The Beginner's Guide to Fitting Scleral Contact Lenses

The three main benefits to scleral lenses versus traditional RGPs:

1) Increased comfort

• No bearing on the sensitive cornea, the weight of the lens rests on the sclera

2) Decreased corneal distortion

• No bearing on the cornea reduces mechanical stress on the tissue

3) Larger optic zone

• More forgiving if the lens de-centers

Here is my rookie approach to fitting scleral lenses:

1) Look at the K’s

I use the patient’s keratometry readings to determine my starting point. Each set will have a fitting guide which will recommend a lens to begin the process. Currently, I average the patient’s K’s and then go one lens flatter.

For example:

K’s = 46.75/43.50 @ 095

Avg K = 46.75 + 43.50 = 90.25/2 = 45.125 -> ~7.5 BC

One step flatter in the fitting set is 7.7 BC – this is where I would begin.

2) Determine the best central fit

Using the above lens and making sure to add preservative free saline and fluorescein to the bowl, insert the lens on the patient’s eye.

Raise the patient high in the chair, cover the patient’s lap with paper towels, have the patient bend over and position his or her face parallel with the floor, and give a fixation target.

TIP: I find it works best to have the patient firmly hold their upper lid while you hold their lower lid with one hand and the plunger/lens in the other.

Also, almost overflowing the bowl with preservative-free saline will help avoid bubbles upon insertion. If you do get a bubble on insertion, make sure to remove the lens and reinsert.

After the lens is in, using an optic section and white light, evaluate the central fit. We want the lens to vault the entire cornea for maximum comfort. Usually I shoot for about 300 microns of clearance initially, as the lens will settle about 100-150 microns throughout the day. You can use the cornea for comparison (average corneal thickness is around 550 microns) or if known, you can use the center thickness of the lens for comparison.

If the clearance is too little, move to a steeper lens, or if too much, move to a flatter lens until the appropriate clearance is obtained.

3) Evaluate the secondary and peripheral curves

When evaluating the secondary (mid-peripheral) curve, check to make sure the limbus is vaulted. When evaluating the peripheral curve, check for conjunctival drag or blood vessel impingement which would suggest a tight fit.

Furthermore, difficulty removing the lens may also indicate a tight fit.

You want adequate edge lift to avoid impingement and allow tear exchange without inducing lens awareness or discomfort caused by edge standoff.

4) Look at the refraction

The same patient with the above K readings had the following refraction:

-1.50 -6.00 x 098

From the above K’s we know that this patient has about 3.75D of corneal astigmatism. Since the refraction is showing 6.00D of astigmatism, we know that not all of the astigmatism is corneal. This knowledge is useful during the over-refraction.

5) Over-refract

If there is no residual astigmatism, spherical over-refract the lens to BCVA. If a decent amount of residual astigmatism is present, anticipate the need for a sphero-cylindrical over-refraction for BCVA.

6) Order the lens

Easy! Call up the lab and order the lens. Tell them which base curve gave the best fit, the over-refraction, and any modifications to size or peripheral curves. A relationship with your lab consultant is beneficial. Ask for their advice if anything is unusual about the particular patient or fit.

7) Follow-up

Schedule follow-ups for as late in the day as possible in order to evaluate the lens once it has completely settled on the eye. At follow-ups I ask the patient about any comfort or visual concerns, evaluate the fit, and over-refract to ensure the power is correct. Make adjustments to the fit/power as necessary.