Fitting Scleral Lenses in Keratoconus Patients
Fitting Scleral Lenses in Keratoconus Patients
A look at different scleral lens designs, fitting techniques, and troubleshooting tips.
By James S. Li, OD
Larger-diameter contact lenses such as scleral and mini-scleral lens designs are becoming more popular among practitioners fitting patients who have various corneal ectasias. These lenses are great tools to provide relief for patients who have been exceedingly uncomfortable with corneal contact lenses, and they can often help postpone or eliminate the need for a penetrating keratoplasty.
Traditionally, patients fit with larger-diameter contact lenses are those who have previously failed in other lens designs, including soft, rigid corneal, piggyback, and hybrid lenses. Discomfort with corneal GP lenses is usually caused by the interaction between the irregular corneal surface and the lens, as well as the movement of the lens and its interaction with the lids during blinking. Scleral lenses usually eliminate this discomfort because they are typically fit with complete corneal clearance and only scleral bearing, while their large size ensures that there is minimal eyelid interaction.
Scleral lenses are not new. Leonardo da Vinci was the first to conceptualize and create sketches of a lens placed directly on the eye that could aid with vision. In the 19th century, a British astronomer, Sir John Herschel, proposed the idea of correcting vision with a combination of a corneal mold and jelly-filled capsule.
Adolph Eugen Fick in 1888 took Herschel's ideas and created the first scleral contact lens. Unfortunately, these lenses were made entirely of glass and could only be tolerated for a few hours of wear time.
Dr. William Feinbloom, an optometrist from New York, then used polymethylmethacrylate (PMMA) to fashion scleral lenses. While an improvement over glass lenses, the poor oxygen permeability of PMMA resulted in complications such as neovascularization of the cornea and microcystic corneal epithelial edema that continued to make scleral lenses an unsuitable visual aid.
With the invention of GP materials in the 1970s, Dr. Donald Ezekiel in 1983 was able to fabricate these new materials into scleral lenses. However, failures were still common due to poor lens design, which resulted in excessive scleral compression, bulbar conjunctival congestion, and chemosis. The introduction of GP materials was revolutionary for scleral lenses and has led to the development of new and much improved lens designs being utilized today.
The uniqueness of scleral and mini-scleral lenses over corneal, corneo-scleral, and semi-scleral lenses is that their optimal fit demonstrates complete corneal clearance with scleral bearing. Complete corneal clearance reduces the risk of further corneal compromise caused by corneal bearing from traditional or standard corneal lenses. Large-diameter lenses are also a great tool in masking corneal irregularity that results from various corneal ectasias—especially for patients who have failed in traditional corneal, piggyback, or hybrid lens fits. It also provides an alternative vision solution for those who have grown intolerant to corneal lenses or for patients who have high amounts of residual corneal astigmatism.
Mini-Scleral Versus Scleral Lenses
Just like with fitting corneal GP lenses, the primary decision is which diameter to fit. Mini-scleral lenses have a diameter range of 15mm to 18mm in size, while scleral lenses range from 18.1mm to 24mm (Scleral Lens Education Society Web site). The scleral and mini-scleral lenses contain three zones: the optic, transitional, and haptic zone. Because of the way these lenses fit, the optic zone between the base curve of the lens and the cornea contains a space filled with liquid (tears), which provides a nearly perfect refracting surface. The haptic zone is the area that rests on the sclera itself, with the transitional zone in between these two zones.
Mini-scleral lenses function much like scleral lenses do; the smaller diameter results from a smaller peripheral or haptic zone, which offers both advantages and disadvantages. With a smaller peripheral zone, the distribution of the lens weights rests on a smaller area of the scleral surface, which may cause more scleral compression. Because scleral surfaces become more circumferentially uniform toward the limbus, a mini-scleral design, if not properly fit, may cause negative pressure to build up behind the lens with each blink, resulting in a plunger-like effect on the lens itself. This can result in limbal vascular engorgement and chemosis, and will eventually lead to corneal edema.
The goal of both mini-scleral and scleral lenses is to provide the support necessary for the increased sagittal depth, including limbal and peripheral vault. This is useful in more advanced cases of keratoconus, keratoglobus, and other corneal ectasias. Additional limbal and peripheral vaulting avoids sutures in penetrating keratoplasties and conjunctival growths close to the cornea.
Fitting these larger-diameter lenses is based not on corneal topography and keratometry, but on sagittal depth. The most important tools are fluorescein, unpreserved saline, a slit lamp, and a trial fitting set. A fitting set will eliminate the need for multiple trial lenses, which can make the fitting process more frustrating for both practitioner and patient. Knowing the design of your chosen scleral lens is important, especially when examining fluorescein patterns. This combination will allow you to properly troubleshoot problems that may occur with the lenses. Each trial lens set has its own method of fitting; the techniques discussed here are specific to the Jupiter Lens by Visionary Optics (formerly MedLens Innovations) and the MSD lens by Blanchard. Essilor also manufactures the Jupiter lens, but secondary to software translation it is recommended to order the lens from the company that supplied the diagnostic set.
Jupiter Mini-Scleral and Scleral Lenses
The typical Jupiter scleral lens has two design categories: mini-scleral and scleral. Within each are three different profiles: the Jupiter Standard, Jupiter Advanced Keratoconic, and Jupiter Reverse Geometry designs. Each design is used for different degrees of corneal ectasias. However, the profile most commonly used is the Jupiter Standard. Each design has a base curve and four peripheral curves that are divided into three different zones: the corneal zone, limbal zone, and scleral zone. The corneal zone, which includes the base curve and one peripheral curve, contains aspheric optics to diminish spherical aberration. The limbal zone is characterized by the second peripheral curve, with the scleral zone represented by the third and fourth peripheral curves.
Visionary Optics recommends fitting Jupiter lenses based on the Vault Reduction Method (VRM). To start, the company recommends taking the steepest corneal curve obtained through keratometry or corneal topography and adding 1.00D. The ideal fit should be steep enough to rest on the sclera and completely vault the cornea. The base curve is then reduced progressively as necessary until the lens almost touches the cornea. This is considered the ideal central fit.
The MSD lens design includes two different diameters: 15.8mm and the recently released 18.0mm lenses. These lenses are fit purely by sagittal depth, making keratometry unnecessary. Blanchard recommends a starting sagittal depth value for the initial lens that is based on the irregularity of the cornea (Table 1). Usually, for limbal zone clearance, Blanchard recommends starting with its standard limbal zone clearance, and based on fit, you must decide whether more or less limbal zone clearance is necessary for complete vault.
The MSD fitting set comes with a decreased, standard, and increased limbal zone clearance, but can be ordered with a double increased limbal zone clearance if necessary. Although the fitting set contains only one type of edge clearance (scleral curve(, practitioners can order one or two steps flatter to promote tear exchange and avoid lens impingement.
Evaluating the Fit
Begin by filling up the scleral lens with unpreserved saline and dip a fluorescein strip into the saline to create a fluorescein cocktail. The easiest method of application is to position the lens on a large DMV plunger and have the patient open his eyes wide while looking down into a mirror. Hold the eye open with one hand to prevent blinking and bring the scleral lens toward the eye with the other hand. This technique helps to maintain as much of the fluores-cein cocktail inside of the lens as possible while minimizing insertion bubbles that may impair the fit evaluation. Once the lens is properly applied, view the lens with diffuse light using the slit lamp to ensure that there are no areas of corneal bearing or any air bubbles. If you observe a large central bubble, the lens may be too steep or have too much sagittal depth. Conversely, if you see central bearing, the lens may be too flat or have too little sagittal depth.
Once you observe a uniform central pattern, evaluate the tear layer thickness to determine the amount of corneal clearance. Focusing on the front of the scleral lens using an optic section should show four distinct bands. The first bright band is the front of the lens; the second dark band is the lens itself; the green band is the tear layer; and the last thick band is the cornea (Figure 1). You can estimate the thickness of the tear layer by comparing its thickness to that of the cornea, which is typically between 400 microns to 500 microns thick. A tear layers of 200 microns to 600 microns is desirable in the central corneal zone.
Figure 1. Reading the tear layer.
Evaluate the limbal zone next. The limbus contains important stem cells, and bearing at the limbal zone should be avoided. The stem cells act as a barrier to conjunctival epithelial cells, and bearing can result in damage. A stem cell deficiency can result in conjunctivalization of the cornea, including vascularization and appearance of goblet cells, which ultimately results in an unstable and irregular corneal epithelium. If you observe limbal bearing, increasing the limbal zone clearance in the MSD lens or steepening the second peripheral curve on the Jupiter lens will resolve this. In the limbal zone, a tear layer of 100 microns around the entire limbus is ideal.
Lastly, evaluate the scleral zone. This should be the only area where the scleral lens shows bearing on the eye. Unlike other lenses, with a scleral lens, little to no movement is desired, but it is important to make sure some tear exchange is present. If you observe excessive edge lift, increasing the sagittal depth of the MSD lens or steepening the third and fourth peripheral curves on a Jupiter lens will amend this. If scleral impingement or blanching of conjunctival blood vessels is visible, both MSD and Jupiter lenses have the option of flatter scleral peripheral curves.
Once a suitable initial fit is achieved, evaluate the fit after 20 to 30 minutes of wear time. This allows the scleral lens to settle on the eye and gives the patient an idea of comfort. Lens clearance may decrease as the scleral lens settles on the conjunctiva resulting in corneal bearing and patient discomfort. This settling time period will enable you to troubleshoot the diagnostic lens on the first visit, giving the first lens order a greater chance of success.
Perform over-refraction if the fit looks adequate after the lens has settled on the eye. A spherical over-refraction is usually sufficient, but in some cases a spherocylindrical over-refraction may be necessary if the patient is complaining of monocular diplopia or blurry vision. If astigmatism is found, Jupiter lenses can be ordered with cylinders from −0.25D to −15.00D (in 0.25D steps) with axes from 1 to 180 degrees (in one-degree steps).
Jupiter incorporates double slab-off ballasting to stabilize lens rotation. MSD lenses have not integrated astigmatic correction, so you must correct astigmatism with spectacles. Figure 2 shows a flow chart of the fitting process.
Figure 2. Fitting flow chart.
Fenestrations are 1mm holes located at the limbal clearance area in the scleral lens. Although necessary in previous designs to prevent suction to the globe and to allow more tear exchange, fenestrations are not necessary for newer designs, provided that the scleral lens is properly fit. Scleral lenses today are made of sufficiently high-Dk/t materials, often dismissing oxygen permeability as a reason for fenestrations. Even then, every scleral lens manufacturer has its preference whether to include them or not.
There are several advantages to fenestrations in scleral lenses. Fenestrations are physical holes in the lens, and therefore increase fluid and air exchange. This prevents suction of the lens to the globe and enhances lens removal. Furthermore, fenestrations allow for more oxygen permeability to the cornea, resulting in further prevention of corneal edema, dehydration, and neovascularization. As a result of increased tear exchange, fenestrations reduce the accumulation of metabolic waste products between the scleral lens and cornea with increased wear time.
Conversely, there are disadvantages to fenestrations as well. Fenestrations expose the tear layer to the outside air, which can result in both patient discomfort and blurry vision. Patient discomfort results from small air bubbles entering through the fenestration, which can lead to corneal compromise with increased wear time. The bubbles can also make the fitting process more difficult as well. Fenestrations also allow the passage of mucus and/or lipid from tears, which ultimately gather in the tear layer, resulting in blurry vision.
Many fitting sets including the MSD and Jupiter lenses contain fenestrations; however, you can order fitting sets without fenestrations. If small bubbles pose a problem while fitting fenestrated lenses, placing the fenestration at the 12 o'clock position upon lens application can simulate a non-fenestrated fit. The upper eyelid will usually cover the fenestration, preventing air from entering.
Comfort with or without fenestrations has not been shown to differ clinically, and fenestrations may still be considered for compromised corneas that are in need of increased oxygen or in the case of excessive tear debris collecting under the scleral contact lens.
Application, Removal, and Care
Proper application and removal techniques must be taught to ensure success with scleral lenses. For lens application, patients can place the lens on a DMV plunger or use a three-finger support technique. Prior to application, patients must fill the scleral lens with fluid. Preservative-free saline or preservative-free artificial tears are recommended to help avoid a delayed hypersensitivity reaction to any of the common preservatives used in saline and artificial tears. Saline can provide clearer vision compared to artificial tears due to viscosity, but artificial tears have been reported to offer increased initial comfort for the patient. Saline sprays, which can cause bubbles under the lenses, are not recommended.
After filling the scleral lens, have patients place a mirror on a flat surface and open their eyes wide while looking down into the mirror. With one hand holding the lens, have patients slowly bring the lens to the eye while the other hand is holding the lower lid until the scleral lens reaches the eye and stays in place. If a patient is intimidated by lens size, you may hold the upper lid on first application. Once application is completed, patients should carefully observe the eye to ensure there are no insertion bubbles between the scleral lens and cornea. If bubbles are present, the lens should be removed and reapplied.
The easiest method to remove the lens is to use a DMV device. It is vital to educate the patient to place the DMV near the bottom edge of the lens and lift away from the eye to break the suction, which will facilitate removal. If the DMV is placed in the middle, the equal surface tension between the scleral lens and conjunctiva will cause adherence, which will make removal difficult and uncomfortable.
Both soft lens and GP lens care systems may be recommended. However, the viscosity of GP lens conditioning solutions, if left on the lens, can cause blur upon application.
Follow-Up Care and Troubleshooting
It is essential to ensure that tear exchange is being maintained, especially with non-fenestrated lenses. To test this, with the lenses instilled, place a liberal amount of fluorescein in the patient's eyes and wait up to 10 minutes. Afterward, use the slit lamp to view the tear layer. If you see fluorescein in the tear layer, then tear exchange is occurring. This will aid in evaluating the amount of vault in the corneal and limbal zones. Observe the edges of the scleral zone to make sure there is no evidence of any lens impingement, blanching, or misdirection of conjunctival blood vessels.
Lens observation and a thorough case history will aid in troubleshooting the lens fit. Table 2 shows methods to troubleshoot the MSD and Jupiter lenses. If a patient complains of the lens hurting after several hours of wear, it is usually associated with corneal bearing. If you see central bearing, increase the sagittal depth of the MSD lens or steepen the base curve of the Jupiter lens. If you see bearing in the midperipheral or limbal area, increase the limbal zone clearance of the MSD lens or steepen peripheral curves 1 and 2 of the Jupiter lens. However, if you cannot avoid corneal bearing, you can piggyback the scleral lens with a high-Dk/t soft contact lens.
Bubbles under the lens can also cause a great amount of discomfort. Patients can avoid this with proper application techniques and making sure there are no bubbles under the lens immediately after application. If bubbles continue to be a concern, increase the lens diameter, going a step flatter in the MSD lens, or flatten the peripheral curve radii for a Jupiter lens.
If the patient reports discomfort as if the lens is pinching on the sides or if the patient has difficulty removing the lens, the scleral curves may be too tight. With scleral impingement, negative pressure builds behind the scleral lens, caused by the force of the blink. With each blink, the scleral lens flattens, allowing fluid to escape the tear layer, but with no equal fluid entering the tear layer, much like a plunger. Increasing the lens diameter, incorporating a peripheral fenestration, or flattening the periphery can often remedy this problem.
When a patient's complaint is blurry vision, lens flexure may be the cause. Keratometry or corneal topography done over the scleral lens while the lens is applied will reveal this, and increasing the scleral lens thickness can solve the problem. If you don't observe lens flexure, perform a sphero-cylindrical over-refraction to verify whether there is any residual astigmatism. Adding the cylindrical power on the scleral lens or having the patient wear spectacles over the scleral lenses can amend this.
Foggy vision is a common complaint for scleral lens patients. Metabolic waste and mucus trapped and accumulating under the scleral lens often causes foggy vision that gets worse with increased wear time. This is easily addressed by having the patient remove, clean, refill with saline, and reapply the lens every five hours or so. Fenestrations can be added to the lens to eliminate the need to remove and reapply the lens. A poorly wetting lens may cause foggy vision upon lens application and is easily remedied with a change in care system. Using an alcohol-based cleaner, adding a protein cleaner, or ordering the lens with plasma treatment will rectify this problem. Vision fluctuations are generally the result of excessive lens movement with each blink, which you can fix by increasing the sagittal depth or steepening the base curve.
The popularity of scleral lenses continues to grow due to the relative ease of fitting and the potential of giving patients who have irregular corneas a way to have clear vision without discomfort. With new designs made of high-Dk/t materials, scleral lenses have demonstrated safe physiological responses for the anterior eye.
Although working with larger-diameter GP contact lenses has the potential to be more time consuming, in a study of 32 keratoconic subjects being fit with scleral lenses (using trial lens fitting ), the first or second lens ordered was ultimately the lens that was prescribed 97 percent of the time (Schornack, 2010 ). This translates into an average of 2.8 visits needed and an average of 1.5 lenses ordered.
Scleral lenses, although not new, are becoming one of the leading ways to help patients who need a visual rehabilitative solution with contact lenses, especially in those who have advanced corneal thinning disorders. Although scleral lenses provide unique challenges in fitting, they have the potential to provide optimal and comfortable visual correction for patients. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #182.
|Dr. Li graduated from the SUNY State College of Optometry, after which he also completed a one-year Fellowship in Cornea and Contact Lenses. As part of this program Dr. Li gained expertise in fitting irregular and post-surgical corneas as well as refractive vision correction. Currently Dr. Li is associated with Manhattan Vision Associates where he is involved in both patient care and contact lens clinical trials.|
Contact Lens Spectrum, Issue: January 2011