High myopia with astigmatism: vertex correction, toric rotation, and an orthokeratology request

Vertex correction is applied to each principal meridian separately; it changes power but never the axis.

• 180° meridian: −9.00 D spectacle. F(cl) = −9.00 / (1 − 0.013 × (−9.00)) = −9.00 / 1.117 = −8.06 → −8.00 D
• 90° meridian: −9.00 + (−2.50) = −11.50 D. F(cl) = −11.50 / (1 − 0.013 × (−11.50)) = −11.50 / 1.1495 = −10.00 → −10.00 D
• Resulting cylinder: −10.00 − (−8.06) = −1.94 → −2.00 D at 180

So the order is approximately −8.00 −2.00 ×180.

The cylinder shrinks because vertex compensation is non-linear: the more minus the meridian, the larger the denominator, so the two meridians converge toward each other. Cross-check with the spherical equivalent: −10.25 D at 13 mm becomes −9.05 D, and the −2.00 D cylinder is consistent with that scaling. The friend's −8.00 D sphere leaves roughly 2.25 D of uncorrected ametropia, which explains the general blur; the 'smearing' of lights is the uncorrected 2.50 D of astigmatism. Both findings are expected, not evidence of a bad refraction.

These are two linked findings pointing to one problem: rotational instability, not a power error.

A cylinder of 2.00 D misaligned by θ leaves residual cylinder of approximately 2 × F × sin θ = 2 × 2.00 × sin 20° = 1.37 D, at an oblique axis. That matches the −1.25 ×090 found on over-refraction. The small +0.75 sphere is largely artefactual (a rotated cylinder generates a spherical equivalent shift), so increasing the cylinder power would be the wrong response.

Next steps, in order:

1. Confirm reproducibility. Reassess rotation on at least two separate visits and after 20–30 minutes of wear; a lens that rotates during insertion often settles. Document with the slit beam and the laser marks.
2. If a consistent 20° clockwise rotation is confirmed, compensate by ordering the axis rotated against the direction of rotation (here, 20° counter-clockwise from the target axis), then verify on the eye before dispensing a supply.
3. Improve rotational stability if compensation is unreliable: larger diameter (about 14.5 mm), steeper base curve, thinner edge profile, or a prism-ballasted toric design.
4. Consider abandoning soft torics. With 2.25 D of corneal toricity, a rigid gas-permeable lens corrects the cylinder optically and removes the rotation variable entirely; counsel him about the 8-second tear break-up time and adaptation.

Also verify that the 11.8 mm HVID and 9 mm fissure can support a 14.5 mm lens decently on the eye.

He is outside the usual candidacy envelope. Modern orthokeratology lenses are typically validated and approved for myopia up to about −6.00 D with astigmatism up to roughly 1.50–1.75 D (toric designs extend somewhat further). At −9.00 −2.50 with 2.25 D of corneal toricity he would be an off-label, high-risk fit: the treatment zone would be small relative to the correction required, decentration and induced higher-order aberrations are common, and the endpoint of 'no lens during cycling' would likely not be achieved.

The relevant risks to discuss are microbial keratitis (the dominant concern with any overnight wear), corneal staining and epithelial thinning, and fluctuating vision across the day. A tear break-up time of 8 seconds is borderline for overnight wear and would worsen with lens-induced epithelial change.

Alternatives to offer:

• Daily disposable silicone hydrogel toric - the safest modality for his 5-day-a-week, 12-hour pattern, and appropriate for sport.
• Rigid gas-permeable lenses - better optics for high astigmatism and no rotation issue, though with a longer adaptation and a real risk of dislodgement during cycling; spectacles or goggles for cycling are sensible.
• Spectacles for swimming, with goggles; warn explicitly that swimming in any contact lens, especially in fresh water, increases Acanthamoeba risk, and that showering or swimming in lenses should be avoided.

Finally, he should stop borrowing another person's lenses; the current blur is optical, but the practice carries a real infection risk.