Cataract surgery after radial keratotomy (RK): what changes in planning?Cataract surgery after RK: what changes?

What changes when cataract surgery follows RK?

RK was an operation for short-sightedness that used deep, spoke-like cuts in the cornea (the clear window at the front of the eye) to flatten its centre. Cataract surgery removes the cloudy natural lens behind the iris and replaces it with an intraocular lens implant (IOL). It does not replace that corneal window.

Two separate problems therefore need assessment: the focusing prescription, which an IOL and glasses can often improve, and optical irregularity, which can cause ghosting, glare and reduced contrast even when the prescription is close to the intended target. A good result may still involve spectacles or a specialist contact lens.

The principles differ from cataract planning after LASIK, PRK or SMILE. Those operations also alter the cornea, but RK adds longstanding incision scars and greater concerns about changing shape and wound separation.

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Do all RK operations leave the same cornea?

No. Eyes may have four, six, eight, twelve, sixteen or more cuts. Some underwent extra cuts or repeat deepening, short-incision variations, additional curved or transverse astigmatic keratotomy (AK), or later laser surgery. Cuts could be made towards the centre (centripetal), away from it (centrifugal), or with two passes.

The number matters, but so do the depth, length and spacing of scars, the size and centration of the untouched optical zone, any cut entering that zone, and how each wound healed. A small or decentered clear zone can be particularly troublesome when the pupil enlarges in dim light. A four-cut eye with deep scars is not automatically simpler than an eight-cut eye.

More incisions usually leave less room between scars for cataract entry wounds. The surgeon maps the actual pattern rather than relying on the old operation name. Old records are useful, but examination and corneal imaging remain essential.

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Why can vision change from morning to evening?

The incised cornea can change shape during the day. Hydration and overnight swelling interact with its altered biomechanics. A common pattern is a flatter cornea and more long-sighted prescription in the morning, followed by steepening and a shift towards short-sightedness later. The amount and even the direction can differ between individuals; dry eye adds another source of variability.

The Prospective Evaluation of Radial Keratotomy (PERK) study followed people who underwent a standardised RK procedure. In a follow-up of 71 patients about 11 years after RK, 51% of first-operated eyes became at least 0.50 dioptre more short-sighted between morning and evening. Astigmatism changed by at least 0.50 dioptre in 31%. These are findings from a particular historic RK protocol, not the predicted fluctuation rate after modern cataract surgery.

Tell the team when reading, driving or night vision is best or worst. Recording examination times, repeating measurements on different days, and comparing morning with afternoon when symptoms or readings suggest variability can reveal a pattern that one excellent-looking scan misses. Cataract removal does not remove this daily change.

How are the corneal surface and measurements checked?

Planning combines a careful refraction, optical biometry for eye length and lens power, and corneal topography or tomography for the central shape, astigmatism and irregularity. The two corneal surfaces, tear film, pupil size, scar position and any thinning or ectasia (progressive corneal bulging) can all matter. Ordinary keratometry samples a limited area and may not represent a small, very flat or uneven central optical zone.

Treating dry eye before final measurements helps remove avoidable noise. Contact lenses can also change the measured shape; the appropriate break from wear and repeat checks depend on the lens type and whether the cornea has stabilised.

Useful records include the original RK report, the prescription before RK, the stable prescription achieved afterwards, and later changes. For optometrists, dated refractions, their time of day, best spectacle-corrected acuity, topography maps and prior contact-lens performance are particularly helpful. A rigid or scleral lens trial can sometimes show how much blur comes from the cornea rather than the cataract.

The macula, retina, optic nerve, pressure and corneal endothelium, the inner cell layer, also need assessment. Previous high myopia or another eye condition may limit the outcome independently of RK. Irregular corneas can complicate pressure interpretation; apparently reassuring numbers should be assessed in context.

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Which lens formulas are used, and why compare several?

Post-RK calculations use methods designed or evaluated for altered corneas. Barrett True-K in RK mode, with history, partial history or no history as appropriate, is a common reference. The ASCRS post-refractive calculator has a separate RK pathway. Double-K methods, including modified Holladay 1 or SRK/T, separate the corneal information used for lens-position prediction from that used for focusing power. Standard Haigis has also performed usefully in RK studies; Haigis-L is a different method developed for laser-altered eyes and is not an interchangeable name.

A surgeon may compare several suitable calculations and a defensible combination rather than trust one output. In a 50-eye study, combinations of three or more selected formulas generally performed better than individual formulas. That does not make an unweighted average of any available formulas reliable: shared measurement errors remain shared errors.

Very flat corneas and unusually long eyes require particular caution. Measuring posterior corneal power or using total keratometry can help some formula–device combinations, but does not automatically improve every formula. Two 2026 studies reinforce that performance depends on the formula, corneal curvature and eye length; there is no universal winner.

Intraoperative aberrometry measures the eye’s optical power during surgery to help estimate the lens prescription. Its extra predictive value after RK is uncertain. In a prospective 52-eye study, 63.5% were within ±0.50 D of the prediction with Barrett True-K, compared with 48.1% using the Optiwave Refractive Analysis (ORA) system. A separate 47-eye study found similar accuracy between the two methods, with no statistically significant difference. These small comparisons do not show a consistent advantage over modern preoperative calculations.

The cornea’s hydration, pressure and shape during surgery can differ from their healed state, particularly after RK. A measurement at that moment therefore cannot be treated as the final prescription. Intraoperative readings may offer another piece of information, but do not remove the need for repeat preoperative measurements, suitable formulas and realistic expectations.

How often does a refractive surprise occur?

A refractive surprise means the final prescription differs from the planned prescription. It is not synonymous with a surgical complication, poor corrected sight or a need for another operation. Studies often report spherical-equivalent prediction error, which averages sphere and half the cylinder; this does not describe all astigmatism, ghosting or night-vision quality.

For a rough guide, several post-RK series using appropriate methods found about 50–75% of eyes within ±0.50 dioptre of target. That leaves roughly one-quarter to one-half outside that narrow range. Results outside ±1.00 dioptre are less frequent, but remain important. These are study ranges, not a personalised risk estimate or a pooled success rate.

• A 52-eye formula comparison reported 69.2% within ±0.50 D using no-history True-K or Haigis, and about 75–77% when suitable historical information was used.
• In a 50-eye study, one three-formula combination achieved 66% within ±0.50 D and 84% within ±1.00 D: 34% and 16%, respectively, were outside those ranges.
• An older 100-eye hospital series had poorer results overall. Its Haigis subgroup contained only 19 eyes: 52.6% were within ±0.50 D and 68.4% within ±1.00 D. Other formula subgroups did worse.

The studies differ in case selection, formula versions, measurement methods and follow-up, and should not be ranked as if they were a single trial. Even with excellent preparation, substantial long-sighted or short-sighted surprises can and do occur. Agreement between several calculations reduces uncertainty; it does not eliminate it.

Should the planned prescription be slightly short-sighted?

A modest myopic target is sometimes chosen because RK eyes can drift towards long-sightedness and some calculations have a hyperopic bias. The target must still match the patient’s needs, the fellow eye and the actual measurements. It is not a universal −0.50 D rule, and a built-in formula adjustment should not be inadvertently applied twice.

A mildly short-sighted result may make near tasks easier but can require distance glasses. Deliberately creating monovision, one eye for distance and the other for nearer tasks, needs particular discussion about depth perception, tolerance and existing fluctuating vision. No initial target can insure against decades of future corneal change.

How does RK change cataract wound placement?

Old RK wounds remain weaker than uncut cornea and can separate, or dehisce, during cataract surgery even decades later. The main entry wound and smaller side ports are planned to avoid crossing RK scars. Where the gap is too narrow for a safe corneal entry, a more posterior limbal or scleral tunnel approach may be preferable.

More cuts, deep or gaping scars, additional AK wounds and prior enhancements change the available space. Gentle instrument movement, controlled fluid pressure and careful checks for leakage matter. A supporting or closing suture may be needed; it can temporarily change astigmatism and affect when the final prescription is measured. Laser-assisted cataract surgery does not remove these constraints.

RK wound separation occurred in 8 of 100 eyes in one hospital series, including eyes with eight cuts. A separate 19-eye series using 3.2-mm corneal entries reported two separations, both among its six sixteen-cut eyes. These small, technique-dependent reports demonstrate the risk, not a universal 8% rate or a rigid incision-size recipe for every scar pattern.

Why are monofocal lenses usually the starting point?

A monofocal IOL is most commonly the appropriate choice after RK. It aims for one main focus and avoids deliberately adding multiple competing images to an already imperfect corneal optical system. Glasses for some tasks should be expected. A monofocal implant does not remove irregular astigmatism or guarantee freedom from glare.

A toric monofocal can be considered when a meaningful component of astigmatism is regular, central, repeatable and has a consistent axis across measurements. In a carefully selected 40-eye series, 73% had residual regular astigmatism of 0.50 D or less. This was an astigmatism outcome, not a measure of spherical lens-power accuracy.

A toric implant cannot cancel changing or irregular astigmatism and higher-order aberrations (the more complex distortions responsible for ghost images and starbursts). The toric lens guide explains this distinction.

If irregular astigmatism means a rigid gas-permeable or scleral contact lens may be needed afterwards, a toric implant can make the optical correction more complex. The contact lens and the fluid beneath it mask much of the astigmatism from the front of the cornea, but the implant’s cylinder (astigmatism) correction remains inside the eye and may become apparent as residual astigmatism. A contact lens with additional cylinder correction on its front surface, or glasses over the contact lens, may then be needed. This does not make fitting impossible, but likely future contact lens use should be discussed before choosing a toric IOL.

Can enhanced monofocal, EDOF or multifocal lenses be used?

Sometimes, in carefully selected eyes with sufficiently regular and stable central optics. Enhanced monofocal designs modestly extend intermediate focus; EDOF designs extend the usable focus range by different optical mechanisms. They are not all equivalent, and favourable results with one design do not establish suitability for another.

A retrospective Symfony EDOF study of 24 eyes in 12 post-RK patients reported improvement in unaided distance vision and satisfaction in seven of nine survey respondents. Visual follow-up averaged five months; the questionnaire was completed at a mean of six months. Conversely, a small mixed multifocal series reported disappointing distance results. A separate 14-eye trifocal series reported selected successes while still identifying glare and night-vision difficulties. A newer 2025 cataract/lens-replacement cohort also reported favourable one-year outcomes in a selected 22-eye RK subgroup receiving a diffractive trifocal lens. These small, non-randomised studies do not establish these lenses as the usual choice.

Diffractive multifocal and trifocal implants can add halos and reduce contrast on top of RK-related aberrations. Greater irregularity, unstable readings, severe pre-existing glare, limited corrected vision or retinal disease make this trade-off less attractive.

Anyone choosing an extended-focus or multifocal option needs to accept that visual quality may be suboptimal despite an apparently good prescription. Glasses, contact lenses or additional surgery, including IOL exchange, may be needed. Exchange has its own risks and cannot promise to fix distortion originating in the cornea.

What about IC-8 and the Morcher sulcus pinhole implant?

Small-aperture optics admit a narrower bundle of light rays and can reduce the effect of some corneal aberrations. They may be useful when an irregular cornea limits conventional optics. They do not reshape or stabilise the cornea, remove scars or make lens-power calculation unnecessary. A preoperative pinhole test, refraction and corneal imaging help assess potential; a good test is not a guarantee.

Potential trade-offs include less light reaching the retina, poorer vision or contrast in dim conditions, glare or halos, conspicuous floaters and sensitivity to centration. In an 11-eye XtraFocus series involving several causes of irregularity, eight patients were satisfied and two requested removal because of glare or distressing floaters. Those numbers are not an RK-specific complication rate.

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Will cataract surgery remove glare and halos?

It may reduce the component caused by the cataract, but RK scars, an uneven cornea and a small clear optical zone can continue to scatter or distort light. Larger pupils at night expose more peripheral irregularity, so a good daytime letter-chart result does not guarantee comfortable night driving.

Discuss existing halos, starbursts, overlapping images and low-contrast difficulty before choosing an IOL. An optometrist’s observations under different lighting conditions can be useful. Monofocal lenses minimise additional optical complexity; premium and small-aperture options have different trade-offs rather than a guaranteed solution to glare.

How long does the prescription take to settle?

Recovery can be more variable than after routine cataract surgery. Early corneal swelling and flattening may produce a temporary long-sighted result that moves back towards short-sightedness as the cornea recovers. A small 2026 series documented early flattening with partial recovery by five to six weeks; it did not establish a fixed settling time for every eye.

Repeated refraction and corneal maps over weeks to months may be needed before ordering final glasses or deciding on corrective surgery. Scar sutures, dry eye and daily fluctuation can delay a dependable endpoint. A prescription that looks stable at one time of day may still fluctuate at another.

Staging the two eyes can allow the first eye’s response to inform the second, although their scar patterns and behaviour may differ. Avoid assuming that an early unexpected prescription represents a permanent lens-power error.

What can be done if the result is not as planned?

First establish whether the problem is a stable prescription error, corneal irregularity, dry eye, capsule clouding, implant position or another eye condition. Several may coexist. Glasses may be enough for a regular error; rigid gas-permeable or scleral contact lenses can mask an irregular anterior corneal surface and may offer more improvement than further lens surgery.

For a stable focusing error, selected patients may be considered for a powered add-on lens, IOL exchange or corneal laser treatment. Exchange corrects the implant’s power or optical design; it does not repair the RK cornea. Additional surgery must also negotiate the old scars and carries risks.

Laser enhancement is not always safe or effective when the cornea is thin, markedly irregular, scarred or unstable. An acceptable surface and sufficient tissue are essential; PRK is not automatically safe simply because it avoids a LASIK flap. Corneal suturing or other specialist measures may help particular problems, but are not universal remedies. Cross-linking has limited post-RK evidence and is not a routine way to abolish fluctuation.

Some patients have no acceptable surgical correction of the irregularity short of corneal grafting. A graft may be considered for severe, visually limiting disease when other options are unsuitable, but brings prolonged recovery, possible rejection and further astigmatism. It is not an inevitable next step or a guarantee of glasses-free vision. Continuing optical correction may be the better choice.

If implant intolerance or exchange is being considered, discuss it before YAG laser opens the posterior capsule. An open capsule can make later exchange more complex, as explained in YAG capsulotomy and later IOL exchange.

A light-adjustable IOL is an emerging option in international practice: its power can be adjusted after implantation before the final lock-in treatments. In a 94-eye retrospective RK series, 88% were within ±0.50 D and 98% within ±1.00 D after the treatment course. There was no randomised comparison, only five eyes had sixteen cuts, and adjustments require sufficient settling, repeated visits and protective eyewear. It does not eliminate corneal aberrations or future drift; local availability and suitability need checking.

Lens exchange through a small incision

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What should be expected over the longer term?

The cataract itself does not return, but RK-related changes can continue. In the original eight-cut PERK study, 43% of eyes shifted at least 1.00 D towards long-sightedness between six months and ten years after RK. This is not a ten-year outcome after cataract surgery and cannot predict an individual’s future change.

Most modern post-RK IOL reports follow patients for months or a few years, so lifelong stability of premium or pinhole implants in this setting is not established. Later glasses changes, contact-lens refitting or treatment of posterior capsule clouding may be needed. Ongoing retinal, glaucoma and corneal review remains relevant, particularly with previous high myopia.

A successful plan balances improved cataract-related vision with an honest understanding that the cornea, and therefore visual quality and prescription, may continue to change.

What questions are worth asking before surgery?

• How much of my reduced vision comes from the cataract, and how much from the cornea or another eye condition?
• Are my central corneal measurements repeatable, including at different times of day?
• Which RK-specific calculations are being compared, and how far apart are their predictions?
• Why is the proposed lens and target suitable for my cornea and everyday needs?
• Where will the surgical wounds go, and might a suture or alternative entry be needed?
• What glasses or specialist contact lenses might I still need?
• If I have a refractive surprise or poor visual quality, which remedies are realistic, and which may not be safe?