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CASE REPORT: Pinguecula notch in a scleral lens

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By Celia Bloxsom
BAppSci(Optom)Hons GradCertOcTherap

 

In the contact lens world scleral lenses are the ‘new black’. Why not? They have so many advantages over corneal RGP lens designs: better comfort than corneal lenses, no fear of loss, help heal diseased ocular surfaces and even aid in averting surgery in some cases.

Our intense UV levels in Queensland make our state a leader in pinguecula, which cause a great amount of trouble when fitting scleral lenses. This case shows how introducing nasal ‘notches’ to scleral lenses resolved some issues with comfort and hyperaemia, and created eventual lens wear success.

My patient, NH, was referred for contact lens fitting. NH had bilateral pellucid marginal degeneration (PMD) and although achieving good visual acuity with glasses, she experienced poor low contrast and wanted to try contact lenses. Her spectacle prescription and visual acuity is:

R +1.00 / -4.75 × 97  (6/7.5++)   L +3.25 / -6.25 × 93  (6/9++)

Fitting corneal lenses for PMD is challenging, as PMD ectasia typically affects the inferior peripheral cornea more so than keratoconic ectasia, which therefore creates a lot more inferior lens decentration (Figure 1). Scleral lenses were a great option for NH to aid centration.

CL OL 13 Celia Bloxsom Figure 1 Topography - F

Figure 1. Topography image

I conducted a trial fitting with the KATT lens design (Capricornia). KATT lenses are best fitted by determining the corneo-scleral sagittal height (sag) along a 15 mm chord and then choosing a trial lens based on this measurement.

Although the Smith Technique is often described as a way to use the biomicroscope to measure corneo-scleral sag, I find a much easier way is to determine the corneal sag across a 10 mm chord via topography, found in the analysis details section of a Medmont topographer, and adding 2,000 microns to it to determine the sag for a 15 mm chord.

This technique of determining corneo-scleral sag gives a fairly accurate measurement of corneo-scleral sag that you can then confirm with the aid of the diagnostic lens set.

In the standard KATT trial set, all 12 lenses are listed in order of sag height. A trial lens should be selected from the set that has a sag height higher than the predicted corneo-scleral sag plus a clearance factor of between 200-400 microns.

I calculate 400 microns onto the corneo-scleral sag, as I know that the lenses settle back towards the cornea considerably after insertion, continue to do so for six to eight hours after insertion, and in some cases can lose up to 200 microns of clearance.

Once trial lenses were selected and inserted, they were allowed to settle for 30 minutes and anterior OCT images were taken to assess the corneal clearance (Figure 2). From the trial fitting, the following front surface toric KATT lenses were ordered:

R 6.80 / 16.50 / KATT Lens  Design / 50/45S / -6.75 / -1.00 × 140

L 6.80 / 16.50 / KATT Lens Design / 50/45S / -6.50 / -4.25 × 167

CL OL 13 Celia Bloxsom Figure 2 OCT Image Of RE Lens Clearance - F

Figure 2. OCT image

Initially, all went well with comfort and vision after the custom lenses were delivered but NH reported considerable conjunctival hyperaemia and irritation after the lenses were removed, which did not settle for up to an hour.

When scleral lenses are removed, I expect 5-10 minutes of rebound hyperaemia but it should settle quickly and not cause irritation, so NH’s reaction was unusual. I asked NH to wear the lenses into the practice after all-day wear, where I removed them and inspected the corneal and conjunctival surface.

Although the lenses did not touch any part of the cornea (confirmed with OCT) and settled in alignment on the sclera peripherally, it caused significant compression of the raised pingueculae present nasally on both eyes (Figure 3).

CL OL 13 Celia Bloxsom Figure 3 Inflamed Pinguecula After Scleral Lens Removal - F

Figure 3. An inflamed pinguecula after scleral lens removal (not patient NH)

Any alteration of the lens periphery, through either the T1 or T2 curves, would both impact on central clearance (with alterations to T1) and limbal clearance (with alterations to T2), as well as losing the peripheral alignment that worked well in the superior, temporal and inferior quadrants.

After discussing the situation with Jodie Davenport, lens designer and technical advisor for Capricornia Contact Lens Laboratory, I was able to mark on the lens, using a felt-tip pen, where the location of the pinguecula was beneath each lens periphery.

This was important, as the lenses were front surface toric lenses and rather than being able to notch a spherical lens anywhere in the periphery, the location of this notch had to be very specific to keep the inferior marker in place at 6 o’clock and ensure the vision remained clear. The results of this notch are shown in Figures 4 and 5.

CL OL 13 Celia Bloxsom Figure 4 Right Lens Nasal Notch - F

Figure 4. Nasal notch on right lens

CL OL 13 Celia Bloxsom Figure 5 Left Lens Nasal Notch - F
Figure 5. Nasal notch on left lens

With front surface toric scleral lenses, the marker must be inserted by the patient at 6 o’clock in the on-eye position to ensure good vision, as the KATT lens has no prism ballast to rotate the lens to that position.

Usually, once the KATT lens is inserted, it does not rotate through the day. This is very patient dependent, with some of my patients’ lenses slowly twisting throughout the day and requiring prism ballast for stability. The extra bonus of this nasal notch, used to alleviate pinguecula compression, also aids to further stabilise the lens on the eye.

To be able to fit scleral lenses, trial kits are essential but settling of scleral lenses takes considerable time, recently reported to be up to six to eight hours* and many issues, like compression on a pinguecula, cannot be diagnosed through trial lens fitting alone.

If issues like this do occur, good communication with your laboratory can help create individual options to fix these issues.

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* Let’s settle this once and for all: a comparison of scleral lens settling. Adeline Bauer, Josh T Lotoczky. Michigan College of Optometry, Vision Research Institute.



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