Advertisement

Transient corneal edema circumscribed to the LASIK flap after uneventful cataract surgery

      Previous studies have shown how LASIK surgery induces long-term changes in the corneal flap,
      • Vesaluoma M.
      • Perez-Santonja J.
      • Petroll W.M.
      • Linna T.
      • Alio J.
      • Tervo T.
      Corneal stromal changes induced by myopic LASIK.
      the LASIK interface,
      • Dawson D.G.
      • Edelhauser H.F.
      • Grossniklaus H.E.
      Long-term histopathologic findings in human corneal wounds after refractive surgical procedures.
      and the residual stromal bed.
      • Cañadas P.
      • de Benito-Llopis L.
      • Hernández-Verdejo J.L.
      • Teus M.A.
      Comparison of keratocyte density after femtosecond laser vs mechanical microkeratome from 3 months up to 5 years after LASIK.
      Dawson et al.
      • Dawson D.G.
      • Schmack I.
      • Holley G.P.
      • Waring 3rd, G.O.
      • Grossniklaus H.E.
      • Edelhauser H.F.
      Interface fluid syndrome in human eye bank corneas after LASIK: causes and pathogenesis.
      have reported different hydraulic behaviours between stromal bed and LASIK flap in human eye bank corneas, in 2 experimental models of interface fluid syndrome.
      We present a case of transient corneal edema after cataract surgery, confined to the LASIK flap. This would confirm, in vivo, the different hydraulic behaviour of the LASIK flap compared with the stromal bed and the rest of the cornea.
      A 58-year-old male was referred to our clinic for cataract surgery in his left eye. Seven years before he had had an uneventful femtosecond LASIK surgery to correct a refractive error of –4.00, –0.75 × 90° in his left eye with plano result. He had a nuclear cataract, 2530 endothelial cells/mm2, and the central corneal thickness was 520 μm measured by ultrasonic pachymeter. He had neither signs nor family history of glaucoma. An uneventful phacoemulsification technique was performed, and a monofocal intraocular lens was implanted. The patient was instructed to apply topical antibiotic and steroid drops every 6 hours.
      On postoperative day 1, the uncorrected distance visual acuity was 20/80. The slit-lamp examination showed corneal edema circumscribed to the LASIK flap (Fig. 1); the underlying residual stromal bed and cornea surrounding the flap limits were clear. The intraocular pressure (IOP) was 25 mm Hg and the lens was correctly positioned in the capsular bag. No fluid was detected in the interface between the flap and the stromal bed with the anterior segment optical coherence tomography (Fig. 2). Topical timolol maleate twice a day and hyperosmotic eye drops 3 times daily were prescribed in addition. One week later, the UCVA improved to 20/25, the flap edema was completely resolved, and IOP was 16 mm Hg.
      Figure thumbnail gr1
      Fig. 1Slit-lamp photography of anterior segment.
      Figure thumbnail gr2
      Fig. 2Anterior segment optical coherence tomography of patient’s cornea.
      Corneal hydration is determined by factors such as endothelial pump, epithelial barrier, water evaporation, IOP, and stromal swelling pressure, mainly because of keratan and chondroitin sulfate.
      • Nishida T.
      • Saika S.
      Cornea and sclera: anatomy and physiology.
      It seems that the anatomical and biomechanical changes that occur in the cornea after a LASIK flap creation might alter the balance between the factors that define the corneal hydration or the response to an acute hydraulic stress. In fact, Dawson et al.
      • Dawson D.G.
      • Schmack I.
      • Holley G.P.
      • Waring 3rd, G.O.
      • Grossniklaus H.E.
      • Edelhauser H.F.
      Interface fluid syndrome in human eye bank corneas after LASIK: causes and pathogenesis.
      evaluated the behaviour of human eye-bank donor corneas that had undergone LASIK surgery years before, using 2 models that caused cornea edema. The authors found that the fluid tends to accumulate within the flap and in the flap–stroma interface, thus proving that the flap has different properties, from the hydraulic conductivity point of view, than the rest of the cornea.
      Interestingly, in our case, no fluid was found in the interface, but a corneal edema confined to the LASIK flap developed, suggesting a different hydraulic behaviour of the flap compared with the stromal bed “in vivo.”
      It is accepted that the flap creation changes the corneal biomechanical properties. Therefore, the superficial corneal lamellae of the LASIK flap may be less strongly attached to the peripheral cornea than the posterior lamellae within the stromal bed,
      • Teus M.A.
      • de Benito-llopis L.
      Laser-assisted subepithelial keratectomy with MMC to treat post-LASIK myopic regression.
      and this fact may explain the different behaviour of these areas to the sudden increase in IOP.
      Furthermore, LASIK induces a reorganization of the stromal keratocyte density. Cañadas et al.
      • Cañadas P.
      • de Benito-Llopis L.
      • Hernández-Verdejo J.L.
      • Teus M.A.
      Comparison of keratocyte density after femtosecond laser vs mechanical microkeratome from 3 months up to 5 years after LASIK.
      found a significant decrease of the keratocyte density in both the stromal flap and the stromal bed months after LASIK, although the average cell density throughout the whole cornea was not decreased. Keratocytes are involved in the synthesis of collagen molecules and glycosaminoglycans, both crucial in maintaining stromal homeostasis. In fact, the specific distribution of the different proteoglycans, which have different water affinity, may play a role in the establishment of water gradients across the cornea (i.e., keratan sulfate, more hydrophilic, is predominantly located in the posterior stroma, whereas dermatan sulfate, less hydrophilic, is predominantly located in the anterior stroma).
      • Vesaluoma M.
      • Perez-Santonja J.
      • Petroll W.M.
      • Linna T.
      • Alio J.
      • Tervo T.
      Corneal stromal changes induced by myopic LASIK.
      • Castoro J.A.
      • Bettelheim A.A.
      • Bettelheim F.A.
      Water gradients across bovine cornea.
      Therefore, LASIK-induced changes in the keratocyte density might modify the normal distribution of proteoglycans throughout the cornea, thus explaining the peculiar distribution of water seen in acute corneal edema in these eyes.
      Finally, the stronger adhesion that a femtosecond laser-created flap seems to have to the stromal bed in comparison with mechanical microkeratome flaps
      • Kim J.Y.
      • Kim M.J.
      • Kim T.I.
      • Choi H.J.
      • Pak J.H.
      • Tchah H.
      A femtosecond laser creates a stronger flap than a mechanical microkeratome.
      could explain why in our case no interface fluid syndrome was found.
      In conclusion, both the anatomical changes and the corneal ultrastructural and biochemical reorganization that occur after LASIK surgery in the cornea
      • Dupps Jr, W.J.
      • Wilson S.E.
      Biomechanics and wound healing in the cornea.
      may modify the response of the flap to an acute hydraulic stress. An increased IOP or a transient endothelial dysfunction that commonly happen after cataract surgery might have caused the corneal edema confined to the LASIK flap in our case.

      References

        • Vesaluoma M.
        • Perez-Santonja J.
        • Petroll W.M.
        • Linna T.
        • Alio J.
        • Tervo T.
        Corneal stromal changes induced by myopic LASIK.
        Invest Ophthalmol Vis Sci. 2000; 41: 369-376
        • Dawson D.G.
        • Edelhauser H.F.
        • Grossniklaus H.E.
        Long-term histopathologic findings in human corneal wounds after refractive surgical procedures.
        Am J Ophthalmol. 2005; 139: 168-178
        • Cañadas P.
        • de Benito-Llopis L.
        • Hernández-Verdejo J.L.
        • Teus M.A.
        Comparison of keratocyte density after femtosecond laser vs mechanical microkeratome from 3 months up to 5 years after LASIK.
        Graefes Arch Clin Exp Ophthalmol. 2013; 251: 2171-2179
        • Dawson D.G.
        • Schmack I.
        • Holley G.P.
        • Waring 3rd, G.O.
        • Grossniklaus H.E.
        • Edelhauser H.F.
        Interface fluid syndrome in human eye bank corneas after LASIK: causes and pathogenesis.
        Ophthalmology. 2007; 114: 1848-1859
        • Nishida T.
        • Saika S.
        Cornea and sclera: anatomy and physiology.
        in: Krachmer J.H. Mannis M.J. Holland E.J. Cornea. 3rd ed. Mosby, Elsevier, St. Louis, Mo.2011: 3-25
        • Teus M.A.
        • de Benito-llopis L.
        Laser-assisted subepithelial keratectomy with MMC to treat post-LASIK myopic regression.
        J Cataract Refract Surg. 2007; 33: 1674-1675
        • Castoro J.A.
        • Bettelheim A.A.
        • Bettelheim F.A.
        Water gradients across bovine cornea.
        Invest Ophthalmol Vis Sci. 1988; 29: 963-968
        • Kim J.Y.
        • Kim M.J.
        • Kim T.I.
        • Choi H.J.
        • Pak J.H.
        • Tchah H.
        A femtosecond laser creates a stronger flap than a mechanical microkeratome.
        Invest Ophthalmol Vis Sci. 2006; 47: 599-604
        • Dupps Jr, W.J.
        • Wilson S.E.
        Biomechanics and wound healing in the cornea.
        Exp Eye Res. 2006; 83: 709-720