Article

REFRACTIVE FOCUS

WHEN SIMPLE IS BEST

I’m thrilled to be joining the Contact Lens Spectrum columnist team and to be taking over for David Berntsen, OD, PhD, whose work I greatly admire. As we both are in the myopia field, I’m tempted to take Dr. Berntsen’s baton of several columns on this topic and keep running with it, especially because I’m known for talking endlessly about myopia management; but just to be different, I’d like to talk about astigmatism.

With our expanded scope of practice and the benefits of new technologies, it’s imperative that we not lose sight of our key expertise, namely refraction: the power to clearly, comfortably, and skillfully correct ametropia, both simple and complex. Two cases sprung to mind when I was considering this first column, interesting cases in which difficult refractions—one with high astigmatism and one with unstable astigmatism—were ultimately solved by a simpler correction option than that initially prescribed.

A Case of High Astigmatism

Tamara (not her real name) was a 41-year-old Caucasian female who desperately wanted to wear contact lenses. With one colleague, she had trialed standard corneal GPs and found them too uncomfortable. She then trialed mini-scleral lenses and found them too difficult to handle, plus she was unhappy about the protrusion of the lens on her eye.

With another colleague, she had gone through a fitting process with hybrid lenses. He reported to me that the rigid portion had flexed on her extremely toric corneae, rendering her vision unstable. Tamara reported no discomfort issues with the lenses—only problems with unstable vision—and she felt that this was the end of the line; while utterly motivated to wear contact lenses, she felt that this was her last chance.

Tamara’s refraction was OD +6.00 –7.50 x 102 (20/20+) and OS +5.00 –6.75 x 068 (20/15–). Figure 1 shows her corneal topography. With 5.00D of astigmatism in her right eye and 4.75D in her left eye, substantial internal astigmatism was evident. Presuming that rotational stability would be a significant issue, I elected to fit her with the only type of GP lens that she had not yet trialed—a 13.5mm large-diameter lens designed to vault over unusual corneal shapes while landing on a relatively regular limbus. With better comfort compared to a smaller corneal GP and easier handling compared to a mini-scleral, these lenses can provide the best of both worlds and can be ordered with a toric front surface to correct any residual astigmatism.

Figure 1. Tamara’s corneal topography (tangential curvature) showing OD 4.91D and OS 4.67D of regular astigmatism.

We achieved a good fit on the relatively regular limbus, vaulting over the astigmatic central corneae without too much clearance on the flat meridian. As expected, there was residual astigmatism of 2.75DC OD and 1.75DC OS, so we ordered front-surface-toric lenses.

Then the adventure began.

The first set of lenses had no markings for either the patient or me to check alignment, so they were sent back to the lab. On return, the right lens sat perfectly and had a –0.75DS over-refraction. The left lens was sitting slightly temporally, had a similar over-refraction, and was rotating 10º, so I increased the diameter to 14mm and reordered both lenses.

With the second set of lenses, the right lens, which had previously sat perfectly, was now rotating 25º. The left lens was now rotating 45º, after rotating only 10º previously. The third set of lenses were adjusted for this additional rotation, with increased prism ballast to improve stability; the right lens sat back at the correct 6 o’clock position this time, while the left lens assumed the same rotation but resulted in a baffling over-refraction. The fourth set of lenses worked beautifully for the right eye, but the left was still showing a perplexing mismatch between rotation and refraction.

While this pair was suitable to take home and commence wear, and Tamara was still enthusiastic after four sets of lenses (!), I was becoming dubious of the feasibility of this lens design. In addition, I didn’t have any other rigid lens options open to me due to Tamara’s previous experiences. Hence, I formulated a simpler backup plan and ordered a trial pair of extended range monthly toric lenses.

The complex lenses lost the race—vision was too variable—while the simpler lenses won the day. Tamara’s soft monthly toric lenses had parameters of OD +6.00 –5.75 x 105 (20/30+) and OS +4.50 –5.75 x 070 (20/20), with a residual refraction of OD –0.25 –2.25 x 120 (20/20) and OS 0.00 –0.75 x 075 (20/20+). It would not be the first choice to end up with this much residual astigmatism, but given Tamara’s previous history with several rigid lens types, we have surprisingly achieved the most satisfactory solution to correct her vision with the simplest lens type. Tamara is extremely happy with her comfortable, stable soft lens vision. She wears “top up” glasses for computer work and driving.

A Case of Unstable Astigmatism

Robyn (name also changed), a 52-year-old Caucasian woman, presented as a new patient on referral from her ophthalmologist for rigid contact lens fitting. She had been diagnosed with Salzmann’s nodular degeneration (SND) almost 12 months earlier.

She had been managed conservatively over this time, and Robyn had no discomfort symptoms aside from unstable vision in glasses. She was becoming anxious about her vision deteriorating to the level at which she would be unable to drive and to work effectively as a night shift midwife. She was also a keen runner and was concerned about her visual confidence when treading the pavement in the hours before sunrise.

Figure 2 shows Robyn’s corneal topography. I had mini-scleral contact lenses on my mind, but first I had to give her refraction its best shot. I measured her acuity with her current glasses, which had a prescription of OD –1.00 –1.75 x 100 (20/25–) and OS –3.00 –0.75 x 120 (20/25, but reporting blur from 20/40), noting that she thrust her chin up to see with her right eye, then read haltingly with her left eye. My refraction at this visit was OD +0.75 –3.00 x 092 (20/25+) and OS +1.50 –3.50 x 100 (20/20). Needless to say, there was quite a bit of difference between Robyn’s glasses and my first refraction. I told Robyn to forget the SND for a moment, as that much over-minus would make anyone’s vision feel unstable.

Figure 2. Robyn’s corneal topography (tangential curvature) showing OD 6.51D and OS 7.00D of irregular astigmatism due to Salzmann’s nodular degeneration.

With such good acuity, we elected to correct her with spectacles first and to assess stability of her refraction over time. Five months later, her vision had deteriorated to OD 20/30– and OS 20/25+ with these new glasses, but improved again with a second refraction of OD +1.00 –3.00 x 070 (20/25) and OS +2.00 –4.50 x 101 (20/20), so her lenses were changed. Another five months afterward, her refraction had changed again, but this time with minimal change to her acuity: OD +0.75 –3.25 x 070 (20/30+) and OS +2.50 –5.50 x 101 (20/20–).

Robyn may yet need mini-scleral contact lenses; as SND slowly progresses (Maharana et al, 2016), her prescription may become too much of a moving target to continue with spectacle correction. For the moment, though, she understands that we are on a refractive adventure together and that further options are available to her as her vision changes.

Remember the Fundamentals

For both Tamara and Robyn, more complex contact lenses could provide the solution to their ametropia but were not the best choice for their individual reasons. We are fortunate to have so many outstanding tools for correcting refractive error. With expanded scope of practice, the latest technology, and improved knowledge, we can solve more refractive puzzles than ever before as well as manage all aspects of healthy contact lens wear. However, these two patients made me reflect on the fundamentals—a careful refraction and a simple correction are often the best. CLS

For references, please visit www.clspectrum.com/references and click on document #270.