr. Lynette Johns for her thoughtful contributions to the IFSLR program and to this article. Support for the fourth IFSLR was provided by CooperVision, Blanchard, and Bausch Health, and we appreciate the educational support from our media partners, Pentavision, LLC and the GSLS.

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