Asynchronous visual recovery and transient myopic-like shift in the hyperopic eye after FS-LASIK for mixed anisometropia: a case report

Technical Summary: Asynchronous Visual Recovery and Transient Myopic-like Shift in Hyperopic Eyes After FS-LASIK for Mixed Anisometropia

Problem Statement
Femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) is a standard procedure for correcting myopia, hyperopia, and astigmatism. However, the early postoperative recovery trajectory for hyperopic corrections is known to be more variable than for myopic corrections due to differences in ablation profiles (midperipheral ablation for central steepening vs. central flattening) and subsequent epithelial remodeling. In patients with mixed anisometropia (one myopic eye and one hyperopic eye), simultaneous bilateral FS-LASIK presents a unique clinical challenge: the two eyes undergo distinct ablation patterns and healing responses simultaneously. While accommodative factors and transient refractive fluctuations are documented, the specific phenomenon of asynchronous visual recovery accompanied by a transient myopic-like shift in the hyperopic eye during the early postoperative period remains under-documented. This case report addresses the clinical presentation and management of such a scenario to prevent premature misdiagnosis of undercorrection or refractive regression.

Methodology
This is a single-case report of an 18-year-old male with mixed anisometropia (right eye: myopic astigmatism; left eye: hyperopic astigmatism).

• Preoperative Assessment: Comprehensive evaluation included manifest and cycloplegic refraction, Pentacam corneal tomography, Corvis ST biomechanical analysis, axial length measurement, and slit-lamp/fundus examinations.
• Surgical Intervention: The patient underwent uneventful bilateral FS-LASIK using the MEL 90 platform with a Triple-A ablation profile.
  • Right Eye (Myopic): 110 µm flap, 6.30 mm optical zone, 94 µm expected ablation depth.
  • Left Eye (Hyperopic): 110 µm flap, 6.50 mm optical zone, 33 µm expected ablation depth.
  • Residual stromal bed thickness was estimated at 424 µm (OD) and 484 µm (OS).
• Postoperative Monitoring: The patient was followed up at days 4, 11, 18, and 25, and at 1 and 2 months. Assessments included uncorrected distance visual acuity (UDVA), best-corrected visual acuity (BCVA), manifest refraction, and cycloplegic refraction (specifically on day 4). Pentacam tomography was performed early postoperatively to rule out ectasia or decentered ablation.
• Management Strategy: Upon observing a myopic shift and reduced vision in the left eye, the team employed conservative management: short-acting cycloplegic agents (compound tropicamide), reduction of near work, and accommodative relaxation training. No enhancement surgery was performed.

Key Results

• Asynchronous Recovery: By postoperative day 4, the right eye (myopic correction) achieved 1.0 UDVA. In contrast, the left eye (hyperopic correction) had 0.5 UDVA and a manifest refraction of −1.00 DS, suggesting a myopic shift.
• Cycloplegic Discrepancy: Crucially, cycloplegic refraction of the left eye on day 4 revealed a hyperopic state (+0.25 DS/-0.50 DC), with BCVA improving to 1.0. This indicated that the manifest myopic shift was driven by accommodative spasm rather than surgical undercorrection or regression.
• Refractive Fluctuation: Over the subsequent weeks, the left eye's manifest refraction fluctuated (reaching −1.75 DS on day 11) before gradually stabilizing.
• Final Outcome: By 1 and 2 months postoperatively, both eyes achieved 1.0 UDVA. The left eye's refraction stabilized near emmetropia (+0.00 DS/+0.25 DC). Early Pentacam scans confirmed regular corneal morphology with no signs of decentered ablation or ectasia.

Key Contributions

1. Documentation of Asymmetry: The report provides a detailed clinical example of how mixed anisometropia can lead to asynchronous visual recovery following bilateral FS-LASIK, where the hyperopic eye lags behind the myopic eye.
2. Differentiation of Refractive States: It highlights the critical importance of distinguishing between true surgical undercorrection/regression and transient, accommodation-driven myopic shifts in the early hyperopic postoperative period. The discrepancy between manifest and cycloplegic refraction served as the diagnostic pivot.
3. Conservative Management Protocol: The case demonstrates that short-term observation and conservative interventions (cycloplegia, visual hygiene) are effective for managing early myopic-like shifts in hyperopic eyes, provided corneal tomography is normal.

Significance and Claims
The authors claim that this case underscores the necessity of a holistic evaluation approach when slow visual recovery or a myopic-like shift occurs in the hyperopic eye after FS-LASIK. Specifically, they argue that:

• Premature Judgment is Risky: Clinicians should not judge undercorrection or the need for retreatment based solely on a single early manifest refraction result, especially when a clear discrepancy exists between manifest and cycloplegic refraction.
• Dynamic Recovery: The early myopic-like shift should be interpreted as part of a dynamic recovery process involving accommodative adaptation and epithelial remodeling, rather than a definitive surgical failure.
• Clinical Caution: In the absence of corneal morphological abnormalities (e.g., ectasia, decentered ablation), short-term observation and conservative management are prudent strategies to avoid unnecessary retreatment.

The paper concludes modestly, acknowledging limitations such as the short follow-up period (2 months) and the single-case nature of the study, which prevents the determination of incidence rates or the full elucidation of underlying mechanisms. However, it serves as a cautionary guide for clinicians managing mixed anisometropia to ensure accurate postoperative assessment.