Who Is a Candidate for PRESBYOND?

What decides suitability

A blended vision plan asks the cornea to do something specific: hold two different corrections across two eyes, with enough tissue left for the eye to remain stable. The assessment is essentially checking whether your eyes can support that, and whether the result would be worth having.

Three kinds of question are being answered at once. Can the cornea spare the tissue? Will the surface heal predictably? And is a difference between the eyes likely to be tolerable for this person, given their work, their hobbies and their expectations?

Only the first two are measurements. The third is a conversation, and it is the one patients sometimes skip because the scans look reassuring.

Prescription and stability

PRESBYOND is used for people who are short-sighted or long-sighted and who have started to lose near focus. The refractive error is treated at the same time as the presbyopia is compensated for, which is why the assessment begins with a careful refraction rather than with the reading vision question alone.

Stability is the part that cannot be rushed. A prescription that is still changing, particularly in a younger person with progressing short sightedness, means the treatment is aimed at a target that will move. Previous records help: bringing an old prescription to the consultation is more useful than describing it from memory.

Astigmatism is not a barrier in itself. It changes the ablation profile and the amount of tissue required, which is a planning question rather than a yes or no.

Corneal shape and thickness

Every laser correction removes tissue, and the amount needed rises with the size of the prescription. Thickness and shape therefore set a limit on what can be done safely, and the assessment measures both.

Topography is looking for an irregular or unstable surface, including keratoconus and the suspicious shapes that precede it. Those findings are the main reason a cornea is declared unsuitable, because removing tissue from a cornea that is already structurally compromised is the mechanism behind the rarest and most serious complication of refractive surgery.

This site does not publish a minimum thickness figure. Thresholds differ between surgeons and platforms, the measurement depends on where and how it is taken, and a number here would be read as permission.

The ocular surface

Dry eye is common, often unnoticed, and directly relevant. A compromised tear film makes the measurements less reliable, makes healing less comfortable, and makes a patient more likely to be unhappy with the result even when the surgery went exactly as planned.

The usual approach is to identify it first and treat it before surgery, which can mean weeks of lubricants, lid hygiene or other management. If a clinic is willing to operate on an obviously dry eye without addressing it, that is a reason to ask why rather than a reason to feel reassured about the speed of the process.

The dry eye article covers the mechanism and the management in more detail; it is written about SMILE Pro, and the ocular surface principles are the same.

The lens and cataract

Presbyopia is a lens problem, so the lens is examined rather than assumed. An early lens opacity that is not yet affecting vision may not change the plan. A cataract that is already reducing vision usually does, because replacing the lens addresses both the cataract and the near vision in one operation, and a corneal laser procedure would leave the cataract to be dealt with later.

This is one of the reasons age is not a rule. Two people of the same age can have very different lenses, and the examination rather than the birthday decides which category of treatment is sensible.

After previous surgery

Previous LASIK, SMILE or PRK is not automatically disqualifying, but it changes the calculation in three ways: there is less tissue available, the surface may be less regular, and the original treatment has to be understood before a second one is designed.

Ask what records the clinic needs and bring them. Treatment zone, ablation depth and the original refraction are the details that make a second plan possible rather than speculative. A clinic willing to plan without them is guessing about the constraint that matters most.

Dominance and binocular vision

A blended plan assumes the two eyes can be given different jobs and that the brain will cooperate. Eye dominance is measured, and any existing binocular problem is relevant: a person who already suppresses one eye, or who has a longstanding strabismus, needs that discussed explicitly rather than discovered afterwards.

This is also where the honest limits of measurement sit. There is no scan that predicts adaptation. A contact lens trial, where a clinic offers one, is the closest thing to a test of tolerance available before the surgery.

What the assessment measures

When the answer is not now

A good assessment produces a plan, and sometimes the plan is to wait or to choose something else. The situations below are the common ones.

• The prescription is still changing. Waiting for stability is not delay for its own sake; it is what makes the result hold.
• The ocular surface is unstable. Treating it first usually improves both the measurements and the experience.
• A cataract is developing. Lens surgery may address more of the problem in one operation.
• The cornea cannot spare the tissue. A different procedure, or none, is the honest answer.
• The trade-offs are not acceptable to you. That is a legitimate reason, and it does not need a clinical justification.

Questions to ask your ophthalmologist before PRESBYOND

1. What target refraction would you plan for each eye, and what is it about my eyes that sets it?
2. How much corneal tissue would this leave, and what is your margin for a refinement later?
3. What did my tear film and lid margins show, and does anything need treating first?
4. Is my lens clear enough for a corneal procedure, or would lens surgery be more sensible?
5. What is your plan if I do not adapt to the difference between the eyes?
6. Can I trial the concept with contact lenses before deciding?
7. What would make you advise against this treatment for me?