Consider 2 approaches when fitting patients.
Scleral lens fitting is a portion of our profession that has seen dramatic increases over the last few years. While scleral lenses date back to the 1800s,1 their current popularity is a fairly new phenomenon.
According to the Scleral Lenses in Current Ophthalmic Practice Evaluation (SCOPE) study, more than 54% of current scleral lens prescribers say they fit their first lens after 2010 and more than 80% after 2005.2
With the increased popularity comes an increased attention by manufacturers to provide better, more reliable products. Today’s labs have the ability to modify lenses on the micron level and alter curves that enable us to adequately fit the most complicated patients. Those patients experiencing mild to severe keratoconus, pellucid marginal degeneration, keratoglobus and even patients suffering from postsurgical complications can find relief where they previously had no other option.3
Unfortunately, the labs do have a limitation. If we are not providing the lab with accurate data, we are possibly hindering their potential for success. Increasing our efficiency with these lenses is crucial and starts at the very beginning.
Accurate selection of your initial lens can go a long way in decreasing unnecessary chair time as well as enhancing the probability of a successful fit. Within this article we will review 2 methods of selecting an initial scleral lens.
You may find practitioners who recommend using keratometry readings as a starting point for scleral lens fitting. However, literature does not typically support this, as the relationship between keratometry and scleral shape is quite weak.4 Scleral lens fitting is based much more on sagittal height and it is difficult to extrapolate cornea values to understand scleral shape.5
Alone, corneal topography is helpful in determining the overall corneal shape and steepest portion of the cornea, but it has its limitations. Corneal topography provides no data on the scleral landing zone.6
A recent study demonstrated that scleral shape is highly asymmetric and that the asymmetry is not often the same amount as found within the corneal toricity.7 This is clear evidence that more information is needed than what our keratometers and corneal topographers are providing.
Understanding the scleral shape is necessary when starting the scleral lens fitting process. Measuring a patient’s side profile without any instrumentation is a skill that I have learned to enhance over the years.
Figure 1. The profile viewing method of scleral lens fitting involves lifting the upper and lower lid and evaluating the overall scleral, allowing for the evaluation of the corneoscleral angle superiorly and inferiorly
This method of profile viewing involves lifting the upper and lower lid and evaluating the overall scleral shape (Figure 1). While this method only allows you to evaluate the corneoscleral angle superiorly and inferiorly, it is an excellent starting point in the absence of other instrumentation.
The theory behind this method is reinforced by a series of studies performed out of Pacific University.8 The studies reviewed the anatomical angles that are formed beyond the limbus. While this review was not inherently designed to support profile viewing, it was one of the first studies to quantify the clear differences within scleral shape. These are the differences that we hope to expose with this method of initial lens selection.
Profile viewing is a skill that we, as eye care practitioners, can learn on our own. This method uses the understanding that we have to take both the cornea and scleral landing zone into consideration when selecting an initial lens.
The first few attempts may require revision in bracketing selections as you place various diagnostic lenses on the patient’s eye. Once you find the correct lens (1 that adequately vaults the steepest portion of the cornea) remove the lens and reevaluate that side profile once again.
Now that the correct sagittal value has been found, take a mental image of what that scleral sagittal value looks like. This will help increase your success rate over time. Efficiency with this method takes a great deal of practice, trial, and error.
One of the major flaws with this method is that it is heavily reliant on the the fitter’s level of expertise. Once you have a lens on an eye, it is up to you to accurately assess your findings and forward that information to the manufacturer.
This becomes increasingly challenging when dealing with conjunctival irregularities such as pinguecula or any type of scleral asymmetry. There is much variability beyond the limbus. A recent study that evaluated this found that the majority of participants, who were prospective scleral lens wearers, were asymmetric or irregular beyond the limbus.8
Figure 2. The profilometry method of receiving topographical data about the sclera holds valuable information for initial lens selection because it instantly provides sagittal height and a detailed description of the sclera.
Profilometry is a method of getting topographical data about the sclera. This holds valuable information for initial lens selection because the sagittal height and a detailed description of the sclera are instantly provided (Figure 2). This instrumentation provides quantitative data points that can guide your process, making initial lens selection seamless.
There are currently 3 instruments available that offer the ability to measure the topography beyond the limbus. Two of the designs are placido disc based. Those instruments include the Eye Surface Profiler (Eaglet) and sMap3D (Visionary Optics). The placido disc instruments require the use of fluorescein for image capture.The third instrument is a rotating Scheimpflug imaging camera called the Pentacam Corneal Scleral Profile (Oculus). This provides thousands of data points covering a range of 18 to 22 mm diameter of the sclera.9,10,11
Figure 3. The Pentacam Corneal Scleral Profile (Oculus) provides a “Projected Final Lens” and “Recommended Trial Lens” using the profilometry data, projecting sagittal heigh and peripheral curves before a lens is placed on the eye. (All images courtesy of Jason E. Compton, OD, FAAO)
Once an image is taken, the software will guide you on the best sagittal height and peripheral curves before any lens is placed on to the eye (Figure 3). If data collection is optimal, trial and error is often not required. Even new fitters can enjoy instant success, as the algorithms are quite effective in finding the correct initial lens.
In addition to accuracy, there are other advantages to profilometry for initial lens selection. These advantages were highlighted during the COVID-19 pandemic, where reusing diagnostic lenses and time spent within the office became real concerns.
With the added accuracy of initial lens selection, practitioners can order lenses completely empirically and perform an over-refraction on a lens designed specifically for a patient. This method also dramatically decreases chair time, as the success rate for these lenses is very high.
An equally important factor in initial lens selection is around the diameter that will be used. Proper diameter selection of the lens speaks to the overall purpose and actual definition of a scleral lens.
The Scleral Lens Education Society recently updated the accepted language for the definition of scleral lenses. Scleral lenses are currently defined as a lens “fitted to vault over the entire cornea, including the limbus, and to land on conjunctiva overlying the sclera.”12
Selecting the correct diameter for your initial scleral lens is a process that can be very straightforward. Once you obtain the horizontal visible iris diameter (HVID) for a patient, adding 5 to 6 mm is sufficient to adequately land a few millimeters beyond the limbus.
Scleral lens fitting can be a rewarding experience for both the practitioner and the patient. While we only discussed 2 methods of selecting an initial lens, other viable options include ocular coherence tomography (OCT)13 and even impression-based models.14
Regardless of the method that you choose for initial lens selection, it is important to take a systematic, evidence-based approach to ensure success. It goes without saying that there is much more to scleral lens fitting than initial lens selection. However, increasing efficiency with this portion of the exam will streamline the process and dramatically increase your success rate.