So, you took the plunge into
scleral lenses and now have a new, incredible, patient population to serve. Congratulations; this is an incredible skill to be able to offer your patients.
Check out these advanced fitting techniques (and tips) so you can be the best scleral lens doctor in town.
Scleral lens fitting techniques
1) Toric and quadrant-specific peripheral curves
Most patients do not have a spherical sclera. Years ago, we could only use scleral lenses with spherical peripheral curves and make the edges uniformly “tighter or looser”. Because of this, patients had conjunctival redness, midday fogging, and edge awareness. This was difficult to get rid of because making changes to the edges overall, helped problems in one meridian, but induced problems in another.
Now we know from recent studies that most people have an irregular scleral shape. A study done by the
Scleral Shape Study Group found that of 140 eyes, 5.7% of sclera had a spherical shape, 26.8% were toric, and 66.7% were largely asymmetric.
1Scleral shape also has nothing to do with corneal shape. If a person has an irregular cornea, they will not necessarily have an irregular sclera. Corneal shape is not a predictor of the shape of the sclera.2,3
The best way to assess scleral shape is by performing
scleral topography. There are a number of instruments that can do this if you are willing to invest in them. They are really fabulous tools to have. If you are not interested in purchasing another piece of equipment or software, however, let me teach you how to assess the scleral shape using a diagnostic scleral lens.
How?
Follow these steps:
1) Insert the scleral lens into the patient’s eye and let it settle for at least 10 minutes while you complete the over-refraction.
I would highly recommend inserting a trial lens that has toric peripheral curves (two meridians that have different elevations). Many companies now have diagnostic fit sets that include toric peripheral curves. You can upgrade your fitting set to one of these as it will save you a lot of time and increase your accuracy in fitting.
2) Next, measure where the flat and steep meridians are by turning the beam of your slit lamp and aligning it with the (usually flat meridian) markings on the lens. This will tell you where the flat and steep meridians on the sclera are without having to use a scleral topographer. For example, if you align the flat hashmarks with the light beam at 20 degrees, the lens has rotated 20 degrees to the right. The sclera is flatter at the meridian of 20 degrees and steeper 90 degrees away.
a) Look at the conjunctiva under each of these meridians (superior, inferior, temporal, and nasally
b) Is there impingement of the blood vessels under the landing zone? The landing zone of this meridian is too tight and needs to be flattened.
c) Is there lift-off at the edge or does the patient have edge awareness?
Tip: if after the lens settles and the patient can very easily feel the edge of the lens under their lid (like a scratching sensation) the lens edge is likely too flat, even if it looks aligned. Steepen this meridian for increased comfort but let it settle first for a few days before making any changes.
3) Use a fluorescein strip to insert fluorescein over the scleral lenses. I usually have the patient look down and insert the fluorescein onto the superior conjunctiva above the lens. Next, look under the slit lamp immediately and note if there is fluorescein seeping under the lens at any of the edges. These areas of seepage indicate the lens edges there are too flat. You can gauge how much to steepen the edges by assessing how fast and easily the fluorescein seeps under the lens. The faster the seepage occurs the flatter the edge is, and you will want to steepen it by greater degree.
I now fit 90% of my patients in scleral lenses with toric peripheral curves because I not only see an improvement in the comfort and midday fogging, but I also have scleral topography that corroborates this data prior to fitting patients in lenses.
Quadrant specific peripheral curves are also an option for patients who have very irregular scleras or who may just need a change in one meridian only. They allow for different elevations of the edges in four different meridians. In my experience, most patients do not need quadrant specific peripheral curves but I would use them if I had a small pinguecula in one meridian that didn’t need a full notch or microvault.
2) Toric limbal zones
How many times have you noticed that a scleral lens fits well, but the nasal and temporal limbal clearances (or superior and inferior) are close to the back of the lens?
This happens because the horizontal visible iris diameter (HVID) and the vertical visible iris diameters (VVID) many times are different. Again, the eye is not usually spherical.
One study of 88 patients, 50% male and 50% female, used a scleral topographer to compare the HVID to the VVID. The study found that the average nasal-temporal HVID was found to be 0.26 mm greater than the average superior-inferior VVID.4
For this reason, with a scleral lens that has a spherical back surface design, some patients will either have a superior/inferior or nasal/temporal limbal area that is much closer to the lens than the opposite meridian.
By specifying unique limbal clearances, you can not only have a more uniform clearance above the cornea, but you can center the lens better on the eye.
Some conventional scleral lens designs have the ability to make the clearances vary in two meridians, 180 degrees from each other (like toric haptics) and some can do quadrant specific limbal clearances.
It is easiest to see this difference if you have corneoscleral topography which can take these separate measurements. However, if you do not, you can look at the diagnostic fit and take HVID and VVID measurements with a ruler or slit lamp beam to identify whether your patient would benefit from this technology.
Each manufacturer has different availability of what they can and cannot do with their lens. The best is to ask each company that you work with if they can specify different limbal clearances.
Patient Case:
Here is a case of a patient who I saw who had a well fit scleral lens for everything except the back of the lens kept touching the superior nasal limbus, even after I increased clearances, increased limbal clearance overall, and specified toric peripheral curves. With the increased clearances, the lens got slightly heavier and started to sink down, once again touching the superior nasal limbus.
The original lens had these specifications: OD: Zenlens RC / 4500 Sagittal Depth / 15.4 Diameter / 7.42 Base Curve / -9.25 - 0.50 x 132 / Peripheral Curves: Horizontal: Flat 3, Vertical: Flat 1 / Flex Control 0 / Boston XO2 / Clear
I looked at her scleral topography, changed the ring diameter on the machine from 15.4 (the diameter of her scleral lens) to 12.8 which is approximately where her lens will traverse over the limbus and begin to land.
She had a difference in sagittal depth from one meridian to the other to the tune of 71 microns.
Each diameter of scleral lens lands starting at a specific area. For this patient with a 15.4 mm diameter lens, the lens was going to start transitioning into a limbal zone at 12.8 mm. I found the sagittal depths of the scleral topography at 12.8mm for both horizontal and vertical diameters to be: 3139 microns and 3210 microns. For this particular patient, the meridians are oblique instead of with-the-rule or against-the-rule.
I ordered a lens with different clearances over the different meridians: 4300 sag over the flat meridian and 4500 over the steep meridian. Even though this patient has oblique meridians, this centered the lens better so her limbal clearances were even. With this specification we were also able to remove the toric peripheral curves because the lens fit and centered better with a uniform edge.
The final lens had these specifications: OD: Zenlens RC / Horizontal Sagittal Depth: 4300 / Vertical Sagittal Depth: 4500 / 7.42 Base Curve / -9.25 - 0.50 x 032 / 15.4 Diameter / FLT2 Peripheral Curve 360 / Flex Curve 0 / Boston XO2 / Clear
This lens worked incredibly to vault off of the superior nasal limbus. I, and the patient, were both very happy.
3) Microvaulting or notching
Using microvaults or notches can be helpful in cases where patients have a great fit, but compression on an elevated area of the conjunctiva. Typically these are used for pinguecula but can also be used for mounds of scar tissue or glaucoma filtering surgeries in rare cases where patients are unable to function without a scleral lens.
Microvaulting is where you create a small area on the periphery of a scleral lens that is elevated to move over a mass of tissue. You do this by measuring the height of the tissue mass (here is where an OCT can be helpful because you can measure in microns), the width of the mass, and the positioning of this mass on the lens (3:00, 6:00, etc).
To order this specification, you will take these measurements and make sure you note the positioning of where you want the microvault to be in relation to where the lens rotates (using toric peripheral curves are great in this way because you can specify rotation in degrees).
If you have the capability, you can also use scleral lens designs to incorporate a notch, which, instead of grooving around and over the mass, creates a cutout in the lens so that the lens stops before reaching the tissue. To do this you will take similar measurements of where the mass is positioned in relation to the lens edge and where the lens rotates to on the eye.
Summary
These are some of my most frequently used advanced scleral lens fitting techniques in practice and I am learning every day. Hopefully, this inspires you to take on a tough case and try some different design options on your next
challenging scleral lens patient.
References
- DeNaeyer G, Sanders D, van der Worp E, et al. Qualitative Assessment of Scleral Shape Patterns Using a New Wide Field Ocular Surface Elevation Topographer. Journal of Contact Lens Research and Science. 2017(1).
- Bandlitz S, Baumer J, Conrad U et al. Scleral topography analysed by optical coherence tomography. Cont Lens Anterior Eye. 2017 Aug;40(4):242-247.
- Abass A. Artefact-free topography based sclera-asymmetry. PLoS One. 2019; 14(7).
- Abass A. Three-dimensional non-parametric method for limbus detection. PLoS One. 2018; 13(11).
