Night vision and contrast after LASIK or PRK

You had LASIK or PRK, your daytime vision is sharp — maybe better than it has been in years — and then you drive home after dark and every headlight sprouts a halo, every streetlight throws off spokes of light, and the dim road ahead looks flatter and grayer than you remember. If that is you, you are not imagining it and you are not alone. Night-vision changes are one of the most commonly reported experiences after corneal laser refractive surgery, even when the surgery is, by every clinical measure, a success.

The short version: LASIK and PRK reshape the front surface of your cornea to correct your prescription, and that reshaping can slightly change how light comes to a focus — especially at the edge of a wide, dark-adapted pupil at night. For some people the result is halos, starbursts, glare, and a dip in low-light contrast. Modern wavefront-guided and wavefront-optimized treatments are designed to keep these effects small, and for most patients they fade over weeks to months as the cornea heals, dry eye settles, and the brain adapts. A minority have longer-lasting night-vision symptoms. A contrast sensitivity check is a functional signal you can track before and after surgery — not a diagnosis, and never a substitute for your surgeon.

What LASIK and PRK actually change on the cornea

Your cornea — the clear dome at the front of the eye — does roughly two-thirds of your eye's focusing. Both LASIK and PRK use an excimer laser to remove an extraordinarily thin, precisely shaped layer of corneal tissue, flattening the cornea to correct nearsightedness or steepening it for farsightedness. The optical goal is the same for both; what differs is how they get to the tissue. LASIK creates a thin hinged flap, lifts it, reshapes the bed underneath, and lays the flap back down. PRK removes the surface skin of the cornea (the epithelium) entirely, reshapes the exposed surface, and lets the epithelium grow back over the following days.

The reshaped region that does the correcting is called the optical zone, and it is finite — often around 6 to 6.5 mm across — surrounded by a blend or transition zone where the new curvature tapers into the untreated cornea. That geometry is central to the whole night-vision story: the middle of your cornea is precisely corrected, and the edges are a transition. In bright light, with a small pupil, you only ever look through the good central part. In the dark, you do not.

Higher-order aberrations, and pupil versus optical zone at night

Your glasses prescription captures the big, "lower-order" focusing errors: simple defocus and astigmatism. But eyes also have subtler distortions that no standard prescription can describe, called higher-order aberrations. Two matter most here: spherical aberration, where light through the edge of the pupil focuses at a different point than light through the center, and coma, an asymmetric smearing that turns a point of light into a little comet tail. Reshaping the cornea — particularly flattening the center relative to the periphery — tends to induce some spherical aberration, and any small off-center in the treatment can add coma.

Here is why night is different. In daylight your pupil is small, roughly 2 to 3 mm, and samples only the central, well-corrected optical zone, so your vision is crisp. After dark your pupil dilates to something like 5 to 7 mm, and now light also streams through the periphery and the transition zone, where the correction changes and the induced aberrations live. Villa and colleagues measured this directly: after successful LASIK, an objective index of halo disturbance under night conditions rose by a factor of about 2.15, with coma and spherical aberration among the main contributors (Villa and colleagues, 2007). Schallhorn and colleagues found that patients with larger pupils reported more glare and halos in the first three months after LASIK — but that this relationship faded and the symptoms had resolved by six months without affecting overall satisfaction (Schallhorn and colleagues, 2003).

The old worry that a dark-adapted pupil "bigger than the optical zone" guarantees night-vision problems was a real concern with the narrow ablations of early LASIK. Wider optical zones, aspheric and prolate-preserving profiles, and pupillometry screening have reduced that mismatch considerably. They reduced the problem; they did not abolish it, which is the honest through-line of this whole topic.

Halos and starbursts: light that does not all land in one place

A halo is a ring of light around a bright point; a starburst is a spray of radiating spokes. Both come from the same root cause: not all of the light from a bright source is landing in a single sharp focus. Some of it, bent slightly differently by the transition zone or by induced aberrations, spreads around the focused image as a glow or streaks. Against a dark night sky studded with a few very bright points — headlights, streetlights, brake lights — that spread is exactly when it is most visible.

This is the same family of optical artifact that people describe after cataract surgery with certain lens implants, where the source is the edge of an artificial lens rather than the cornea; we cover that distinct mechanism in halos and starbursts after cataract surgery. It is also a cousin of ordinary night-driving glare, where the disabling wash of bright light — as opposed to mere discomfort — is the real problem; our piece on disability glare unpacks that distinction. One thing worth noting: after refractive surgery the artifact is generated inside your own reshaped cornea, so the external fixes that help ordinary eyewear, such as anti-reflective coatings, address a different part of the light path and cannot undo a corneal source. The key reassurance is that these are optical phenomena, common in the early weeks, and usually not a sign the surgery failed.

The contrast sensitivity dip — and the recovery timeline

Contrast sensitivity is your ability to tell apart subtle differences in shading — the faint edge of a gray curb at dusk, a pale face against a dim background — rather than just reading tiny high-contrast black letters on white. It is the axis of vision most sensitive to exactly the things that follow surgery: induced aberrations and a disturbed tear film. That is why contrast can dip transiently even when your acuity line reads a proud 20/20, and why acuity alone can miss what you are feeling at night.

The typical timeline is reassuring. Symptoms and any contrast dip tend to be strongest in the first days to weeks, ease noticeably over the first one to three months, and largely settle by around three to six months as the epithelium heals, the tear film recovers, and the brain neuroadapts — learning to quiet stable, uninformative artifacts. PRK often lags LASIK a little in those first weeks because the surface takes longer to heal. And modern ablation profiles are not doomed to degrade contrast: a study of wavefront-optimized myopic LASIK found contrast sensitivity actually improved after surgery across patients, regardless of how deep the ablation went (Heralgi and colleagues, 2020). The balanced caveat is that recovery is typical, not universal — a minority of people retain some measurable reduction in low-light contrast, and their experience is real even when the averages look good.

Dry eye's quiet role

One of the biggest and most under-appreciated contributors to post-surgery night vision is not the cornea's shape at all — it is its surface. Creating a LASIK flap, and to a lesser extent removing the epithelium in PRK, temporarily interrupts the corneal nerves that drive tear production and reflex blinking. The result is that nearly every LASIK patient has some degree of dry eye in the early postoperative period, and in a meaningful subset it is significant enough to affect vision quality (Shtein, 2011). A dry, irregular tear film scatters light and blurs the image in the moments between blinks, which shows up as fluctuating vision, glare, and reduced contrast — and it is worst precisely when you blink least, such as during concentrated night driving or staring at screens. The good news is that post-surgical dry eye is often treatable and time-limited, so some night-vision complaints improve simply as the ocular surface recovers. This is why a good surgeon evaluates your tear film, not just your refraction.

Who is at higher risk

Some people are more likely to notice night-vision symptoms than others:

• Large dark-adapted pupils relative to the optical zone, especially with the narrower ablations used in older procedures.
• Higher preoperative prescriptions, which require removing more tissue and produce a larger shape change and more induced higher-order aberrations.
• Pre-existing dry eye or a marginal tear film before surgery.
• Off-center or asymmetric healing, which can add coma.

Modern preoperative screening — pupillometry, corneal topography, wavefront analysis, wider optical zones, and femtosecond-laser flaps — exists partly to flag and reduce these risks. But these are risk factors, not verdicts: most people who carry them still do well. They are reasons to have a careful pre-surgery conversation, not reasons to expect a bad outcome.

A contrast sensitivity test is a screening signal of one slice of visual function. It cannot diagnose a surgical complication, measure your aberrations, or tell you whether night-vision symptoms will resolve. New, worsening, or persistent symptoms after LASIK or PRK belong with your surgeon, not a home screen. This article is educational and does not replace an eye exam or a surgical consultation.

What to do next

If you are still deciding on surgery, ask your surgeon three concrete questions: how big is my dark-adapted pupil compared with the planned optical zone, what is my dry-eye status and how will it be managed, and am I a candidate for wavefront-guided or topography-guided treatment. If you are recently post-op, give the recovery timeline time to work, keep up any prescribed lubrication, and report symptoms that are severe or not improving rather than waiting silently.

Either way, it helps to track the functional trend rather than trusting memory. You can take a free contrast sensitivity test before surgery and again afterward — the comparison is only meaningful if you use the same device, the same screen settings, and similar room lighting each time, so try to keep those constant. Bring the trend, and any night-vision symptoms, to your surgeon. A screening signal points you toward the right conversation; it never replaces one.

References

• Villa, C., Gutiérrez, R., Jiménez, J. R., & González-Méijome, J. M. (2007). Night vision disturbances after successful LASIK surgery. British Journal of Ophthalmology, 91(8), 1031–1037. An objective index of night-time halo disturbance increased roughly 2.15-fold after successful LASIK, with coma and spherical aberration among the main contributors.
• Schallhorn, S. C., Kaupp, S. E., Tanzer, D. J., Tidwell, J., Laurent, J., & Bourque, L. B. (2003). Pupil size and quality of vision after LASIK. Ophthalmology, 110(8), 1606–1614. Larger pupils were associated with more glare and halos in the first three months after LASIK, but the symptoms had resolved by six months without reducing patient satisfaction.
• Heralgi, M. M., Kavitha, V., Dwivedi, M., Preethi, V., Roopasree, B. V., Rajashekar, J., & Deokar, A. (2020). Study of change in contrast sensitivity in relation to depth of ablation after wavefront optimized myopic laser-assisted in situ keratomileusis. Indian Journal of Ophthalmology, 68(12), 2975–2980. Contrast sensitivity improved after wavefront-optimized myopic LASIK across patients, irrespective of stromal ablation depth.
• Shtein, R. M. (2011). Post-LASIK dry eye. Expert Review of Ophthalmology, 6(5), 575–582. Nearly all LASIK patients develop some dry eye in the early postoperative period, and moderate-to-severe cases can meaningfully affect vision quality and comfort.