Scleral Contact Lens Fitting Guide
SCLERAL LENS FITTING
Scleral Contact Lens Fitting Guide
Here is a look at tips for fitting, patient selections, and the benefits of different scleral lens types.
By Jason Jedlicka, OD, FAAO; Lynette K. Johns, OD, FAAO; & Stephen P. Byrnes, OD, FAAO
Dr. Jedlicka is the director of Contact Lens Services at the University of Minnesota Department of Ophthalmology and a partner at Consultative Eye Care, a referral-based practice in Wayzata, Minn. He is a clinical adjunct faculty member at the Pennsylvania College of Optometry and lectures on contact lens and anterior segment-related topics.
Dr. Johns is a clinical associate at the Boston Foundation for Sight and an adjunct clinical faculty member at the New England College of Optometry.
Dr. Byrnes is in private practice in Londonderry, N.H., a former member of the clinical faculty at the New England College of Technology and a consultant for Bausch + Lomb.
Scleral contact lenses may be synonymous with "scary" for some practitioners. The fact is, scleral lenses are much easier to fit than you think. And lenses with larger diameters have their advantages too, such as better fit and more comfort for your patients.
Scleral contact lenses are large-diameter GP lenses with diameters varying from 13mm to more than 20mm. Unlike standard GP lenses, scleral contact lenses completely cover the cornea and extend onto the sclera. Based on diameter, they fall into three categories: corneo-scleral, mini-scleral lenses, and full scleral. Semi-scleral contact lenses are considered corneo-sclerals (Table 1).
Scleral contact lenses may also be defined by their fitting characteristics. Nomenclature for scleral lenses is undergoing development. Discussion over what exactly is a semi-scleral lens, for example, or how to define a corneo-scleral lens is ongoing.
In the following article, three practitioners will discuss the different types of scleral contact lenses and the advantages of the different scleral lens types as well as offer their tips for fitting and troubleshooting.
Corneo-Scleral Lenses (Jason Jedlicka, OD, FAAO)
Unlike corneal lenses, corneo-scleral lenses are fitted to the scleral portion of the eye. They are typically 13.0mm to 15.5mm in diameter, with most less than 15mm. Corneo-scleral lenses are not typically intended to completely vault the cornea (as opposed to most lenses that have a diameter more than 15.5mm, which are). This makes the lenses more inexpensive and easier to work with for patients.
Many corneo-scleral contact lenses are available including but not limited to Semi-scleral 13.5 (ABBA Optical); SO2Clear (Dakota Sciences); Perimeter (Essilor Contact Lenses); and DigiForm (TruForm Optics).
Corneo-scleral lenses may provide better initial comfort, centration, and stability compared to a corneal GP lens for many patients. Nearly anyone who can wear a corneal GP could be wearing a corneo-scleral GP instead. Following a fitting guide, these lenses are easy to fit and inexpensive.
Corneo-scleral lenses are not a good choice for corneas too diseased to bear lens pressure. Given that we rarely see these corneas for a contact lens fitting, corneo-scleral lenses should be a good firstchoice design for most eyes.
Several indications for corneo-sclerals include:
• Any patient who requires the visual correction of a GP lens
• Patients who have not adapted to corneal lens wear or who have problems with lens stability or centration
• Patients who have keratoconus
• Post-PK patients and post-surgical patients
• Patients who have irregular corneas
• Corneas that can tolerate some touch
• Presbyopes with monovision or multifocal designs
Keep in mind that corneo-sclerals are easier for part-time users compared to corneal GPs due to little or no adaptation. The larger diameter means less lid interaction—very little adaptation is necessary.
Fenestrate? Your patient's eye drives the fenestration decision. The fit, more than oxygen or tear exchange, is what counts. Most corneo-scleral contact lenses are available with or without fenestration, which has a significant effect on the fit. Fenestrating will result in a lens that "sits down" onto the eye. No fenestration will allow the lens to "stay up" on the eye. Fenestrations sometime allow bubble formation, but just as often they allow bubbles to escape (Figures 1 through 4). For a non-fenestrated contact lens, tear exchange is achieved through the pump/pressure effect.
Figures 1 through 4. Fenestrations can sometimes allow bubble formation, but just as often they allow bubbles to escape.
The patient's ocular surface condition also plays a role in fenestration. For patients who have a healthy ocular surface, a fenestrated lens permits more fluid and gases to escape while allowing the lens to fit further down on the cornea. Non-fenestrated lenses trap more tears and come in less contact with the cornea, making them a better choice for fragile ocular surfaces.
Fenestrated lenses are more forgiving with lens application—both you and the patient don't need to be as precise. Non-fenestrated lenses need to be applied with fluid while the patient is looking down. Upon dispensing, train the patient to apply scleral lenses with fluid in the bowl of the lens.
Corneo-scleral lenses aren't just for irregular corneas anymore. Standard refractive error patients are excellent scleral candidates. Use these lenses to solve problems with comfort, centration, vision, or stability caused by other GP or even soft lenses.
For patients who have severe corneal pathology, going larger to a mini-scleral or full scleral lens is usually preferred.
Full Scleral Lenses (Lynette K. Johns, OD, FAAO)
Don't be frightened by size when fitting large-diameter scleral lenses. Fitting large-diameter lenses can offer your patients, especially those who have severe ocular disease or ectatic conditions, improved comfort and lens tolerance compared to some smaller diameter lenses. Following are some considerations to keep in mind when fitting these lenses.
Diameter and Fitting Set Constraints When fitting full scleral lenses, diameter is a key parameter. Choosing the best starting diameter for your patient will get easier with time, especially if you have an expanded fitting set with more than one diameter. When you begin with a fitting set that has only one diameter, you'll become very familiar with troubleshooting the lens parameters within that set. Changing the diameter larger or smaller can also help aid your fit for your patients.
I typically start fitting my patients with diagnostic lenses, rather than empirical fitting. It can be intimidating to stray from the parameters outside of the current fitting set when beginning scleral lens fitting. If you don't have a specific diameter available for trial fitting, you may be less likely to design or order a lens outside of the trial lens you are starting with. Remember that you can ask your lab to make lenses in diameters larger or smaller than the lenses you are trialfitting on the patient. I will order lenses 0.5mm larger or smaller than my fitting trial lens diameter—but I find that changes greater than 0.5mm can produce a significantly different fit. You can build your trial set by not returning lenses when changing a fit.
Bearing, Vault, and Sagittal Depth Lens bearing, vault, and/or sagittal depth play an important role in fitting scleral lenses. These fitting considerations are affected by changing the overall diameter. For example, Figure 5 shows the difference in bearing with scleral and mini-scleral lenses. If there was higher sagittal depth, you would see that the vault, or space between the cornea and lens, would increase the amount of the pressure on the haptic and compress the underlying sclera at that area. Compression is lessened if you bear over a larger surface area. This concept comes into play with patients who exhibit a very steep cone, pellucid marginal degeneration, or a prominent graft that requires a deeper sagittal depth. I typically start with a 19mm to 20mm overall diameter to allow bearing over the larger area to support the higher vault and weight distribution.
Figure 5. The difference in bearing with scleral and miniscleral lenses.
Sometimes, steepness in the peripheral cornea can be a challenge to vault with a scleral lens. An example is an ectatic corneal graft in which the graft-host junction is more elevated relative to the center. If you increase the overall sagittal depth, the peripheral cornea can be vaulted using a large-diameter scleral lens. A reverse geometry lens design will also help. Larger diameters help avoid contact with the peripheral cornea by vaulting it and the adjacent sclera, bearing on the peripheral sclera. With a small-diameter lens, the slope of the lens may contact the peripheral cornea, and that can cause mechanical irritation, staining, and neovascularization.
With large-diameter lenses, be mindful of where the edge of the lens will land. Scleral obstacles such as pingueculae, symblephara, scars, and elevations can complicate scleral lens fitting. Lens diameter choice is crucial for patients who have these findings. In the presence of a pinguecula, lens diameters can be smaller to avoid contacting it or larger to slightly compress it. By just abutting the pinguecula, the lens edge can cause inflammation, which may require refitting due to conjunctival hypertrophy with long-term use of a scleral lens (Figure 6).
Figure 6. An example of the scleral lens edge impinging into a pinguecula causing inflammation and hypertrophy.
Increasing the diameter of scleral lenses may help patients who have severe ocular surface disease. Some patients complain of discomfort where the lens is not resting. For example, a patient who had Stevens-Johnson syndrome and wearing a 17mm diameter lens had exposed sclera beyond the lens diameter in primary gaze. I refit this patient into an even larger diameter lens (21mm) for more conjunctival coverage. More coverage protects patients who have ocular surface disease from keratinized lid margins, trichiasis, and severe keratoconjunctivitis sicca.
Scleral Toricity Just like corneal toricity, the sclera can exhibit steep and flat meridians. You can identify scleral toricity meridians by noting compression or impingement of the flat meridian with a spherical lens that is too tight. To identify the steep meridian, look for fluid exchange 90 degrees from the flat meridian. As with corneal toricity, scleral toricity typically exhibits a with-the-rule pattern. Sometimes the only way to identify scleral toricity is to observe the pattern of tear exchange with fluorescein. If there is a path of exchange 180 degrees apart, chances are you've found your steep meridian. Keep in mind that toricity increases peripherally from the limbus, which means the larger the diameter of the lens, the more scleral toricity you will encounter.
You can use the diameter of the lens to your benefit with an eye exhibiting toricity. For example, if the lens has a history of suctioning onto the eye, a larger diameter can help allow more tear exchange and reduce suction. A larger lens will incorporate natural channels with a scleral valley resulting from the steep toric meridian underneath the lens, allowing more fluid exchange to prevent the lens from suctioning.
Alternatively, in the case of too much tear exchange and bubble intrusion, reducing the diameter reduces the amount of scleral toricity encountered in the fit. A smaller diameter lens will likely work much better to prevent excessive tear exchange with debris and bubbles especially if a toric haptic is not available in your lens design.
There are several considerations when deciding between large-diameter versus small-diameter full sclerals. Large diameters offer distribution of lens bearing, support of increased sagittal depth (keratoglobus), support of increased peripheral/ limbal vault (ectatic corneal grafts, elevated graft-host junction, and pellucid and Terrien's marginal degeneration require increased peripheral vault), prevention of lens impingement (pingueculae), protection of ocular surface from microtrauma (keratinized lid margins), and reduced suction and compression complications.
Small diameters decrease the amount of scleral lens haptic toricity and asymmetry; help you avoid scleral lens obstacles (symblepharon, Figure 7); and ease lens application (tarsorrhaphies).
Figure 7. A symblepharon where a smaller lens would be indicated.
Available scleral lenses include Jupiter (MedLens Innovations Inc./Essilor), Tru-Scleral (TruForm Optics), Innovative Sclerals (Innovative Sclerals, Ltd.), Procornea Sclerals (Procornea), Gelflex Sclerals (Gelflex), and Boston Ocular Surface Prosthesis (BOSP, Boston Foundation for Sight), among many other designs.
Fitting Mini-Scleral Lenses (Stephen P. Byrnes, OD, FAAO)
Scleral lenses may be new territory for most contact lens fitters. We are just beginning to discover what tools are available, as well as what challenges may arise and how to solve them. Contact lens fitters need to learn that:
• Sclerals are so comfortable that GP discomfort is likely not a concern.
• Sclerals offer better optics and may be a better choice compared to soft lenses.
• They need to overcome fear of handling a larger lens before they can teach their patients.
All mini-scleral lenses—and all scleral lenses, fit in a similar manner—and fitters are aiming for similar results. Fitters will find variations in lens design and, of course, variations in the result.
Answering the next few questions can help guide your way through fitting scleral lenses.
1. What Am I Trying to Accomplish? To answer this question, evaluate the overall ocular condition and corneal state. Would this eye be better served by fitting, vaulting, or aligning the cornea?
Touching the cornea may result in corneal staining and reshaping/molding. Vaulting the cornea will help protect it. Which lens design will work best on this cornea to clear the limbus and reach the sclera? A corneo-scleral lens will support some of the weight of the lens on the cornea and some on the sclera. A semi-scleral lens will add slightly more weight on the sclera. A mini-scleral lens conveys all weight on the sclera and little to none on the cornea. Increasing lens size gives you more space in the fitting zone over the sclera.
2. Which Lens? Knowing how you want to fit this eye guides your choice. Which will provide the highest rate of success? Keep in mind that, at your request, all lenses can be manufactured with parameters that differ from the fitting set.
For example, with the standard fitting set, the Maxim lens (Accu Lens) will align the peripheral cornea more than the Mini Scleral Design or MSD (Blanchard Contact Lens, Inc.) lens would. The MSD will vault the cornea more than the Jupiter lens would.
3. How Much Control Do I Want? As you gain experience with mini-scleral lenses, you may rely on consultants at one lab more than others. For example, when I fit Jupiter and Maxim I use consultation more than when I fit Blanchard's MSD design. Working with consultants gives you less control of parameter decisions but may bring you to success more quickly.
Using consultation to aid in fitting mini-sclerals doesn't mean that the lenses are difficult to fit or won't work well. All work well—some are better suited to some patients than others, as with all lenses.
Lens Characteristics and Fitting Tips Following is a closer look at a few popular mini-scleral lens designs, including their characteristics and how to fit them.
• Jupiter The Jupiter Lens features a posterior surface which can be manufactured to include reverse geometry, multiple aspheric scleral zones or double slab-off ballasting for stabilization of lens rotation with front toric. The lens is designed to rest upon the sclera and closely contour the cornea.
The ideal fit includes 20 microns of clearance over the entire cornea, increased limbal clearance for a brighter fluorescein layer, and scleral alignment with the edge just above the scleral epithelium.
Three zones are fit with the Jupiter Lens. The corneal zone includes the base curve and first peripheral curve. The limbal zone is the second peripheral curve. The scleral zone consists of the third and fourth peripheral curves.
The Jupiter Lens is manufactured in Tyro 97 (Lagado Corporation) and Boston XO (Bausch + Lomb) materials. The basic trial set includes 14 lenses with differing base curves. Advanced sets are also available that incorporate reverse geometry and advanced keratoconus designs.
Using topographical data, select a base curve equal to the steepest corneal curvature plus 1D when selecting the first diagnostic lens. If reliable corneal topography data is not available, select the 48D lens to start—this will vault most corneas.
Evaluate the three zones of the lens. First evaluate the corneal zone (base curve and first peripheral curve). A scleral lens that is too flat will rest upon the cornea and show central touch. To correct this, choose a steeper base curve. A lens that is too steep will show excessive fluorescein under the central area. Select progressively flatter lenses until any area in the corneal zone almost touches the cornea.
Next, allow the last lens to settle for approximately 20 minutes to allow for conjunctival compression, which could decrease the overall sagittal depth and result in central touch. Reverse geometry lenses may be required to vault midperipheral touch.
• Maxim for Corneal Distortion In an ideal fit, the Maxim lens should align with the cornea or exhibit only minimal bearing (Figure 8). The ideal vault will have 100 microns of clearance over the steepest part of the cornea. No bubbles should be visible under the optical cap (too steep of a sag) or over the limbus (too flat of a sag).
Figure 8. A keratoconic patient wearing a Maxim mini-scleral lens. The lens vaults the superior cornea and aligns to the inferior cornea at the apex of the cone.
A Maxim lens will have very minimal to no movement, and there should be no conjunctival impingement or excessive edge lift. Standard trial lenses are 16.0mm in diameter. Also available are 15.4mm diameter lenses for smaller corneas and 16.4mm diameter lenses for larger corneas.
In the pre-fitting examination, determine flat K and the amount of corneal astigmatism. With corneal topography, note the steepest area on the map and the temporal quadrant. Measure the horizontal visible iris diameter (HVID)—the overall diameter should extend at least 2mm beyond the limbal area of the eye because the Maxim lens needs to bear primarily on the sclera and not the cornea.
In choosing the best base curve for the Maxim, consider the level of corneal distortion. For a moderate cone, try a 7.85mm base curve with a 4.12mm sagittal depth. For an advanced cone, start with a 7.50mm base curve and a 4.62mm sagittal depth. For a sunken post-surgical cornea, try an 8.88mm base curve with a 4.15mm sagittal depth or 8.44mm base curve and 4.42mm sagittal depth. For a bulging post-surgical cornea, start with a 7.50mm base curve with a 4.60mm sagittal depth.
• DigiForm The TruForm Optics DigiForm scleral contact lenses come in five different series: N1 for normal eyes, G1 for post-graft eyes, K1 for keratoconus, L1 for post-LASIK eyes, and RK1 for post-RK eyes. Each series was designed using anterior segment OCT imaging to determine the best fit series of curves for each type of eye, and as such, the best fit lens for each type of eye will usually come from the corresponding fitting set.
The standard diameter is 15.0mm, but it can be made as small as 14.0mm and as large as 16.5mm. Other parameters vary from set to set and are chosen based upon the characteristics of each type of eye.
Begin the fitting process by selecting the lens recommended by the fitting set specific to the lens design you are working with. Fill the lens with saline and fluorescein and apply the lens with the patient's head facing the floor.
You can evaluate the fluid layer between the cornea and the back surface of a semi-scleral or miniscleral lens more easily by adding NaFl to the fluid in the bowl of the lens before application of the lens to the eye (Figure 9). Fluorescein can also be added after the lens is placed on the eye. This is the fluorescein tear flow test. If, after instilling fluorescein on the front surface of the lens, fluorescein shows up in the fluid chamber created by the lens and the cornea, we know that tear exchange occurs with the lens in situ.
Figure 9. Evaluating the fluid layer between the cornea and the back surface of a DigiForm Lens.
After waiting to evaluate the fit, you should find a lens with a broad area of slight apical clearance, scleral alignment, and minimal edge clearance. The DigiForm series is intended for a lower degree of vault than some other mini-scleral lenses, and it may even exhibit minimal touch in places. This is due to the fact that each series is intended to fit the specific eye shape it is fitted to, so the degree of vault should be fairly even across the corneal surface. You can order the DigiForm lens with or without fenestration and adjust the parameters (diameter, midperipheral curves, optic zone size, etc.) as desired with little restriction.
• MSD This lens design incorporates a reverse geometry curve-based system to allow for easy manipulation of parameters in optimizing fit (Figure 10). The fitting guide is based on sagittal depth (SAG) as the initial fit parameter with the midperipheral vault as the other variable. Using a simplified fitting process, the MSD lens design can usually be made to fit nearly any eye shape by just adjusting these two parameters. It's available in two diameters, 15.8mm and 18.0mm.
Figure 10. An MSD lens on a keratoconic cornea. This illustrates the extreme clearances that occur when fitting mini-scleral lenses to a highly irregular cornea.
Fitting sets are available fenestrated and non-fenestrated. The non-fenestrated set has 30 lenses including SAGs of 3.60mm to 5.80mm in 0.2mm increments, while the fenestrated sets include 36 lenses with SAGs ranging from 3.70mm to 4.80mm in 0.1mm steps. Each SAG value has three profile curve options: standard, increased vault, or decreased vault. Beyond the fitting set, the lenses are available in both non-fenestrated and fenestrated designs of 15.8mm and 18.0mm from a SAG of 3.60mm to 5.80mm in 0.1mm steps, in vaults that also include a double increased and double decreased vault as well as a standard or flat edge profile.
To begin the fit, the fitting guide will suggest a SAG based on the type of eye being fit. Fill the lens with saline, add fluorescein, and place the lens on the eye with the patient in a face down posture. It should exhibit clearance over the entire cornea and limbus (Figure 11). If you can't obtain central clearance, move to a deeper SAG. If there is clearly too much central clearance, choose a shallower SAG.
Figure 11. MSD lens on an irregular cornea. This lens demonstrates the scleral fitting zone.
Once you obtain the ideal clearance, inspect the midperiphery of the lens. If you see too much or too little clearance in this region, simply change the vault to increase or decrease this clearance.
Finally, when you determine the proper SAG and vault, monitor the edge for compression. Too much compression means that the edge may need to be flattened. CLS
Contact Lens Spectrum, Issue: October 2010