The Effect of a Scleral Lens on the Anterior Chamber Depth and Minimum Rim Width

Study Overview
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Brief Summary
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The purpose of this study is to evaluate the use of two instruments to measure changes in two ocular structures: 1) the anterior chamber depth (ACD) - measured using low coherence optical biometry, and 2) minimum rim width of the optic nerve head (MRW) - measured using optical coherence tomography. Changes in these ocular structures indicate fluctuations in intraocular pressure (IOP) and will be measured during scleral contact lens (SGP) wear to determine if SGP wear influences IOP. We hypothesize that a scleral lens increases the intraocular pressure (IOP) during active wear and that the ACD and MRW will also change.

Detailed Description
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Contact lenses are often used to correct vision blur. The most common types of contact lenses include those referred to as 'soft' and 'rigid'. Visual acuity through rigid lenses often surpasses that of soft lenses. Historically, these lenses have been small in diameter, and hence patients also felt discomfort when wearing the lenses. Scleral lenses are relatively new, customized devices that have gained popularity with patients and practitioners in the past 5-10 years, because they are more comfortable and provide more stable vision than the small diameter rigid contact lenses. However, relatively little is known about the physiologic response of the eye to the scleral lens, or the long-term effects of their use, since they are such a new modality. Maintaining the IOP within the eye is imperative to prevent damage to ocular tissue, which can occur in glaucoma. Given the landing of scleral lens overlying the sclera and ciliary body, which assist in modulating the transport of fluid in the eye, there is a potential for these lenses to impinge on fluid drainage which could lead to increases of IOP during scleral lens wear. The placement of the lens creates an obstacle in evaluating IOP while the lens is actually on the eye (covering the cornea), and since increases in IOP may only occur during lens wear, which is removed when determining clinical IOP measurements, it is difficult to monitor IOP during scleral lens wear with traditional IOP instrumentation (ie. iCare, Goldman, etc). Optical coherence tomography is a non-invasive imaging technology that has revolutionized how the retina and optic nerve are clinically evaluated. The optic nerve head is typically assessed using radial scans, from which the minimal distance from the Bruch's membrane opening to the inner limiting lamina is quantified as the minimum rim width (MRW). With changes in IOP, the MRW is known to also change in thickness. Many studies are investigating the MRW changes during IOP fluctuations, with studies finding a decrease in MRW during acute IOP increase. In this project, MRW will be used to indirectly assess changes in IOP by measuring the MRW periodically during active scleral lens wear. In addition, we are incorporating low coherence optical biometry (Lenstar) to evaluate the effect of the scleral lens pressure on the anterior chamber. Using the Lenstar, corneal thickness, anterior chamber depth (ACD), lens thickness and vitreous chamber depth can be quantified. In this project, ACD will be used to indirectly evaluate changes in the pressure within the anterior chamber. The assumption is that the ACD will change based on changes in pressure in the scleral lens tear reservoir. This study will add to the knowledge of how the scleral lens affects the dynamic pressure system of the eye. Based on the implications for disease with chronic increases and fluctuations in IOP, this is important information to understand with the scleral lens, a relatively new refractive treatment modality.

Official Title
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The Effect of a Scleral Lens on the Anterior Chamber Depth and Minimum Rim Width

Conditions
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Ocular Hypertension

Intervention / Treatment
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* Device: Scleral Lens
* Other: No lens


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: young, normal individuals Exclusion Criteria: IOP > 20mm in either eye, and h/o ocular hypertension, glaucoma, or ocular surgery that can affect IOP. h/o scleral lens wear or current scleral lens wear

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 60 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Single Group Assignment
Interventional Model Description: Subjects are all non-scleral lens wearers. One eye (test) will be selected to wear a scleral lens, and the contralateral eye (control) will not wear any lens.
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Experimental: Scleral Lens<br>One eye will be randomly selected to wear a scleral lens for a 6-hour testing period. | Device: Scleral Lens<br>* The contact lens will be worn on one eye.<br>|
| Active Comparator: Control: no lens<br>The contralateral eye will not wear a lens. | Other: No lens<br>* No lens worn on the contralateral control eye<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Change in minimum rim width from baseline to 6-hours SL wear | The Bruch's membrane opening to the inner limiting lamina (termed the minimum rim width) will be measured at the optic nerve head. | at baseline, after 2-hours lens wear, and after 6-hours lens wear | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Intraocular pressure (IOP) | IOP will be measured using the Diaton and iCare tonometers | at baseline, after 2-hours lens wear, and after 6-hours lens wear | 
| Anterior Chamber Depth (ACD) | ACD will be measured with the Lenstar A-scan | at baseline, after 2-hours lens wear, and after 6-hours lens wear |