Scleral and conjunctival elevations can present a real challenge to the scleral lens fitter. When a lens lands on a focal elevation, it can cause discomfort, redness, and instability, and debris can accumulate under the lens as it passes through the channel created by the lens sitting on the obstacle. Fortunately, we have several design options to circumvent these elevations and provide an optimal fit in the presence of an obstacle.
Some of the more common elevations found in the zone of the eye where a scleral lens might land include: pingueculae, scarring from prior injury or surgery, pterygia, filtering blebs, or tube shunts. These elevations can be found in a wide variety of heights, widths, and locations.
A scleral lens that compresses a pinguecula, pterygium, or scar tissue can cause a patient to be dissatisfied, while a lens that compresses a filtering bleb or tube shunt can have serious health consequences and needs to be carefully monitored even when design adjustments are made.
There are essentially 4 ways to modify a scleral lens to accommodate an obstacle in the landing zone:
- Adjust the overall diameter to avoid the obstacle completely
- Notch the lens edge to fit around the obstacle
- Add a focal area of vault to go over the obstacle
- Impression-fit the lens to conform to the scleral lens shape and contour, including the obstacle itself.
Choosing the best method depends on the obstacle itself, the unique attributes of the individual eye (obstacle notwithstanding), and lens cost factors. This article discusses each of these methods for working with obstacles, when to choose each method, and how to order the necessary modifications.
Changing the Diameter
Changing the diameter of a scleral lens to avoid a scleral obstacle typically means choosing a smaller overall diameter, although in some circumstances, a larger diameter may be an option, as I will discuss later.
Going smaller is most effective when the obstacle is far enough out to pull in the landing zone (Figure 1) while maintaining corneal and limbal clearance and providing an adequate surface area for landing. The closer an elevation is to the limbus, the less likely this strategy will be effective.
Going smaller in overall diameter is not always simply a matter of making a lens smaller. Nonspecifically decreasing the diameter of a scleral lens may mean that all aspects of the lens shrink in size. This may lead to an altered fit over the cornea and the limbus, which could cause inadequate limbal clearance and a host of other issues. When going smaller, clearly specify to the lab that you want to decrease the width of the curves in the scleral alignment zone only; otherwise, switch to a different design that is made to fit with narrower alignment in the first place (Figures 2 and 3).
Increasing lens diameter may also be effective for managing scleral obstacles, provided the obstacle is relatively shallow and close to the limbus. In these instances, going to a full scleral — one that fully covers the obstacle and extends beyond it — can work as well (Figure 4). Keep in mind that this is possible only if the lesion is shallow enough that it does not cause the edge to lift off and if the eye does not react negatively to the pressure of the lens on the lesion.
Notching and Vaulting
Notching has been the traditional means of dealing with scleral obstacles and is still widely used. A notch is simply a region of the lens edge that is cut out to accommodate a scleral obstacle (Figure 5). In many instances, particularly in eyes after glaucoma surgery, notches may still be preferred. Because they don’t ride on top of the elevation, notched lenses will be less likely to affect the function of a pressure-lowering bleb or shunt.
Notching offers some benefits over other alternatives. It can allow a larger lens to be fitted, if needed, while still accommodating an obstacle. It will fit around an elevation when a smaller-diameter lens is not an option or will not fully avoid compression of the bump. It is possible to make minor modifications to the notch, either in the office or by the manufacturer, without having to remake the lens from scratch.
On the other hand, notching a lens may have some drawbacks. A notch that is too large from the outset cannot be adjusted, and the lens will need to be remade. A notch that is too large or needs to navigate an obstacle that is near the limbus may not form a proper seal to the sclera and may allow entry of debris or even cause air bubbles. In some cases, a notch can create lens awareness that affects a patient’s comfort and wearing time.
Vaulting a scleral obstacle is a newer means of management. A vault, also known as a microvault, edge vault, or edge lift, is a localized rise in the landing zone of a scleral lens to form-fit over the scleral elevation (Figure 6). This works much like notching, but instead of removing part of the lens edge, the edge contours the bump and covers some or all of it. Again, in cases where the area under the vault may be affected by pressure, such as a filtering bleb, the lens must not rest with too much weight on the obstacle. Also, there are limitations to how deep a vault can be made, and in instances when the obstacle is too elevated, a vault will not be a viable option.
Vaulting a scleral lens over an obstacle has several benefits. For example, the vault can shelter and shield the area of elevation. In the presence of a pinguecula, scar tissue, or a pterygium, this can be desirable as it protects these areas from the elements and may help slow progression or even improve the problem area. Vaulting also reduces the risk of some of the negatives of notching; by extending to the edge of the lens, there is less risk of bubbles, debris, and lens awareness. The decision to notch or vault comes down to the individual circumstances and which is more appropriate for the eye being fitted.
Designing a Scleral Lens Notch
There are several approaches to notching a scleral lens. Because the notch does not have a specified height or elevation, the only necessary information is the location, the width of the notch along the lens edge, and how deep into the lens the notch must extend. The lens does need to be rotationally stabilized and will require either front surface stabilization or back surface toricity that aligns to the scleral shape. One method of doing this is to design and order a lens for a patient, dispense it, allow it to stabilize, then mark the lens with a permanent marker to designate where the notch must be placed (Figure 7). From there, you can create the notch yourself if you are daring and have a rotary tool, or you can return the lens to the lab for notching.
Another method for notching a scleral lens uses photography. Sending a photo of the lens on the eye to the fabricating lab will give them an idea of the size and location of the notch. Again, this is best done with a lens that is already fitted and functioning well or with a trial lens that has stabilized and is settled into position. Having some type of grid or markings overlay the photo can also help the lab get an idea of the true size of the notch needed.
A more advanced technique for notching a scleral lens is to use scleral lens topography. Scleral topography can indicate the notch location and size (Figure 8), designate the cutout region (Figure 9), and help locate the scleral toricity for back-surface stabilization of the lens. In addition, using the tools within the software enables practitioners to better approximate the rest of the fit, taking into account the loss of lens-edge elevation that will occur when the notch is created. (For more information on corneoscleral topography, see page 28.)
A well-designed notch should fairly contour the scleral obstacle, avoiding bubble formation and undue lens awareness, and not aggravating the obstacle itself (Figure 10). Keep in mind that a scleral elevation will lift the edge of the lens and create extra central clearance. When a notch is added, you should expect to lose a considerable amount of central clearance; increasing the overall lens sagittal depth will be necessary to compensate. The amount varies depending on the height of the elevation but can exceed 100 microns.
Designing an Edge Vault
Designing an edge vault, or microvault, is similar to designing a notch with one exception, the height of the vault also must be specified. An edge vault will be more precisely designed than a notch, and, therefore, more precise measurements are helpful, although the bulbar conjunctiva is quite forgiving.
To design a microvault, fit a lens with some form of back- or front-surface stabilization. Once the lens is properly fitted and settled into position, precisely mark the lens or photograph it in position. Using the slit lamp, rotate an optic section or parallelepiped into position and note the exact location of the apex of the obstacle in degrees (0 to 360 degrees). Measure the apex in relation to the edge of the lens (i.e., at the lens edge, 0.25 mm outside of the lens edge, 0.50 mm inside of the lens edge); this will allow proper placement of the highest point of the vault (Figure 11). Next, measure the width of the obstacle along the lens edge, as this will designate where the vault will begin and where it will end. Finally, estimate the height of the obstacle. Most scleral obstacles are at least 200 microns in elevation, so for an average obstacle, starting at 200 to 250 microns may be reasonable, whereas for obviously larger bumps or blebs, starting at 350 to 400 microns might be more appropriate (Figure 12). This will have to be estimated unless scleral topography is available to make this measurement.
The use of scleral topography can also aid in microvault design. The scleral map will show the precise location of the elevation; the height of the obstacle can be measured using the software tools. In Figure 13, the pinguecula can be seen clearly in the nasal sector of the eye. The lens fitted was 16 mm. At the 16-mm edge location, the axis, decentration, and width can be measured. The height of the pinguecula at the lens edge was +127 microns, while the sclera outside the area of the 3-mm microvault zone was –80 microns, indicating that a microvault of roughly 200 to 225 microns in depth would be appropriate.
Microvaults can also be added to a lens inside the edge and fully enclosed by the landing zone when necessary. This can be helpful when a larger lens is desirable but the obstacle is too deep and compression of the elevation causes symptoms (Figure 14). Designed and ordered in the same manner as a vault at the lens edge, the vault located inside the scleral zone is another option for managing irregularities in the scleral contour.
Impression Scleral Lenses for Obstacles
Another method for accommodating scleral obstacles is through the use of impression-guided freeform lenses. An impression of the ocular surface detects all scleral elevations and depressions. This impression guides the fabrication of a lens that will match the ocular surface, accounting for all irregularities. This method is easiest for the practitioner as it requires no extra effort beyond the basic impression process. It also most closely matches the eye shape to accommodate obstacles, yielding the best possible result, particularly with complex obstacles. The only drawback to this method is the cost. Impression-guided freeform lenses are significantly more expensive than standard lens designs for patients and practitioners.
Scleral obstacles can add a layer of challenge to scleral lens fitting, but with modern lens design options that continue to expand, the scleral lens practitioner has increasing ability to properly manage patients with these complexities. Understanding how to go about prescribing lenses with edge modifications that compensate for scleral elevations can open the door to utilization of these tools and not having to settle for a substandard fit. This will result in greater patient satisfaction and optimal outcomes.