What are the potential causes of blurry vision in a patient after Photorefractive Keratectomy (PRK) laser surgery?

Causes of Blurry Vision After PRK Laser Surgery

Blurry vision after PRK is most commonly caused by normal epithelial healing (lasting days to weeks), followed by residual refractive error, corneal haze, dry eye syndrome, and visual aberrations—with serious complications like corneal ectasia or infection being rare but critical to exclude. 1

Expected Post-Operative Course

Vision is typically poor for some time after PRK, with activities like driving potentially impossible for weeks. 1 This differs fundamentally from LASIK because PRK removes the entire central corneal epithelium, requiring complete re-epithelialization before functional vision returns. 1, 2

• Early post-operative period (first week): Uncorrected visual acuity averages 20/25 at 1 week, significantly worse than LASIK (20/20), due to ongoing epithelial healing rather than refractive error. 2
• One month post-operatively: Vision typically improves to 20/20 as epithelium stabilizes. 2
• Six months and beyond: Refraction, corneal haze, and topography should stabilize; retreatment should not be considered before this point. 1

Common Causes of Blurry Vision

Residual Refractive Error

• Undercorrection or overcorrection occurs in a minority of patients and represents symptomatic deviation from intended refractive outcome. 1
• Regression of effect is common, particularly with higher degrees of myopia, causing gradual return of blur over months. 1
• Induced regular or irregular astigmatism can develop from improper axis alignment during surgery or healing irregularities. 1

Corneal Haze and Scarring

• Corneal haze (early or delayed onset) develops from subepithelial fibrosis and directly impairs visual clarity. 1
• Haze is more common with higher corrections and can be permanent if severe. 1
• Retreatment in the presence of anything more than mild corneal haze should be carefully considered as it increases risk of recurrent haze. 1

Dry Eye Syndrome

• Development or exacerbation of dry eye symptoms is extremely common after PRK due to corneal nerve disruption affecting tear production. 1
• Dry eye causes fluctuating vision, particularly with blinking, and chronic ocular surface irritation. 1
• Decreased corneal sensitivity from nerve damage compounds the problem by reducing reflex tearing. 1

Visual Aberrations

• Glare, starburst, or halo effects (especially at night) occur from optical zone size mismatches with pupil diameter or from irregular healing. 1
• These aberrations can be transient or permanent and represent higher-order aberrations not measured by standard visual acuity testing. 1
• Decreased contrast sensitivity impairs functional vision even when Snellen acuity appears adequate. 1
• Patients with starbursts typically have high forward and backward light scatter from corneal haze, while halo phenomena correlate with large pupillary diameters and hyperopic shifts. 3

Serious Complications Requiring Urgent Evaluation

Infectious or Inflammatory Keratitis

• Corneal infiltrates, ulceration, melting, or perforation (sterile or microbial) present with severe pain, redness, and photophobia—not just blur. 1
• Central toxic keratopathy causes acute vision loss with characteristic corneal findings. 1
• Reactivation of HSV keratitis can occur in susceptible patients. 1

Corneal Ectasia

• Progressive corneal steepening manifests as worsening irregular astigmatism and progressive myopia months to years after surgery. 1
• This devastating complication occurs from unrecognized forme fruste keratoconus or excessive tissue removal. 4, 5
• High or difficult prescriptions with multiple retreatments are major avoidable risk factors. 4

Loss of Best-Corrected Visual Acuity

• Loss of BCVA occurs in approximately 0.6% of eyes (range 0-3%) and represents permanent damage to visual potential. 1
• This can result from irregular astigmatism, scarring, or ectasia. 1, 4

Corticosteroid-Related Complications

• Ocular hypertension, glaucoma, or cataract can develop from prolonged topical corticosteroid use during the healing phase. 1
• These complications cause gradual vision loss if unrecognized.

Other Causes

• Recurrent corneal erosion causes episodic blur and pain from unstable epithelium. 1
• Corneal neuralgia presents with chronic pain and may be associated with visual disturbances. 1
• Anisometropia (unequal refractive error between eyes) causes binocular vision problems. 1

Clinical Approach

Evaluate timing of blur onset: Immediate post-operative blur is expected and resolves with epithelial healing, while delayed or progressive blur suggests complications like regression, haze, ectasia, or dry eye. 1, 2

Assess for red flags: Severe pain with photophobia indicates infection; progressive irregular astigmatism suggests ectasia; and persistent blur despite clear cornea points to residual refractive error or higher-order aberrations. 1, 4

Document refraction, corneal topography, and slit-lamp findings to differentiate between refractive causes (correctable with glasses), optical causes (haze, aberrations), and structural causes (ectasia, scarring). 1