GP lens eye Rounds

KERATOCONUS: Impression-Based Scleral Lens Fit Case

Andrea Lasby OD, FAAO, FSLS

History

• Chief Complaint: 61 year-old caucasian male referred by their optometrist over five hours away for impression-based sclerals due to previous failures fitting scleral lenses and piggyback GPs in the past due to a poorly fitting notch OD, and corneal bearing and discomfort OU. The patient presented with no scleral lenses (no wear for > 72 hours), anticipating impression molds to be taken that day.
• Ocular history:
  • Keratoconus OU
  • Full Penetrating Keratoplasty (PKP) in 2008 OD (Figure 1a)
  • Primary Open Angle Glaucoma OU: Clearpath shunt OD 2018 (not currently taking any topical hypotensive drops)(Figure 1b)
• Systemic Health: Type II Diabetes Mellitus, Hypertension, Hyperlipidemia
• Medications: 1gtt Pred Forte QD OD, 500mg Metformin tab QD PO, Atorvastatin 10mg tab QD PO, Metoprolol 50mg Tab QD PO, allopurinol 200mg tab QD PO, amlodipine 10mg QD PO
• Family history: None.

 Examination

• Entering visual acuities and manifest refraction:

• Slit Lamp Examination

Figure 1: a) OD PKP b) OD superior-temporal clearpath shunt c) OS temporal injected pinguecula located where a typical scleral lens edge would land

• • Corneal Topography (Figure 2):

Figure 2: Corneal topography showed the following:

Sim K’s: 44.20 @ 036; 48.66 @ 126 OD 43.28 @ 107; 45.72 @ 017 OS
HVID: 12.18mm OD 12.03mm OS

• • Tonometry: 13mmHg OD, 14mmHg OS
  • Posterior Segment: retina WNL OU, Optic Nerve OD: C:D 0.80H/V, (+)LC, (+)PPA 360; OS: C:D 0.50H/V, (+)LC, (+)PPA temp

 Decision-Making Process

• • There are now many scleral lens design options such as notches and microvaults for fitting over scleral irregularities, arguably none can be perfected as efficiently as impression-based lenses. Given this patient was from five hours away, impression lenses were the best option to reduce the amount of expected visits to finalize the lens design. With the history of failing with piggyback lenses via his previous optometrist, he was desperate to find a new scleral lens option that could be successful.
  • He was educated that with all shunts/blebs, many follow-up visits are necessary to monitor for any erosions. Follow-up visits with his local optometrist are recommended at the first sign of redness, pain, or discharge after lens finalization.

 Fitting and Evaluation

• • New impressions were taken at the first visit. Following impressions, a 7.10mm BCR, 16.0mm diameter, 4800 sag diagnostic scleral lens was used to determine the over-refraction necessary to maximize vision. At this visit, the BCVA was determined to be 20/60+1 OD and 20/40+2 OS. The molds were then shipped to the manufacturer with this information to design the first lenses. The lenses were requested to be made of a 200Dk material (Acuity 200) and with fenestrations sup-temp and sup-nasal OU to promote as much oxygen transmission as possible and decrease suction. The lenses were also requested to have Hydra-PEG coating as our climate is extremely dry.
  • First dispense and 4-hour follow-up visit: Presenting VAs with the lenses were 20/80- OD, 20/30+ OS. Settled 4-hour vaults were 261um OD, and 211um OS. Rotation was aligned with 6 o’clock OU. There was mild tear exchange superior-temporal OD and superior OU. No impingement/blanching was present. The edges showed good alignment over the shunt sup-temp OD, and over both the nasal and temporal pingueculae OS. There was also an over-refraction of -1.00 DS OD, and -0.50DS OS which improved BCVA to 20/60+ OD and 20/25- OS. Plan: OD – order exchange with adjustment to power, and steepen edge just clockwise of the bleb area to decrease tear exchange in that area. OS – steepen superior and inferior edges.
  • Final dispense and 4-hour follow-up visit: Presenting vision with the lenses was 20/50-1 OD and 20/25-1 OS. Over-refraction did not improve vision further. Settled six-hour vaults were: 259um OD, 202um OS. No impingement/blanching 360˚ OU. Trace tear exchange sup-temp OD, and superior OS, but no edge awareness and no complaints of fogging (Figures 3 and 4). No signs of clinically significant corneal edema on OCT pachymetry nor clinical signs on biomicroscopy (e.g. corneal haze, microcysts, etc.). IOP stable OU. Plan: finalized OU, patient recommended to have +2.00 OTC readers for near (prefers further working distance). Patient released to the referring optometrist to monitor for any signs of hypoxia, bleb erosion, and other scleral lens complications every three months. The recent report from his optometrist after one year of scleral lens wear states the patient continues to do well in the lens with no complications noted, and his glaucoma specialist states the signs of the patient’s glaucoma are normal.

Figure 3: Final lens tear exchange OD and OS, which the patient found to be acceptable.

Figure 4a: Final OD lens fit; Figure 4b: Final OS lens fit (nasal picture lost)

Clinical Pearls

• • Consider impression-based lenses for extreme scleral irregularities, as well as in cases where patients value minimizing the number of follow-up visits necessary to finalize the lens design.
  • When co-managing with referring optometrists in situations where patients cannot easily return to the specialty lens practice, good communication is essential to ensure the referring Optometrist is aware of what clinical signs and symptoms to monitor for that could indicate a serious complication.
  • Fenestrations are an excellent tool to reduce lens suction. Ensure the fenestrations are small, and placed peripherally enough such that air bubbles are not introduced under the lens.
  • Ensure any habitual lenses have been discontinued for at least 72 hours before eye molds are taken to ensure the molds will not reflect the previous ill-fitting lens impressions left on the conjunctiva.
  • When fitting any scleral lens on top of a corneal transplant, ensure corneal pachymetry baselines are taken before the onset of lens wear, and are monitored with every follow-up visit to ensure no clinically significant corneal edema is induced by lens wear.

Beneficial Resources

1. 1. https://pubmed.ncbi.nlm.nih.gov/24631015/
   2. https://pubmed.ncbi.nlm.nih.gov/17224675/