GP lens eye Rounds

KERATOCONUS: Higher Order Aberration Scleral Lens Fit Case

Andrea Lasby OD, FAAO, FSLS

History

• Chief Complaint: 35 year-old caucasian male with a history of scleral lens wear for the last six years to improve irregular astigmatism due to keratoconus OU. Overall, he was happy with the lens comfort, but returned hoping for new options to improve his best corrected vision further.
• Ocular history:
  • corneal crosslinking in 2010 OU.
  • previously tried off-label brimonidine at night to help with glare, but wasn’t subjectively effective so discontinued
• Systemic Health: WNL
• Medications: none
• Family history: Keratoconus – father and brother

Examination

• Entering visual acuities and over-refraction with presenting scleral lenses:

• Slit lamp examination

• Corneal Topography (Figure 1):

The corneal topography findings were:
Sim K’s: 47.55/52.03@156 OD 47.68/49.97@018 OS
HVID: 11.77mm OD 11.8mm OS

• • • Minimum Corneal Thickness: 455um OD, 423um OS
    • Posterior Segment: unremarkable OU
    • Higher Order Aberration (HOA) Screening over current scleral lenses (Figure 2):

Figure 2: HOA Zernike Plots show significant aberrations OD>OS, most markedly high vertical and horizontal coma OU. RMS values are 1.12um OD, 0.71um OS.

Decision-Making Process

• • Screening aberrometry over top of the current scleral lenses shows this patient exhibits high amounts of higher order aberrations OU. With the root mean square (RMS) of his lenses > 0.70um OU, he is a good candidate for achieving a significant subjective improvement in his vision with HOA correction.
  • The patient was excited to try new technology, and was cautioned on his prognosis. Further surgical intervention (corneal transplants) was not considered as the patient was not at risk for hydrops/perforation, and visual performance and comfort with scleral lenses was satisfactory.
  • He was educated that some aberrations may still be present after correction, but the goal was to have them less apparent.
  • His current scleral lens manufacturer did not offer HOA correction at this time, so he decided to proceed with impression-based lenses with the intention of decreasing the number of remakes necessary for a proper fit over top of his nasal pingueculae.

Fitting and Evaluation

• • Patient returned six weeks later for impressions of his cornea and sclera after not wearing his current scleral lenses for over 72 hours. At this time, the laboratory was informed of our goal to proceed with HOA lenses, so the first lenses were sent with alignment dots already on them to decrease the number of remakes. Lenses were ordered with base curve and power measurements from his previous lens design.
  • First dispense and 4-hour follow-up visit: The settled (after two hours) central vaults were 227um OD, 297um OS. Rotation was aligned at 6 o’clock OU. No impingement/blanching 360˚ of the landing zone was observed OU, and adequate limbal clearance 360˚ was evident OU. OR: +0.25DS 20/30 OD; PL OS 20/20-2. New aberrometry data was sent to the manufacturer. Plan: order new lenses, with HOA correction and over-refraction OD. No fit changes were necessary OU.
  • 2nd dispense and 4-hour follow-up visit: Stable fit OU, no changes from previous visit. Presenting VA with sclerals: 20/30+1 OD; 20/20 OS. OR: -0.25 – 0.50 x 085 OD 20/20-2; PL NI OS. Aberrometry RMS improved to 0.25um OD and 0.31um OS. Plan: OD: Order new HOA lens with OR adjustment OD, OS: finalized.
  • Final dispense and 4-hour follow-up visit: Stable fit OU, no changes from previous visits. Presenting VA with sclerals: 20/20 OD, 20/20 OS. OR: +0.25 – 0.25 x 115 OD NI. Fit tentatively finalized OU. Final aberrometry RMS improved to 0.32um OD.(Figure 3)

Figure 3: Final aberrometry Zernike plots: very few types of aberration considered clinically significant OU; both vertical and horizontal coma minimized OU. OD still shows some oblique secondary astigmatism, and OS shows some spherical aberration, but much improved overall.

• Final 3-week follow-up: Stable fit OU, stable BCVA OU. No significant O/R OU. Patient very satisfied with comfort that lasts at least 14 hours, and vision is much improved, especially at night. Plan: fit finalized OU. The final aberration comparison is shown in Figure 4.

Figure 4. Final aberrometry comparison. OD shows RMS improved from 0.90um at first dispense, to 0.32um in final lens. OS shows RMS improved from 1.02um at first dispense to 0.25um in final lens.

Clinical Pearls

• • Consider utilizing aberrometry to correct for HOA’s with BCVA better than 20/30 in current sclerals (or diagnostic sclerals if starting with a neophyte wearer).
  • Check with your manufacturers if they currently offer this technology. Consider adding a laboratory to your inventory if you don’t have a relationship with a company who offers HOA options.
  • Ensure your patient has dark-adapted for at least 15 minutes before taking aberrometry scans to ensure pupils are as large as possible. For patients with pupil sizes less than 6.0mm, consider dilating the patient for these scans: reinsert lenses and let them settle 30 – 60 minutes.
  • HOA lenses are not for everyone. Consider the following when recommending HOA lenses for patients:
    • RMS > 0.30-0.40 (to ensure clinically significant improvement in vision possible)
    • No corneal scarring
    • No cataract (any opacity along the visual axis)

Beneficial Resources

1. 1. https://journals.lww.com/optvissci/abstract/2014/10000/wavefront_guided_scleral_lens_correction_in.14.aspx
   2. https://iovs.arvojournals.org/article.aspx?articleid=2782001
   3. http://clspectrum.com/issues/2021/august/wavefront-corrected-sclerals-from-theory-to-reality/