Lente escleral de hoy

Lentes esclerales son ya universales - se utiliza no sólo para los pacientes córnea irregular, pero también para el tratamiento de errores de refracción alto y la presbicia.

Por Gregory W. DeNaeyer, OD

FECHA DE PUBLICACIÓN: JUNIO DE 2012

FECHA DE VENCIMIENTO: 01 DE JUNIO 2015

OBJETIVO DECLARACIÓN:

En este artículo se presentará una actualización de las lentes esclerales actuales y delinear su capacidad para tratar a pacientes con la córnea irregular, los errores de refracción alto y presbicia.

FACULTAD / EDITORIAL BOARD:

Greg W. DeNaeyer, OD

CRÉDITO DECLARACIÓN:

Este curso está aprobado por la COPE durante 1 hora de crédito CE. COPE ID es 34757-CL. Por favor, compruebe su junta estatal de licencias para ver si esta aprobación cuenta para sus requisitos CE para relicencia.

JOINT-SPONSORSHIP STATEMENT:

Este curso de formación continua es conjunta patrocinada por el Colegio de Optometría de Pennsylvania.

DISCLOSURE STATEMENT:

El autor no tiene ninguna relación financiera a revelar.

El reciente resurgimiento de las lentes de contacto esclerales ha mejorado significativamente nuestro éxito en el manejo de pacientes con irregularidad corneal y la enfermedad de la superficie ocular (OSD). 1-4Paciente y la demanda profesional de las lentes de contacto esclerales ha llevado a los fabricantes a mejorar los productos existentes y desarrollar nuevos diseños. Los nuevos

materiales y las soluciones también han contribuido a mejorar el éxito de las lentes de contacto esclerales.

En este artículo revisaremos las últimas actualizaciones en los materiales, soluciones, diseños y técnicas de montaje que se seguirán para promover el éxito de las lentes esclerales.

CLASSIFICATION

The fitting characteristics and functionality of gas-permeable (GP) lenses are directly related to their diameter. Therefore, it's critical that a universal classification system be employed so that practitioners can use designs that have predictive characteristics. The Scleral Lens Education Society (SLS) has recently designed a classification system that defines GP lenses on both size and fitting characteristics (see "Terminology"):^5,6

Corneal lenses (8mm to 12.5mm) are supported completely by the cornea. Corneal contact lenses do not hold a tear reservoir.
Corneal-scleral lenses (12.5mm to 15mm) extend beyond the limbus, and are supported by both corneal and scleral tissue. Corneal-scleral lenses hold a limited tear reservoir.
Scleral lenses (15mm to 25mm) place all lens bearing on the sclera. Scleral lenses are further subdivided as: mini-scleral lenses (15mm to 18mm) which have a somewhat limited tear reservoir capacity, and full scleral lenses (18mm to 25mm) which have an almost unlimited tear reservoir capacity.

This classification system allows manufacturers to design and market scleral lenses for specific types of patients. Practitioners can then utilize these products with predictive results.

MATERIALS

The advent of hyper-Dk materials has significantly reduced hypoxic-related complications associated with scleral lens use. Using materials with Dk values of 100 or more is important with scleral lenses, because they semi-seal to the eye, making tear exchange relatively slow as compared to corneal GP designs. To prevent lens flexure, scleral lenses often are manufactured with thicknesses four times greater than that of corneal GPs. Using hyper-Dk lenses to maximize oxygen helps to compensate for permeability decreases secondary to increased lens thickness.

Occasionally scleral lenses will exhibit poor on-eye wettability (figure 1). If this occurs soon after the lens is dispensed, then it is most likely due to lab-related over-polishing or residual lab debris. Patients who have OSD may also have difficulty wetting a scleral lens secondary to their tear quality. In either case, the wettability can almost always be restored by plasma treating the lens. Instruct the lab to plasma treat each lens ordered and have lenses treated as needed if wettability decreases during the life of the lens.

SOLUTIONS

As with any other type of contact lens, solutions play an important role in the success of scleral contact lens wear. Scleral lenses can be cared for using approved GP lens cleaning and disinfecting products or off-label use of multipurpose soft lens solutions. Using preserved solutions with scleral lenses puts the patient at a greater risk for toxic reactions because residual solution can become trapped underneath the lens, which increases exposure time to the anterior ocular surface. Prescribing a hydrogen peroxide-based care system eliminates exposure to any potential toxins or antigens.

Scleral contact lenses have to be filled with saline before application to prevent trapped air bubbles that compromise both fit and vision. Unfortunately bottled saline solutions contain preservatives that could induce a toxic reaction.

Bottled, non-preserved solutions are available but pose two potential risks. First, there is the possibility of contamination if the bottle is used over several days. Secondly, although non-preserved, most of these solutions still contain a buffering agent that can be toxic to the patient.^7,8

Alternatively you can prescribe off-label use of 0.9% sodium chloride solution that comes in 3ml single-use vials (figure 2). The sodium chloride vials do not contain any buffers and eliminate the risk of contamination because they are single use.

DESIGNS

There has been a dramatic increase in available scleral lens designs in the last five years (see "Scleral Lens Designs"). All of these designs require a diagnostic set for successful lens fitting. Fitting sets generally have diagnostic lenses that have increasing amounts of sag-ittal depth with standard peripheral curves or haptic section.

Determining which lens design to use can be a challenging first step to scleral lens fitting. Visiting with the various manufacturers that are represented as exhibitors at contact lens meetings can be a great way to learn which designs will be most beneficial for your practice.

One of the major differences between available scleral lenses is the amount of customization that can be done on a specific design. Some scleral lenses offer only a limited amount of change that can be made to the standard parameters represented by the diagnostic lens. For the novice scleral lens fitter, this can be somewhat helpful because it can simplify the fitting process. However, some patients may require more creative changes to achieve a successful fit; for these cases, using a lens design that has unlimited customization will be beneficial.

Toric and quadrant-specific design. Most standard manufactured scleral lens designs have spherical front and back surface optic zones. Normally, this design setup fits the patient adequately because the lenses are vaulted completely off the cornea surface; therefore, corneal toricity or irregularity is often not a factor.

Scleral lenses effectively mask both regular and irregular astigmatism by means of liquid reservoir. Residual astigmatic error from a scleral lens correction is often the result of lens flexure that can be eliminated by increasing the center thickness of the lens or improving the lens fit. Occasionally, residual astigmatism can manifest from the crystalline lens and thus is not inherently corrected for by the scleral lens. If the amount of residual astigmatism is significant, the patient can wear glasses over their scleral lenses to correct the astigmatic error. Alternatively, the scleral lens can be manufactured with front surface toricity. In this case, the lens will need to be ballasted to orient and stabilize the lens position.

Typically, scleral lens designs come with a standard spherical back surface haptic. It is now known that the scleral is not spherical, but non-rotationally symmetrical.² Scleral asymmetry worsens with increasing distance from the corneal limbus. Minor differences between the spherical lens haptic and the sclera may be offset due to the spongy scleral conjunctiva.

Some patients have asymmetric scleral anatomy that results in a poor fitting relationship when fit with a scleral lens that has a spherical haptic surface. These poorly fitting lenses often exhibit a with-the-rule appearance. The lens will have 3 o'clock and 9 o'clock compressions, as well as excessive lift at the 6 o'clock and 12 o'clock positions. In these instances, some manufacturers offer toric back surface haptic (peripheral curves), which can dramatically improve the scleral lenses fitting relationship.

Some practitioners report routinely using back surface haptic designs for their scleral lens fits. Esther-Simone Visser, M.Sc., and colleagues reported significant increases in comfort, visual quality and overall satisfaction when patients were switched from back surface spherical designs to back surface toric designs.⁹ Anecdotally, patients with toric back surface haptics report less accumulation of reservoir debris trapped between the lens and the eye during wear.

A few labs are able to manufacture scleral lenses with quadrant-specific curves for either the back surface optical zone or the haptic portion when troubleshooting an extremely complex scleral lens fit. For these cases, optical coherence tomography (OCT) of a diagnostic lens is helpful in determining quadrant-specific changes.

Multifocals. Scleral lenses primary have been used to improve distance vision for patients who have corneal irregularity. Recently, however, there has been some interest in using multifocal scleral lenses to correct presbyopia. Theoretically, multi-focal scleral lenses could be used for patients who have either regular or irregular corneas. Scleral lenses don't translate on the eye, so the available multifocal scleral lens designs incorporate simultaneous designs with center near optics. Unfortunately, multifocal optics may not work well for the irregular corneal patient if they have significant corneal scar tissue or significant residual higher-order aberrations.

NOTCHING LENSES

Scleral GP lenses fit onto the sclera. Scleral GP lenses can fit over mild pinqueculas, but their firm nature prevents them from draping scleral obstacles that have significant elevation. In these cases, a notch can be beveled into the scleral lens so that the lens bypasses the obstacle. Scleral notches can improve the fit for patients who have moderate to severe pinqueculas or conjunctival blebs resulting from trabeculectomy.

A diagnostic lens that is notched can be kept in the office for fitting purposes. Photos of the diagnostic lens can be sent to the lab for evaluation and modification of the notch that will be beveled into the prescribed scleral lens. Notches have to be kept shallow because they will induce bubbles if they are cut too deep. For this reason, it's best to use a corneal-scleral lens or mini-scleral lens because a relatively smaller lens will require a shallower notch.

When the lens is dispensed, we instruct the patient to insert it like a puzzle piece so that the notched area is aligned with the scleral obstacle. At the follow-up visit, monitor the patient to make sure that the lens is still adequately clearing the obstacle and not creating any tissue disruption, which is especially important in the case of conjunctival blebs.

PIGGYBACKING LENSES

For the irregular cornea patient, scleral lenses are considered the lens of choice when all other design modalities have failed. Most of the time, as long as the diameter is large enough, a scleral lens can completely vault up over almost any cornea. There are rare cases where the practitioner will have a difficult time with complete corneal clearance resulting in some areas of lens touch.

If the patient is asymptomatic and their cornea is without any disruption, then lens changes aren't always necessary and the patient can be monitored. However, if the patient is symptomatic--especially if the cornea shows epithelial disruption that is associated with the lens touch--then the practitioner needs to address the fitting relationship immediately.

It is best if the lens vault or design can be changed to improve the fit. If, however, the practitioner is unable to improve the fitting relationship, then a soft lens placed under the scleral lens can be used as a piggyback system. The soft lens effectively cushions the cornea against any scleral lens-related bearing.

If a standard molded design fits on the cornea reasonably well, then start with a daily disposable silicone hydrogel (SiHy) lens that the patient wears underneath the best-fit scleral contact. A daily disposable eliminates the need for multiple solutions and prevents lens-related solution interactions. A SiHy lens will help to maximize oxygen to prevent hypoxic-related complications.

If a standard molded soft lens design does not adequately fit, then a custom fit lathe cut design can be used. Diameters larger than 14.5mm may interfere with the lens haptic to sclera relationship and disrupt the scleral lens fit.

LENS APPLICATION

Scleral lens application is challenging because of the relatively increased overall lens diameter. Patients who are disabled and/or elderly may especially have trouble effectively applying scleral lenses. Dalsey Adaptives, LLC has developed the See-Green device that can be used to help patients successfully apply their scleral contact lenses.¹⁰The See-Green system comes with a stand that holds a lighted plunger (figure 3). Using this system, the patient no longer has to hold the lens, but rather lowers their eye onto it, which leaves both hands free for improved lid control. The light at the center of the plunger is used as a target to allow for central positioning

Scleral lens use has increased exponentially over the last five years. Utilization of scleral lenses has expanded beyond the irregular cornea, as practitioners are now using scleral lenses for patients with high refractive errors and presbyopia. Solution, material and design updates will continue to improve scleral lens fitting success.

REFERENCES

Schornack MM, Patel SV. Scleral lenses in the management of keratoconus. Eye Contact Lens. 2010 Jan;36(1):39-44.
Pecego M, Barnett M, Mannis MJ, Dublin-Johnson B. Jupiter scleral lenses: the UC Davis Eye Center experience. Eye Contact Lens. 2012 May;38(3):179-82.
Schornack MM, Baratz KH, Patel SV, Maguire LJ. Jupiter scleral lenses in the management of chronic graft versus host disease. Eye Contact Lens. 2008 Nov;34(6):302-5.
Jacobs DS, Rosenthal P. Boston scleral lens prosthetic device for treatment of severe dry eye in chronic graft-versus-host disease. Cornea. 2007 Dec;26(10):1195-9.
DeNaeyer G. A New Way To Classify Scleral Contact Lenses. CL Spectrum. 2011 Oct.
van der Worp E. A Guide to Scleral Lens Fitting [monograph online]. Scleral Lens Education Society; 2010. Available at: http://commons.pacificu.edu/mono/4/ (accessed May 2012).
Imavasu M, Hori Y, Cavanagh HD. Effects of multipurpose contact lens care solutions and their ingredients on membrane-associated mucins of human corneal epithelial cells. Eye Contact Lens. 2010 Nov;36(3):361-6.
Gorbet MB, Tanti NC, Jones L, Sheardown H. Corneal epithelial cell biocompatibility to silicone hydrogel and conventional hydrogel contact lens packing solutions. Mol Vis. 2010 Feb 19;16:272-82.
Visser ES, Visser R, van Lier HJ, Otten HM. Modern scleral lenses part II: patient satisfaction. Eye Cont Lens. 2007;33(1):21-5.
The See-Green Lens Inserter. Dalsey Adaptives. Available at: www.dalseyadaptives.com (accessed May 2012).