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What Solution is to Be Used for Scleral Lenses?

Ralph P Stone and William J Benjamin

Disclosure

Consultant to Alcon Laboratories,

NovaBay

Pharmaceuticals

Stock in Merck

Proprietary interest in SMM Ventures, LLC

Have proprietary interest in Scleral solution discussed in this talk

Scleral Lenses—A Different World

Often used on the “difficult” that can be diseased or compromised corneas

Uses lens materials originally used for small rigid lenses with lots of movement on the eye to allow tear exchange

Lens designed to trap a lot of “stuff” under the lens

Exchanges tears at best less than a soft lens and often after hours of wear

And we use solutions designed for inhalation therapy to fill the void under the lens.

Improving wear of Scleral lenses

We have improved the materials with high

Dk

rigid materials.

We have improved the lens designed with options to diameter, options in designs of the scleral landing zones.

But we have done little to improve the solution used with the lenses.

Improving wear of Scleral lenses

We have improved the materials with high

Dk

rigid materials.

We have improved the lens designed with options to diameter, options in designs of the scleral landing zones.

But we have done

little

nothing to improve the solution used with the lenses.

What are the solution issues?

The post lens tear film!

A rigid lens has a POLTF thickness of approximately 30um

1

A soft

c

ontact lens has POLTF of an average of 2.34 um.

1

The scleral

lens has

a

POLTF thickness

often exceeding 250um

The liquid under the lens can have a significant effect the corneal environment.

JJ Nichols, PE

Kingsmith

. Thickness of the pre- and post—contact lens tear film measured in vivo by interferometry. IOVS 2003; 44(1):68-77

What do we see?

Evidence of hypoxia even with high Dk materials1The Scleral lens should “semiseal” to the eye without movement to hold a fluid reservoir2The fogging/clouding3, reservoir debris2, tear debris under the lensVisser 4 found the that 48.7% of patients with scleral lenses (>18mm) needed to remove and refill the reservoir at least once during wear. Caroline and Andre2 estmated that 1 in 5 patients some evidence of clouding (or haze).

1. Michaud et al. CLAE 2012; 35(6):266-71 2. W

DeNaeyer

, CL Spectrum June 2010 3. P Caroline, M Andre CL Spectrum June 2012; 27: 56. 4.E-S

Visser

et al Modern Contact Lenses parts I and II, ECL 2007; 33(1): 13-20 and 21-25.

Building a hypothesis for improvement

Laboratory analysis of the reservoir clouding by Walker and co-workers found evidence of mucin, lipids (meibom) and proteins1.Work by Bachman and Wilson indicate that the composition of the bathing solution has a significant effect on the sloughing of corneal epithelial cells as measured by specular microscopy.2The balance of Na, K, Ca Mg have effects on corneal sloughing.

1. M Walker et al, Laboratory analysis of Scleral lens Tear Reservoir Clouding, GSCLS Poster 2014. 2. WG Bachman and G Wilson, Essential ions for management of the Corneal epithelial Surface, IOVS 1985; 26:1484-88

Hypothesis

Using saline based on NaCl alone may increase the loss of corneal cells.Therefore the use of inhalation saline may not provide a desirable environment under a scleral lensNot much is known about the effect of pH and maintaining pH at known tear levels with buffers is desirableOsmolarity may also be important. Although there are few reports of corneal edema, but these have been primarily attributed to the thickness of the lens and tear reservoir.1 But we also see lens settling reducing the tear vault by as much as 70um. Is It all settling? Could it contain a component of edema from fluid absorption of the insertion solution.

1. L. Michaud et al. CLAE 2012; 35(6): 266-71

The Test

Four formulations

All balanced to tear concentrations of sodium, potassium, calcium and magnesium

All phosphate buffered at 7.4

Two with added wetting agent

Varying in

osmolarity

301

mosm

320

mosm

330

mosm

346

mosm

The Human Experience

A single patient with

keratoconus

who reported to have significant hazing requiring as many a

3-4

removals per day

and reinsertions using inhalation saline

. Increased in frequency as the day progressed.

Used each solution for 3 days.

Reported hazing, overall comfort over the course of the day

Results

Patient reported no more than one reinsertion per day for hazing only after 7-9 hours of wear.

Lenses were reported comfortable throughout the day.

Lens wearing time was within or better than the usual schedule for the individual

No significant difference in any parameter related to

osmolarity

What’s Next

Larger 1 month clinical with variety of patients using 2 formulations

Both balance with essential ions and phosphate buffered

pH= 7.4

Osmolality at 315-320

mosm

Different in the addition of a wetting agent

Conclusion

The literature and anecdotal results indicate we are using the wrong solution for inserting scleral lenses.

The right solution may make scleral lenses a choice for a variety of patients including

normals

.