GP lens eye Rounds

HIGH ASTIGMATISM: Front Toric Scleral Lens Fit

Andrea Lasby OD, FAAO, FSLS

History

• Chief Complaint: 45 year-old Caucasian male presented for a scleral lens fit OS to improve vision affected by post-LASIK ectasia.
• Ocular history:
  • LASIK OU 1997
  • Post-LASIK ectasia OS
  • Corneal Crosslinking OS 2022
• Systemic Health: Seasonal Allergic Conjunctivitis OU
• Medications: 1gt Pazeo QD OU.
• Family history: Father – Type II Diabetes Mellitus

Examination

• Entering visual acuities and manifest refraction:

Slit Lamp Examination

• Corneal Topography (Figure 1):

Figure 1: The corneal topography results were:

Sim K’s:  44.22/47.60@018
HVID  11.68mm

• • Pachymetry OS: Minimum corneal thickness 422um
  • Posterior Segment: unremarkable OU

Decision-Making Process

As this patient was looking for a comfortable lens for only his left eye; a scleral lens was recommended. He had no obvious scleral irregularities such as pingueculae or pterygia, so a scleral lens should be expected to perform well.

Fitting and Evaluation

• • Diagnostic fitting: Due to the peripheral elevation of the cornea, an oblate shape was chosen for the first diagnostic lens. The patient was originally fit with a scleral lens with edges that were 90um flatter the horizontal meridian and 90um steeper along the vertical meridian. Without scleral profilometry at the time of the fitting appointment, this strategy is typically successful for the majority of patients. However, for this patient the edges immediately had edge-lift/shadowing along the horizontal meridian and impingement along the vertical meridian, so the next lens attempted was a lens with spherical edges.

The second lens was a 9.00mm BCR/16.0mm OAD/-2.00D lens with 4650 sag and spherical standard edges. This showed excellent edge alignment 360˚ and good centration. There was a toric over-refraction with -1.00D cylinder. The initial vault was only 180um, but there was excessive limbal clearance (LC) of ~250um 360.

The following front toric lens was ordered in material (due to neovascularization noted on SLE): 9.00mm BCR/16.0mm OAD/-0.50 -1.00 x 034 Power, 4720 sag, -150 LC, std edges.

• • First dispense and 4-hour follow-up evaluation: Presenting VA OS with the scleral lens: 20/25-. The patient observed vision fluctuation with the blink, rotation: 5˚ CW, but rotated slightly off-axis under observation. Over-refraction: PL -0.75 x 084 20/20-. Settled 4-hour central vault: 232um. No blanching/impingement 360˚. Adequate limbal clearance 360˚. Plan: add base-down prism to help stabilize lens rotation, and use cross-cylinder to adjust for over-refraction.

The following lens was ordered: 9.00mm BCR/16.0mm OAD/-0.75 -1.00 x 054 Power  4720 sag,  -150 LC,  std edges,  2.0BD prism.

• • Final dispense and 4-hour follow-up: Presenting vision with the lens was 20/20-2 OS, and over-refraction did not improve vision further. Settled 4-hour central vault was 228um OS. There was no blanching/impingement 360˚, no excessive tear exchange, and limbal clearance was adequate (~50um) 360 degrees. The patient did not report any vision fluctuations, and no rotation of the lens was noted upon SLE.

At the one-month follow-up visit, the SL fit/comfort/vision was stable OS (Figure 2). It was recommended for him to return in six months for the next follow-up evaluation.

Figure 2: Final lens fit OS  

Clinical Pearls

• • Only approximately 6% of scleras are symmetric.¹ If any residual astigmatism exists for patients wearing symmetrical lenses, front toric designs are ideal to fully maximize BCVA.
  • There are many different ways to stabilize a front toric scleral lens such as prism ballast or dynamic stabilization zones (thick and thin areas). Depending on the manufacturer, you may be able to incorporate both into the lens design if rotational stability is a problem.
  • If unable to stabilize the lens, consider a larger diameter lens, as scleral asymmetry increases the further distance from the cornea.

Source

1. 1. DeNaeyer G, Sanders D, van der Worp E, et al. Qualitative assessment of scleral shape patterns using a new wide field ocular surface elevation topographer. J Contact Lens Res Sci. 2017;1(1).