Keratoconus, a request for soft torics, and a deferred cross-linking decision
A 23-year-old university student comes to a private optometry practice in Salmiya asking for 'invisible' lenses. She was diagnosed with keratoconus in both eyes two years ago and was offered corneal cross-linking, which she postponed twice because of examinations. She has never worn contact lenses and wears glasses only for lectures. Refraction is −3.25/−4.50×005 giving 6/12 OD and −2.50/−5.00×170 giving 6/12 OS. Simulated keratometry is 51.2 D at 095 / 45.8 D at 005 OD and 49.8/44.9 OS, with inferior steepening on topography and no apical scarring. Thinnest pachymetry is 452 µm OD and 468 µm OS. Slit lamp shows no Vogt striae and no prominent Fleischer ring. She says a friend wears monthly toric soft lenses and wants the same because they are cheaper than the rigid lenses she was quoted elsewhere. She studies in air-conditioned laboratories but travels by bus and plays outdoor sport twice a week.
1. Explain why the soft toric request is problematic here, using the topography and refraction numbers. What would you say to her?
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What the data show.
- Sim Ks 51.2/45.8 OD give about 3.5 D of corneal toricity, yet the refractive cylinder is −4.50 - the corneal and refractive cylinders do not match. That mismatch is the signature of irregular astigmatism.
- Best corrected acuity is only 6/12 in each eye with clear media and a healthy fundus.
- Thinnest pachymetry 452/468 µm with inferior steepening on topography means established keratoconus, not a borderline suspect.
Why a monthly soft toric is the wrong lens. A soft toric is designed to correct a regular spherocylinder. It drapes over an irregular cone, so higher-order aberration (coma, trefoil) and the corneal/refractive cylinder mismatch persist. Realistically she would achieve little better than 6/12–6/18, in a lens that on a steep, decentred cone tends to decentre and to produce 3-and-9 o'clock staining. She would then conclude that contact lenses do not work for her, and lose more time.
What I say to her. 'Soft lenses will probably give you vision no better than your glasses, because your cornea is not the shape they were built to correct. Rigid lenses replace the irregular surface with a smooth tear layer and usually do much better. There is a second issue you need to weigh: your corneas are thin and still changing. No contact lens, soft or rigid, stops keratoconus - cross-linking does. Choosing the cheapest option now may cost you acuity later.' Then I book topography to compare with the previous measurement so we are both looking at whether it is progressing.
2. Assume she proceeds with a rigid lens. Describe your lens selection and fitting plan, including the measurements you take, and what you would modify at the first follow-up.
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Selection. A rigid gas-permeable corneal lens in a high-Dk material (Dk ≥ 100). If the cone is central and the lens decentres or is uncomfortable, move to a corneoscleral or scleral design; hybrids are an intermediate option.
Measurements before ordering.
- Topography: sim Ks, K max, cone location and eccentricity, and comparison with previous maps for progression.
- HVID, corneal diameter, palpebral aperture and lid position (a tight upper lid needs a different edge and diameter).
- Refraction and the over-refraction she achieves; tear film quality; previous lens history.
- Confirm she has been out of any lens before the topography so the map is valid.
Fitting logic. Start from a trial set with a base curve flatter than the flattest K by roughly 0.3–0.5 D steps, diameter 9.2–9.8 mm. Aim for three-point touch (central cone bearing with mid-peripheral clearance) or gentle apical clearance, depending on the cone's shape and position. Target edge clearance 0.3–0.5 mm and a lag of 1–2 mm on blinking.
First follow-up (30–45 minutes after insertion). Fluorescein pattern, centration and lag, over-refraction to 6/9 or better, comfort score, and a full corneal check for staining or oedema.
Modify one variable at a time - base curve by 0.1–0.2 D, then diameter, then edge lift. Changing curve and diameter together means you cannot tell which change produced the result. Warn her about 3-and-9 staining, solution intolerance, and the value of a spare pair given her travel and sport.
3. What are your stop-and-refer criteria, and how do you document her decision to defer cross-linking?
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Stop and refer back to the corneal service if:
- Topographic progression - K max rising by 1.0 D or more, pachymetry falling, or a change in refraction or acuity between visits;
- Thinnest pachymetry approaching 400 µm, or new apical scarring, Vogt striae or a prominent Fleischer ring;
- Acute hydrops - sudden pain, watering, marked acuity drop and corneal oedema: same-day referral, no lens wear;
- Lens intolerance, or acuity plateauing below a functional level despite a good fit;
- Any suspicion of microbial keratitis.
Documenting the deferred cross-linking. 'Patient declined' on its own is not a record. The entry should contain: the date cross-linking was first offered and the progression data that supported it; what was explained - continued ectasia, scarring, hydrops, ultimately keratoplasty, and that contact lenses do not arrest the disease; her reasons for deferring; the agreed re-review interval with repeat topography in 3–6 months rather than waiting for symptoms. Have her sign the entry and give her a copy, and send the topography report to the corneal clinic so the referral sits in their records too. That way, if the cornea progresses while she is in a rigid lens, there is a documented trail and a named destination for the referral.