Patient snapshot
Patient: 74-year-old woman, lifelong short-sightedness, cataract developing in the right eye (her dominant eye)
Previous surgeries: LASIK to right eye, Cataract surgery (left eye) with a standard monofocal lens
Background
Years earlier, the patient had LASIK laser surgery on her right eye to achieve monovision – a setup where one eye is optimised for distance and the other for near vision. Later, she had cataract surgery on her left eye in London, where a standard monofocal lens was implanted. The intention had been to leave her short-sighted with good unaided reading vision, but the surgeon forgot this during surgery and inserted a lens power aimed at giving clear distance vision. He acknowledged this post-operatively and the patient accepted that these things can happen. She continued with good distance vision in each eye and started using glasses for reading.
Some time later a cataract developed in her right eye, the one that had previously received LASIK. Her clear wish was to regain the ability to read without glasses following cataract surgery.
Why this case was particularly tricky – three challenges:
LASIK makes measurements less reliable. When the cornea has been reshaped by laser surgery, the standard calculations surgeons use to choose the correct lens power become less accurate. The final result could end up more long-sighted or more short-sighted than planned, thus requiring glasses for clear vision. This is the outcome that such patients mostly want to avoid, having previously paid for surgery to avoid the need for glasses.
Her dominant eye had to stay in balance. Her left eye (already treated) had been left with clear, unaided distance vision. If her right eye – her dominant eye – were made too short-sighted, the brain would start to rely on the “wrong” eye for distance, causing confusion and discomfort. This is known as “flipping the dominant eye” and can lead to uncomfortable binocular vision.
A standard multifocal lens was ruled out. The shape of her cornea following LASIK, combined with the risk of halos and glare at night and a flat corneal profile, made a multifocal implant unsuitable for her.
Therefore, the right eye had to remain her dominant eye by retaining good distance vision, while also giving good enough near vision to enable reading without glasses, and all without using a multifocal lens implant.
The surgical decision and treatment plan
The initial question was whether an extended depth of focus (EDOF) lens could provide adequate reading vision.
An EDOF lens – short for “extended depth of focus” (also known as an “increased range of focus” lens) – does not just correct for one distance. It stretches the range of clear vision, giving patients a deeper zone of in-focus vision from arm’s length to distance, without the visual trade-offs of a full multifocal design.
Key clinical insight
| When a patient has had LASIK and subsequently needs cataract surgery, standard measurements with standard mathematical calculations and a standard lens approach often will not deliver the result they are hoping for. Choosing an EDOF lens with a carefully considered refractive target – one that accounts for measurement uncertainty and the patient’s priorities – can unlock excellent outcomes that a simpler approach would have missed. |
The chosen plan: an EDOF lens targeting -1.00 Dioptre instead of 0.00 or -0.50 D
The rationale for choosing the more myopic target:
- Accounting for LASIK uncertainty. Since measurements after LASIK are less precise, targeting slightly more short-sightedness provides a safety buffer. If the result lands more long-sighted than planned, the patient still ends up in a clinically useful range with good vision.
- Reading really matters to her. For patients where unaided near vision is the top priority, a target of −1.00 D with an EDOF lens is more likely to deliver comfortable reading than −0.50 D. The extra step toward short-sightedness provides more power in the reading zone.
- Keeping both eyes working together. With -1.00 D in the right eye and the left eye already set for clear distance, the two eyes complement rather than compete, giving the patient a full and comfortable range of unaided vision between them.
- With the right eye targeting -1.00 D the distance vision is still very good and allows the right eye to remain dominant. Therefore, we avoid “flipping the dominant eye”.
How it turned out
The patient achieved exactly −1.00 D, landing precisely on target. The outcome exceeded expectations across all key measures:
- Excellent unaided reading vision
- Good unaided distance vision in the right eye and excellent unaided distance vision with both eyes open and working together.
- Full range of binocular vision (both eyes working together)
- No dominance problems – no confusion between the two eyes
- No anisometropic symptoms – no discomfort from the difference between the two eyes
- Completely glasses-free for everyday tasks
