Eyes with visually significant cataracts or that have had cataract-induced refractive shifts should not be considered for LVC.⁴³

Because PRK can alter corneal thickness and hysteresis measurements, and therefore intraocular pressure (IOP) accuracy, it should be avoided in unstable glaucoma. However, many surgeon’s have successfully performed PRK on glaucoma suspects and even those with controlled mild-to-moderate glaucoma. That is why most surgeon’s believe PRK in controlled glaucoma is an option after informed consent.⁴⁴

The greatest consideration in LVC is that of corneal thickness and integrity. At-risk eyes due to thin corneas, forme fruste keratoconus, and keratoconus should be found in preoperative screening and excluded from candidacy. In therapeutic cases of stable keratoconus or eyes that have been cross-linked, PRK has been successfully done to alleviate some of the refractive error and treat the corneal irregularities. Although corneal ectasia and keratoconus are more likely to occur after LASIK, they have occurred after PRK. Thinner corneas, keratoconus, and forme fruste keratoconus can lead to complications after PRK surgery. These complications may result in the need for additional therapeutic surgery.⁴⁵,⁴⁶,⁴⁷

Uncontrolled diabetes, pregnancy, nursing mothers, and certain medications such as amiodarone, isotretinoin, sumatriptan, and others can cause unstable refractive error, and therefore patients should not have PRK while on these medications or dealing
with these conditions. In that regard, any unstable refractive error case should be advised against surgery.⁴⁸,⁴⁹

PRK remains the best LVC option for many eyes, which have stable mild corneal scars from trauma, keratitis, or prior refractive surgical cuts like in RK. However, significant central corneal scars should not be lasered, especially if located in the posterior two thirds of the corneal stroma.⁵⁰,⁵¹,⁵²

As early as 1992, Seiler et al. noted potential complications in patients with autoimmune disease and considered it an absolute contraindication. Any type of active connective tissue disease (e.g., rheumatoid arthritis), or active autoimmune disease (i.e., lupus), is not an option for an elective procedure like PRK. These conditions affect the body’s ability to heal. However, inactive or controlled connective tissue disease is a controversial issue.⁵³,⁵⁴

If patients have severely dry eyes, PRK may exacerbate this condition. This may or may not resolve with time and healing. Severe eye dryness may delay healing of the surgery. It may result in poor vision after PRK, which may be permanent.⁵⁵

Patients with poorly controlled diabetes can be a challenge prior to surgery in obtaining a stable refraction and after surgery have risk of poor healing and aberrant outcomes.⁴⁹,⁵⁶

Patients with active eye infections or inflammation of the eye, such as recent herpes eye infections, should not be considered as candidates for an elective procedure like PRK.⁵⁷

The surgeon should consider systemic medications (i.e., Accutane or isotretinoin, Imitrex or sumatriptan, or Cordarone or amiodarone hydrochloride) the patient is taking. The surgeon should also consider any systemic or ocular condition that may predispose the eye to scarring or infection such as connective tissue disease, keloid formers, prior herpes simplex keratitis (HSK), ocular rosacea, and other causes of corneal neovascularization. If the patient’s vision has not been stable and they have signs of increasing or unstable nearsightedness, eye disease, eye abnormality, previous eye surgery, or injury in the treatment area of the eye, PRK should not be considered an option. With refractive error that is outside the range of the surgeon’s laser-approved range, it is not known if PRK is safe and effective outside those limits. Some surgeon’s consider reducing but not elimination of refractive error as an option in select patients with appropriate informed consent. Re-treatments carry additional risks and should be discussed with the patient. It is possible following PRK treatment that patients can have reduced contrast sensitivity and will find it more difficult to see in conditions such as very dim light, rain, snow, fog, or glare from bright lights at night. A patient with a family history of thinning of the cornea or other degenerative corneal disease (i.e., keratoconus, pellucid marginal degeneration, Fuchs corneal dystrophy, granular corneal dystrophy (Types 1 and 2), and lattice corneal dystrophy) may not be a good candidate for PRK.⁵⁸,⁵⁹

If the patient has a systemic disease that may affect wound healing, such as uncontrolled autoimmune or connective tissue disease, or uncontrolled diabetes, then it is imperative for the physician and the patient to acknowledge and document those risks and document those discussions and the potential risks and the issues with outcomes with the patient.

If the patient has an immunocompromised status or takes medications that may result in a weakened immune system, such as antimetabolites, which can increase the risk of infection, then discussion and education to the patient need to be taken prior to surgical intervention.⁶⁰

If a patient is taking or has taken the drug isotretinoin (Accutane), this can increase the risk of dry eye and may affect wound healing. While not an absolute contraindication, it does need to be documented as to the risks before proceeding.⁶¹

Keloid formers were once thought to be absolute contraindications, but recent studies have shown selective treatment of these patients with PRK can be considered with appropriate informed consent and considered on a case-by-case basis.⁶²,⁶³

Herpes simplex or herpes zoster infection that has affected a patient’s eyes may be at higher risk for reactivation of the disease. Prior HSK cases may be considered for surgery with informed consent and prophylactic oral antiviral therapy on a case-bycase basis.⁵⁷

Controlled glaucoma does not predispose the patient to additional risks; however, uncontrolled glaucoma is considered an absolute contraindication as mentioned earlier.⁴⁴,⁶⁴

If the patient has mild-to-moderate dry eye, PRK may increase the risk of worsening dry eye. Hyperopic treatments may create more issues than myopic treatments; however, both have been shown to exacerbate ocular surface disease.⁵⁵,⁶⁵,⁶⁶,⁶⁷

Ocular surface health should be closely examined to diagnose significant dry eye disease, corneal warpage from contact lenses, and other surface irregularities like epithelial basement membrane dystrophy. PRK is an option for those with controlled dry eye disease. Theoretically, because less tissue is removed than with LASIK, less corneal nerve disruption occurs, and therefore less dry eye effects have been suggested. However, research has shown the two procedures to be more equal in dry eye outcomes than previously thought. This study, however, only observed the first 3
months after surgery and did not look at long-term outcomes. Other transient and permanent causes of unstable or irregular topography such as contact lens warpage and anterior corneal dystrophies should be diagnosed and managed well before scheduling PRK surgery.⁶⁷

Amblyopes may consider PRK but should be appropriately informed and consented to the possibility of a complication, which may cause them to become solely dependent on the amblyopic eye. Similarly, monocular patients can proceed with PRK, but only after thorough counseling and informed consent about the relative risks and benefits. The patient with binocular anomalies requiring prism must be advised that they will still need prism correction after PRK.⁶⁸

Patients should be at least 18 years of age with a stable refractive error and realistic goals for surgery. As mentioned before, patients under the age of 18 may be considered for surgery as an off-label procedure and on a case-by-case basis. PRK has been successfully done on children in anisometropic conditions and other circumstances. The patient’s personality and visual goals should be strongly considered to ensure they do not expect more than the surgery can provide for them. If they have never been satisfied with the visual performance of glasses or contacts, then there is a likelihood that they will not be pleased with the outcome of PRK.⁶⁹,⁷⁰,⁷¹,⁷²,⁷³

Despite labeling in the patient information booklet, there have been various opinions on the risk of pacemakers interfering with laser instrumentation. However, the National Institute of Health (NIH) released in 2019 that the current body of evidence and our concomitant experiences illustrate a low risk of complications in patients with cardiac implantable electronic devices during refractive surgery. For this reason, most surgeon’s do not deter these patients from proceeding with surgery. However, it is still worth discussing with your patient and their primary care provider because of the labeling issues.⁷⁴

Contact lens-induced corneal warpage can be resolved by discontinuing contact lens wear before preoperative examination. The FDA preoperative guidelines recommend that soft contact lens wearers discontinue lens wear for at least 2 weeks before examination and treatment. Typically, toric and rigid gas permeable (RGP) lenses take longer to establish stability after discontinuing and therefore the surgeon may have extended criteria for these lenses.⁸³

A thorough health history should be taken to ensure that the patient is not at increased risk for surgery based on current health diagnoses, past family medical and ocular history, current and past medications, or any allergies to medications.⁸⁴

Uncorrected visual acuity (UCVA) and best corrected visual acuity (BCVA) should be recorded to prove that the surgery is warranted. This also shows documentable proof of the potential for improved uncorrected acuity after surgery.

Although controversial, corneal thickness readings should be high enough to allow for a postoperative residual stromal bed of at least 250 µm, according to the most widely accepted guidelines. A residual thickness of 250 µm is a customary target; however, there is no substantive scientific evidence to support that single number. To that point, eyes with more than 250 µm of residual stromal bed have developed ectasia after LASIK while eyes with much less have remained stable.¹¹ Most lasers remove approximately 15 to 18 µm of tissue per diopter of ametropia. The thickness map, as imaged by Orbscan or Pentacam, should also be uniform throughout the cornea to ensure that there are not thin areas, which could increase the risk of iatrogenic keratoectasia. Abnormally thick corneas could indicate corneal edema and potential for unrecognized disease. More recently, Santhiago has suggested evaluation of the percent tissue altered in LVC.⁸⁵,⁸⁶,⁸⁷

Keratometry values should be measured so that PRK does not excessively flatten or steepen postoperatively. For myopic treatments, laser ablation flattens the keratometry value at a rate of 0.7D per each 1D of myopia. Hyperopic treatments steepen at a 1:1 ratio. Most sources recommend postoperative keratometry values not to be flattened less than 36.0D or steepened greater than 48.0D. However, again with appropriate informed consent, keratometry readings post-PRK outside these ranges can be considered on a case-by-case basis.⁸⁸

Assessing the front and back surface corneal topography by either the Orbscan or Pentacam has become the standard of care in refractive surgery evaluations. Corneal topography, along with the magnitude of the refractive error, is important in determining whether corneal laser surgery (LASIK/PRK/laser epithelial keratomileusis [LASEK]) will lead to abnormally steep or abnormally flat postoperative corneal curvature, which can affect the quality of postoperative visual acuity.⁴⁹,⁸⁹

Standard slit lamp examination for screening is recommended in all patients.

Accurate preoperative IOP readings are crucial as they can be altered by thinning from the laser ablation. If the patient has a family history of glaucoma, a more detailed analysis such as optical coherence tomography (OCT) of the optic nerve should be considered prior to surgical intervention.⁹⁰,⁹¹,⁹²

Corneal hysteresis is one option that has been suggested as a screening tool in glaucoma suspects and can serve as a predictive factor in keratoconus and postsurgical ectasia.⁹³

A careful manifest refraction with binocular balance is essential for the best outcomes in refractive surgery.

Cycloplegic refraction is designed to rule out any accommodation that may skew the manifest refraction. Note that it is best to have topography and keratometry done before cycloplegia as the drops may induce surface changes. Cycloplegic refractions are not required but suggested in those patients with more accommodative amplitudes such as younger patients, patients with hyperopia, hyperopia with astigmatism, high myopia, high myopia with astigmatism, and mixed astigmatism.⁹⁴

The vertex distance must also be measured carefully since surgical alterations of the corneal refraction are necessarily performed at the corneal plane. Fortunately, this information is usually incorporated into the laser system software and does not
typically have to be measured at each preoperative examination. Once established in a refractive lane and standardized throughout the clinic, those parameters should remain constant.⁵⁷

Most surgeon’s elect to do both eyes on the same day. There can be reasonable arguments on which eye to do first based on eye dominance. Eye dominance is important in patients for whom the surgeon chooses monovision as an option as this can reduce the potential for re-treatment when monovision fails. Females tend to prefer monovision over males, and the preferred eye is the dominant eye for distance in most patients; however, some patients prefer their dominant eye to be corrected for near. Contact lens trials are beneficial in determining patient preference because patients vary over which should be targeted as the reading eye based on eye dominance, habits, and hobbies.⁹⁵,⁹⁶,⁹⁷,⁹⁸,⁹⁹,¹⁰⁰,¹⁰¹

Various technologies have been utilized to measure the pupil and higher-order aberrations (HOA) prior to refractive surgery. Significant advances in refractive surgery outcomes have resulted from wave front systems that measure dynamic pupil changes and HOA. Before this technology, most of the postoperative night vision complaints, glare, and halos were due to uncorrected HOAs and large pupils. Current technology has improved the ablation profiles to minimize HOA and induced dysphotopsias.¹⁰²,¹⁰³,¹⁰⁴,¹⁰⁵,¹⁰⁶

Many surgeon’s decrease bacterial load on the eyes by having the patient start topical prophylaxis and discontinuance of all facial products and cosmetics for at least one day prior to surgery. Lid scrub use is also a potential strategy especially with patients who have lid margin disease.¹⁰⁷,¹⁰⁸

Vitamin C has proven in studies to prevent postoperative haze and enhance healing. This may be added to the preoperative regimen, however some physicians choose to initiate this option postoperatively.¹⁰⁹,¹¹⁰

Omega 3 supplements, topical cyclosporine or lifitegrast, or punctal plugs may be added before treatment to enhance the ocular surface prior to surgery or considered postoperatively.¹¹¹