Contact Lens Fitting in a Patient with ICRS Implants

Intrastromal corneal ring segments added a twist to the case of this patient with keratoconus.

By Thomas P. Arnold, OD

A 42-year-old Hispanic man presented with a history of keratoconus, first diagnosed approximately 14 years earlier. In 2004, he underwent bilateral implantation of intrastromal corneal ring segments (ICRS; Intacs, Addition Technology) as a treatment for keratoconus. After the procedure, he required full-time spectacles to correct a significant refractive error consisting of residual astigmatism. His desire was to be fit with contact lenses to match his active lifestyle, which included sports, family life, and his duties as proprietor of his own business.

TO THE POINT

In a case in which multiple attempts failed to produce scleral lenses that provided adequate BCVA, an approach that started from scratch yielded positive results.

INITIAL EXAM

Topography revealed highly irregular astigmatic corneas (Figures 1 and 2). However, the patient’s best corrected visual acuity (BCVA) with refraction and spectacle lenses was reasonably good.

His current spectacle lenses were OD +0.75 -5.00 X 059 and OS -1.50 -1.25 X 178. Manifest refraction was OD +0.25 -3.75 X 068 = 20/25 BCVA; and OS -1.00 -2.00 X 180 = 20/25 BCVA.

Keratometry was OD 42.25/45.25@138 and OS 43.00/46.50@083. Horizontal visible iris diameter was OD 11.6 mm and OS 11.7 mm.

Figures 1 and 2. Corneal topography acquired via the Pentacam (Oculus) showed that the patient presented with highly irregular astigmatic corneas.

SCLERAL LENSES, CHAPTER 1

After a discussion of alternatives, it was decided to proceed with a scleral lens evaluation. Scleral lenses are commonly used in the correction of irregular corneas for a variety of conditions including keratoconus, pellucid marginal degeneration, ectasia after refractive surgery, and high myopia. The presence of ICRS is not a contraindication to scleral lens use, but it does require close observation. ICRS can also, as will be demonstrated in this case report, lead to unexpected results and modifications to the final prescription.

Trial lenses were fit with the following parameters:

OD: 7.80 base curve (BC)/15.6 mm overall diameter (OAD)/4500 sag/-2.00

OS: 8.00 BC/15.6 mm OAD/4400 sag/-1.50

Over-refraction yielded the following:

OD: +1.50 -1.50 X 078 = 20/20

OS: +1.75 -1.25 X 050 = 20/20

Central clearance as measured by optical coherence tomography (Cirrus, Carl Zeiss Meditec) was OD 277 µm and OS 200 µm (Figure 3).

On slit-lamp observation, both lenses centered well. More sagittal depth was needed in the left eye. The edge landing in the right eye was slightly tight, so modifications were made to the order to flatten it slightly.

The patient was enthusiastic about the sharp, crisp acuity achieved during the fitting. Both eyes achieved 20/20 vision without the distortions and aberrations he had experienced with spectacle lenses.

Figure 3. Central clearance during the initial scleral lens fitting as measured on optical coherence tomography (Cirrus, Carl Zeiss Meditac) was OD 277 μm and OS 200 μm.

Figure 4. The initial scleral lenses.

The initial lenses (Figure 4) had the following parameters:

OD: 7.80 BC/15.6 mm OAD/4500 sag/-0.50 -1.50 X 078/edge +100 µm flat

OS: 7.80 BC/15.6 mm OAD/4500 sag/-0.87 -1.25 X 050/edge standard

When the lenses were dispensed, both the patient and I were surprised at his poor visual acuity: 20/60 in each eye. The lenses fit very well except for moderate compression in the vertical meridians.

Over-refraction yielded the following:

OD: +1.50 -2.25 X 070 = 20/20

OS: +1.00 -2.25 X 055 = 20/20

SCLERAL LENSES, CHAPTER 2

Thinking that some unknown error was made in the initial calculations, we ordered another pair of lenses with the following parameters:

OD: 7.80 BC/15.6 mm OAD/4500 sag/plano -2.50 X 074/edge +25 µm/+100 µm

Figure 5. Despite acceptable fit and comfort, the second set of scleral lenses did not yield desired results.

OS: 7.80 BC/ 15.6 mm OAD/4500 sag/-0.50 -2.25 X 052/edge +25 µm/+100 µm

Unfortunately, this second pair was no better than the first. The fit and comfort were fine (Figure 5). BCVA was OD 20/60 and OS 20/40. As with the first set of lenses, over-refraction showed a potential visual acuity of OU 20/20.

SCLERAL LENSES, CHAPTER 3

At this point, I was scratching my head and thinking that this lens design was somehow flawed for this particular patient. Therefore, I decided to try a different product that I had used successfully a number of times before.

A trial fitting of this lens yielded 20/25 BCVA. So a third pair of lenses was then ordered with the following parameters:

OD: 7.60 BC/16.0 mm OAD/4600 sag/-1.75 -1.50 X 015/edge standard/+90 µm

OS: 7.60 BC/16.0 mm OAD/4600 sag/-2.75 -1.25 X 048/edge standard/+60 µm

By now, the reader can probably guess what happened at the dispense. Sure enough, as before, fit and comfort were fine, but the vision was unacceptable (OU 20/100).

WHAT WENT WRONG?

The clinician would be correct in thinking that the 20/20 BCVA achieved at the fittings should be able to be transferred to the final product. This may well be the case, but, if so, what was happening?

Perhaps the lenses were rotationally unstable? Toric haptics failed to minimize rotation. Larger lenses could have been tried; however, the patient’s horizontal visible iris diameter was average. Maybe flexure was to blame? Whatever the case, the practice manager in me was telling me, “Move on.”

Figure 6. The patient was reassessed after multiple failed attempts at satisfaction with scleral lenses. Elevation was mostly flat throughout the pupillary zone.

MAJOR REASSESSMENT, NEW APPROACH

This case was obviously calling for a major reassessment of the data. It became apparent to me that I was missing a key element. I did what many clinicians have done in the past: went back to the drawing board and looked at all the data without preconceptions of what should work (but obviously was not working).

The facts were as follows:

• The patient’s BCVA was at least OU 20/25. Not bad for a patient with this condition.
• Tangential topographic maps showed marked distortion throughout the pupillary zone.
• The corneal apex was only moderately decentered—well within the pupillary zone.
• Elevation maps (reference sphere radius OD 7.88 mm/ OS 7.84 mm; diameter 8.00 mm) were mostly flat throughout the pupillary zone (Figure 6).

In reconsidering these facts, it became obvious that spectacles—which had no influence on the cornea—allowed this patient to see well. It might be conjectured that the ICRS were doing their job in smoothing the surface of the cornea, and the optical properties of a rigid contact lens were not a necessity.

I decided to embark on a new approach. I ordered custom toric soft lenses (hioxifilcon D 54%) empirically, with the following specifications:

OD: 8.00 BC/14.7 mm OAD/+0.25 -3.75 X 065

OS: 7.90 BC/14.7 mm OAD/-0.50 -2.50 X 016

A week later, the new lenses arrived. The patient’s BCVA was OD 20/25, OS 20/25, and OU 20/20.

The lenses aligned perfectly on axis with minimal rotation with blink. The patient described them as very comfortable.

CONCLUSION

Sometimes simpler is really better.

This case demonstrates the need to be a keen observer of the facts presented and not to be misled by what was done in the past. Even with this patient’s complex condition and surgical history, his needs could be met quite readily with a custom soft lens. Now he can enjoy his active lifestyle with good vision and comfort.

The author would like to acknowledge Jason Jedlicka, OD, for his valuable comments and suggestions.

Thomas P. Arnold, OD, FSLS
• optometrist, Today’s Vision Sugar Land, Sugar Land, Texas; program co-chair, International Congress of Scleral Contacts; adjunct faculty, University of Houston College of Optometry, Houston
• financial disclosure: AccuLens, Bausch + Lomb Specialty Vision Products, Blanchard Lab, Boston Sight Scleral, EyePrint Prosthetics, Oculus USA
• 281-242-2020; drarnold@2020sugarland.com