Penetrating excimer Laser-assisted keratoplasty for corneal epithelial downgrowth in childhood

A 5-year-old boy was presented in our department one month after corneal injury caused by metal stick, complaining of pain in his right eye and pronounced photosensitivity. The primary removal of corneal foreign body took place in an external clinic. BCVA was 0.6 OD and 1.0 OS. The slit-lamp biomicroscopy examination revealed a corneal intrastromal whitish membranous structure in the right eye spreading over the visual axis (Figure 1).

examination of the excised cornea showed downgrowth of stratified squamous epithelium through the Bowman's layer into the corneal stroma ( Figure 3).
One-year after the intervention, the patient complained about impaired vision. Despite the treatment and keratoplasty the BCVA was 0.25 OD. The graft showed focal nonvascularized pannus adjacent to the double running sutures (Figure 4).
A corneal suture removal combined with superficial lamellar keratectomy had been performed. At 20 months of follow-up, after intensive local anti-inflammatory therapy, the BCVA improved up to 1.0 OD. The graft remained clear and showed no evidence of recurrence of epithelial downgrowth ( Figure 5).

Discussion
Epithelial downgrowth (also termed epithelial ingrowth) is a vision-threatening complication, where epithelial cells invade into intraocular structures. It is a rare complication of ophthalmic surgery or penetrating ocular trauma [1].
There are several important factors for physiological corneal epithelial wound healing process, including the type and depth of the injury, presence of inflammation, systemic disease, medication, neurotrophic keratopathy or potency of limbal stem cells.
Epithelial downgrowth is formed in a cystic, diffuse (sheets) or combined pattern. Proliferating cells that form an inclusion cyst connected to the wound occurs in cystic pattern, tends to have better prognosis [1]. In case of diffuse form, the epithelium can invade through the cornea to iris, trabecular meshwork and ciliary body and in extreme cases into the retina and under the choroid resulting in tractional retinal detachment. Furthermore, it can cause multiple other severe complications including secondary angle closure glaucoma, corneal decompensation, lens dislocation, astigmatism and visual impairment or blindness. Additionally, in our case corneal melting was one of the possible vision-threatening complications.
Several clinical features could be found in case of epithelial downgrowth. These include anterior chamber cells or iritis, glaucoma (unresponsive to conventional therapy), posterior corneal and iris membrane [2]. If the diagnosis of epithelial downgrowth is questionable the optical coherence tomography of the anterior segment, confocal microscopy or ultrasound biomicroscopy (UBM) can be performed [3][4][5][6][7].
Cytokeratin as immunohistochemical marker is essential to confirm epithelial downgrowth [8].
In any early intervention (lamellar or penetrating keratoplasty) it is essential to preserve the limbus area to provide the best visual outcome.
The downgrowth of surface epithelium is a disastrous but fortunately rare complication of intraocular surgery [2] or injury [1,4,6,7,[9][10][11]. In the literature we can find several cases of epithelial downgrowth after trauma, which can lead years after the primary injury to loss of vision [1,4,9,10,12]. For this reason, an early and invasive intervention to achieve better visual outcome is required [4,6,7,9].
In this case, one of the possible therapies of choice is deep anterior lamellar keratoplasty (DALK). This technique had been proved to be an efficient alternative to penetrating keratoplasty in several indications. Nevertheless, performing of DALK could be very challenging, especially when there is significant scaring of deep corneal stroma. Many surgeons may use penetrating keratoplasty as the primary procedure [13]. Among other possible complication, that we have to take into consideration, belong ruptures and microperforations of Descemet's membrane, as well as interface haze and irregularities [13] using DALK.
In our case, where we cannot surely exclude epithelial ingrowth in deep stroma or even in endothelium and Descemet's membrane, DALK would not be the therapy of choice.
With children as patients we have to consider not only longterm complications of epithelial downgrowth but also a complication caused by any intervention. Regarding to patient's age and future eye-development was in our case the therapy of choice penetrating keratoplasty with excimer laser [14].

Conclusion
In summary, we showed a case of child which presented only few months after corneal injury with severe complication (pain, photosensitivity, vision-impairment) as well as clinical features associated with epithelial downgrowth. To the best of our knowledge, we report for the first time of a case of epithelial downgrowth after corneal injury treated with excimer laser keratoplasty with promising outcome in childhood. Future follow-up and regular check-ups of our young patient are still necessary to confirm long-term results.