Am I a Candidate for LASIK? A Sydney Refractive Surgeon’s Suitability Checklist

Most healthy adults with a stable prescription in the treatable range are candidates for some form of laser vision correction. Whether LASIK specifically is the right one comes down to two things no online quiz can tell you: how thick your corneas are, and what shape they are. That is settled by measurement.

Worth saying up front: being unsuitable for LASIK does not mean being unsuitable for vision correction. Thin corneas. An uneven corneal surface. A prescription the laser cannot reach. Reading vision that has already started to slip. Each of those points you somewhere else: PRK, ICL surgery, PRESBYOND, or refractive lens exchange.

Below are the criteria a refractive surgeon actually checks, and what happens when one says no. If you already know you want LASIK at Pure Sight, this is the step before it.

The short answer: six things that decide whether you can have LASIK

1. Age and stability. Adults from around 21, with a prescription that has held steady.
2. Prescription in range. Your degree of short- or long-sightedness sits inside what the laser can safely treat.
3. Corneal thickness. Enough tissue to reshape and still leave a safe amount behind.
4. Corneal shape. Regular in shape, with no signs of keratoconus on the scans.
5. Ocular surface. A tear film good enough to measure from and to heal comfortably.
6. Eye and general health. Nothing active going on in the eye, and no medical condition that changes the risk.

Key takeaways: these six tell you whether an assessment is worth booking. They cannot tell you the answer. Only examination and scanning of your own eyes can do that, and the practice you book with should be willing to tell you no.

Age: when you are old enough for LASIK, and when it stops being the answer

Why turning 18 is not the green light

Eighteen is only the legal minimum. The clinical one comes later, and it is not about maturity.

Short-sightedness often keeps progressing into the early twenties. Treat a prescription that is still moving, and the cornea gets reshaped for a number the eye has already left behind. Your vision drifts back, and you have less cornea left to work with. At Pure Sight, LASIK is generally considered from around 21, with a prescription that has held steady.

What this means for you: stability is demonstrated, not assumed. If your glasses changed in the past year, bring the record of it.

The 40s: presbyopia changes the question

Standard LASIK corrects distance vision. It does nothing to prevent presbyopia, the age-related stiffening of the natural lens that puts reading glasses on almost everyone from the mid-forties. A short-sighted 46-year-old who has LASIK for distance can end up swapping one pair of glasses for another.

PRESBYOND is built for this. It uses the same LASIK platform to create a corneal profile with an extended blend zone, so both eyes work together across distance, screen, and reading range.

When a cataract makes lens surgery the better option

If the natural lens has started to cloud, reshaping the cornea treats the wrong structure. The blur is coming from behind the cornea, not from it. Cataract surgery or refractive lens exchange deals with the real problem and corrects the refractive error at the same time. Which is why the lens gets examined at a laser assessment, not only the cornea.

Is there an upper age limit?

No fixed one. The limits are the clarity of your natural lens and the health of the rest of the eye. From roughly 50 onwards, lens-based options become relevant more often, because they deal with the ageing lens as well as the prescription.

Your prescription: range and stability

How much short-sightedness, long-sightedness and astigmatism can be treated

Every dioptre of correction costs corneal tissue, so the treatable range depends on the relationship between your prescription and your corneal thickness rather than a fixed number.

Low to moderate short-sightedness sits well inside laser range. Higher degrees tend to favour ICL, more so when the corneas are thin. The band for long-sightedness is narrower. Your own range gets confirmed at the assessment.

Can laser eye surgery fix astigmatism?

Yes. Regular astigmatism is routinely treated with laser vision correction, usually at the same time as short or long sightedness, and modern lasers correct both the amount and the axis.

The exception matters. Irregular astigmatism, the kind produced by keratoconus or corneal scarring, is a different problem entirely. The cornea is not misshapen in a predictable way, it is unstable or damaged, and a laser is not the answer. That is a case for cross-linking, specialty contact lenses or an implanted lens.

Does it work for long sightedness?

Yes, though the range is narrower than it is for short sightedness. Timing is the complication. Long sighted people notice reading trouble earlier, so by the time many of them book an assessment, presbyopia is already part of the picture. Higher degrees are often better served by refractive lens exchange.

Why a stable prescription matters

What we are looking for is a year or two without meaningful change. Your optometrist’s old records help here, since they show a trend instead of one reading on one day. Bring them along, or ask for them to be sent across.

Your corneas: thickness and shape

What corneal thickness has to do with it

LASIK works by removing tissue. A femtosecond laser lifts a thin flap, an excimer laser reshapes the layer underneath, and the flap is laid back down. Thickness is measured by pachymetry, which simply means measuring how thick the cornea is.

What matters is what is left afterwards. The untouched tissue beneath the treatment is the residual stromal bed, and it has to stay above a safe minimum so the cornea keeps its strength. Go below it and the cornea can slowly bulge forward over the following years, a complication called ectasia. Thickness therefore caps the prescription that can be treated, which is why two people with identical glasses get different answers.

Topography and tomography: mapping the shape

Corneal topography maps the curve of the front surface. Corneal tomography goes further and builds a three-dimensional map, taking in the back surface and the thickness right across the cornea. Pure Sight adds epithelial mapping of the thin outer layer on top of that.

The back surface is the one that gives things away. An early cone often shows up there first, while the front still looks normal and the patient still reads 6/6 with glasses. A subtle irregularity counts for more than a thin reading on its own. Thinness is a known quantity and you can plan around it. Instability is not.

Keratoconus and suspect corneas

Keratoconus is progressive thinning and bulging of the cornea into a cone shape. LASIK is not performed on a cornea with keratoconus, or on one showing early or subclinical signs of it, because it removes tissue from a cornea that is already weakening.

That is not where the conversation stops. The usual order is to stabilise the cornea first with corneal cross-linking, which uses riboflavin drops and controlled ultraviolet light to strengthen the collagen bonds and stop the condition progressing. The prescription gets dealt with after that, usually with ICL surgery or specialty contact lenses. Cross-linking for documented progressive keratoconus attracts a Medicare benefit (MBS item 42652), which elective refractive surgery does not.

What this means for you: if you have been turned away before over a suspect cornea, the next step is a detailed tomographic assessment and a plan built around your own eyes.

If your corneas are too thin for LASIK

PRK is the main alternative. It reshapes the same tissue without creating a flap, which is why it suits thinner corneas, surface irregularities and people whose work or sport carries a risk of a knock to the eye. The end result is comparable to LASIK, but recovery is slower: two to three days of discomfort while the surface heals, then vision settling over the following weeks. ICL is the other option, and it leaves the cornea untouched entirely.

One assumption worth correcting: SMILE Pro is not the thin-cornea solution. It is flapless and preserves more corneal nerves, but it still removes tissue from within the cornea. If you are not suitable for LASIK, you will generally not be suitable for SMILE Pro either.

Dry eye and the surface of your eye

Dry eye gets in the way twice over, and both are easy to underrate.

First, measurement. An unstable tear film throws out the corneal surface reading, so the scans your surgical plan is built on are less reliable than they look. Treat the surface, measure again, and the numbers often move.

Second, comfort. Laser vision correction cuts corneal nerves. Dryness commonly increases for weeks to months afterwards, and starting out with a dry, inflamed surface makes that stretch worse. Meibomian gland dysfunction is the usual culprit: the oil glands in the eyelid block, tears evaporate too fast, and it goes unnoticed.

So the ocular surface is assessed and treated before a decision is made, not after. Dr Jonathan Yip, a therapeutically endorsed optometrist, leads the dry eye clinic at Pure Sight and plays a central role in refractive surgery screening, so the person assessing your tear film is the person who treats it. Options include intense pulsed light, low light therapy, Blephasteam and punctal plugs. Where dry eye is significant and persistent, ICL is sometimes the better recommendation, because it does not cut corneal nerves.

Pupil size, night vision and the way you use your eyes

Pupils that open wide in the dark can reach past the treated zone of the cornea, and light coming through that edge scatters. Halos and starbursts around headlights are common for a while after any laser procedure and usually settle down. A large pupil combined with a higher prescription does raise the odds of them hanging around. If you drive at night for a living, say so at the assessment. It does change the recommendation.

Sport and occupation count too. Contact sport and martial arts carry a risk of a blow to the eye, which argues for a flapless procedure. Aviation, defence and parts of the emergency services apply their own vision standards, and some specify which refractive procedures they accept and how long you must wait afterwards. Check with the relevant authority before booking surgery, not after.

General health, medications and pregnancy

Most general health conditions are assessed individually rather than treated as automatic exclusions. The ones that come up:

• Autoimmune and connective tissue disease. Rheumatoid arthritis, lupus or Sjögren’s affect healing and the ocular surface. Well controlled is a different conversation from active.
• Diabetes. Stable and well controlled is usually workable. Blood sugar that is not well controlled moves the prescription about and slows healing, and any diabetic retinal changes need looking at in their own right.
• Glaucoma. Glaucoma that is not under control, or significant optic nerve damage, generally rules out elective corneal surgery. Corneal thickness also changes how your eye pressure readings should be read, and that matters for the rest of your life.
• Active ocular inflammation. Uveitis or keratitis has to be quiet and stable first.
• Herpes simplex keratitis. A history of it is a genuine caution, because surgery can trigger reactivation.
• Medications. Some affect healing or tear production. Bring a full list, including eye drops and anything over the counter.
• Pregnancy and breastfeeding. A reason to defer, not to give up. Hormonal shifts alter the prescription and the tear film, so measurements taken now will not represent the eye in six months.

Who should not have LASIK

LASIK is not appropriate if you:

• have keratoconus, or scans showing early or suspect corneal changes
• have corneas too thin for a safe residual stromal bed at your prescription
• have a prescription still changing year to year
• have significant untreated dry eye or meibomian gland dysfunction
• have active eye inflammation or infection
• have uncontrolled glaucoma or poorly controlled diabetes
• are pregnant or breastfeeding, for now
• expect a perfect, permanent, glasses-free result in every situation for the rest of your life
• have not had your corneas properly measured

The last two are not clinical, and they disqualify people just as reliably as the first seven. None of these closes the door on vision correction itself. Several of them simply point at a different procedure.

What if you are not suitable for LASIK? Your alternatives

PRK. Surface treatment, no flap. Suits thinner corneas, surface irregularities and higher-impact occupations. Comparable end result, longer recovery.

SMILE Pro. Flapless lenticule extraction through a small incision, preserving more corneal nerves, which may mean less post-operative dryness. Needs a prescription above a minimum degree so the lenticule comes out intact, and it is not a substitute where LASIK is ruled out on thickness.

PRESBYOND. For patients from 40 addressing presbyopia rather than only distance vision.

ICL surgery. A collamer lens implanted inside the eye, cornea untouched. Often the most suitable option where the prescription is higher, the corneas thinner or irregular, or dry eye is established. It is removable and exchangeable, and the ICL Viva extends the range to presbyopia. Our comparison of LASIK and ICL surgery covers how that decision is actually made.

Refractive lens exchange. Swaps the natural lens for an intraocular lens. Usually considered from around 45 to 60 and over, for higher long sightedness, and where cataract is coming anyway.

Non-surgical options. Orthokeratology and specialty contact lenses remain reasonable answers. Being told no to surgery is not the same as being told nothing can be done.

What happens at a suitability assessment at Pure Sight

Allow about two hours. Long-sighted and complex cases sometimes run longer.

Initial screening is carried out by our refractive-trained orthoptists and consulting optometrists: refraction, corneal topography and tomography, epithelial mapping, pachymetry, tear film assessment and pupil measurement. Your pupils are then dilated so the lens and retina can be examined properly. Dilation blurs your vision for four to six hours, so arrange a lift or plan to wait it out. Dr Chiu reviews the results and goes through the options with you.

Take your contact lenses out first. This is the single most common reason an assessment has to be repeated. Lenses mould the cornea, and a moulded cornea gives false readings. Stop soft lenses at least 48 hours before your appointment. Stop hard or rigid gas permeable lenses for one week per year of wear, to a maximum of four weeks.

You will also need a current referral from your GP or optometrist, and it is worth bringing your old prescription records. You leave with a clear answer about your own eyes, the procedures they are suited to, and a written quote.

Why choose Pure Sight Eye Surgeons for LASIK eye surgery in Sydney

The value of an assessment depends on what the person doing it can offer you afterwards. Pure Sight performs LASIK, SMILE Pro, PRK, PRESBYOND, ICL and refractive lens exchange, so a recommendation can be made across the whole range. If your corneas rule out one procedure, you are assessed for the others.

Dr Alison Chiu, Specialist Eye Surgeon. FRANZCO, PhD, MBBS (Hons), BMedSc (Hons I), Grad Dip Refractive Surgery. Dr Chiu has a special interest in cataract surgery, including refractive and complex cases, and in refractive vision correction. She trained in ophthalmology at Sydney Eye Hospital, with subspecialty training at Macquarie University Hospital and an academic qualification in refractive surgery. Find her on Instagram, LinkedIn, Facebook and TikTok.

Dr Jonathan Yip, Consulting Optometrist. BOptom (Hons), BVSci. A therapeutically endorsed optometrist whose two named areas are dry eye management and refractive surgery screening. For a candidacy assessment, that combination is practical rather than decorative: a dry eye finding becomes a treatment plan and a remeasurement rather than a flat no.

Dr Adam Plant, Retinal and Cataract Surgeon. FRANZCO, PhD (Diabetic Retinopathy), BMed (Distinction). Subspecialty training and practice in retinal disease, vitreoretinal surgery and complex cataract surgery.

Dr Joanne Teong, Ophthalmologist. FRANZCO, MBBS, BA/LLB. Comprehensive ophthalmic care with a focus on medical retina, glaucoma and cataract surgery.

Having retinal and glaucoma care in-house matters more than it sounds. Higher short sightedness carries a raised lifetime risk of retinal problems, and corneal thickness changes how your eye pressure readings should be read for the rest of your life. Both are things to examine before an elective procedure, not discover after one.

Assessments are held at our consulting rooms in Paddington and Richmond. Laser procedures are performed at our laser suite in the Sydney CBD.

Paddington: 25 Norfolk Street, Paddington NSW 2021

Richmond: 135 Windsor Street, Richmond NSW 2753

Book a personalised vision assessment.

Further reading

• LASIK eye surgery
• ICL surgery
• Keratoconus
• Your first visit: what to expect

Medical references

• Healthdirect Australia. Keratoconus
• Austroads. Assessing Fitness to Drive: vision and eye disorders
• MBS Online. Item 42652, corneal collagen cross-linking
• Ahpra. Guidelines for advertising a regulated health service
• Centre for Eye Research Australia. Keratoconus
• NSW Health. Keratoconus referral criteria

---

This article is general information and is not a substitute for individual clinical advice. Suitability for any vision correction procedure can only be determined by examination and measurement of your own eyes.