A new classification of ocular surface burns.

Ocular burns constitute true ocular emergencies and both thermal and chemical burns represent potentially blinding ocular injuries. Thermal burns result from accidents associated with firework explosions, steam, boiling water, or molten metal (commonly aluminium). Chemical burns may be caused by either alkaline or acidic agents. Common alkaline agents include ammonium hydroxide used in fertiliser production, sodium hydroxide (caustic soda) used for cleaning drains and pipes, and calcium hydroxide found in lime plaster and cement. Alkaline agents are particularly damaging as they have both hydrophilic and lipophilic properties, which allow them to rapidly penetrate cell membranes and enter the anterior chamber. Alkali damage results from interaction of the hydroxyl ions causing saponification of cell membranes and cell death along with disruption of the extracellular matrix. Common acidic agents causing injury include sulphuric acid found in car batteries, sulphurous acid found in some bleaches, and hydrochloric acid used in swimming pools. Acids tend to cause less damage than alkalis as many corneal proteins bind acid and act as a chemical buVer. In addition, coagulated tissue acts as a barrier to further penetration of acid. Acid binds to collagen and causes fibril shrinkage. Historically, it has been recognised that the extent of tissue damage is a prognostic indicator of recovery following ocular surface injury. Recovery of ocular surface burns depends upon the causative agent and the extent of damage to corneal, limbal, and conjunctival tissues at the time of injury. Damage to intraocular structures influences the final visual outcome. Ballen first suggested a classification which was later modified by Roper-Hall to provide prognostic guidelines based on the corneal appearance and the extent of limbal ischaemia. This classification has become the commonly used benchmark since its introduction in 1965 (Table 1). However, in the years following the introduction of the Roper-Hall classification, our knowledge and understanding of ocular surface healing and our approach to surgical management of ocular surface burns has changed dramatically. The understanding and clinical application of the concept of limbal stem cells of the corneal epithelium and forniceal stem cells of the conjunctival epithelium, 11 has significantly improved the outcome of treatment in patients with ocular surface burns. Corneal epithelium is derived from limbal based epithelial stem cells; these slow cycling cells are believed to be located in the basal epithelial layer of the palisades of Vogt, at the limbus. 13 They are poorly diVerentiated and are thought to maintain their “stemness” through a combination of inherent cellular characteristics and the presence of a favourable microenvironment at the limbus. These stem cells provide a steady supply of daughter cells (transient amplifying cells) which maintain a constant epithelial cell mass during normal epithelial cell turnover and during epithelial wound healing. Corneal epithelial regeneration occurs in both a centripetal and circumferential manner with cells growing from the limbus towards the central cornea and also migrating along the limbus. 14 The stem cells of the conjunctiva are located in the forniceal region and migrate in a centripetal fashion away from the fornices to cover bulbar and tarsal conjunctiva. 11 New developments in the management of ocular surface burns, such as autolimbal 16 or allolimbal transplantation with or without amniotic membrane transplantation, combined with systemic immunosuppression and topical instillation of autologous serum, have all evolved from the better understanding of ocular surface regeneration and healing from limbal and forniceal stem cells. Ocular surface reconstruction procedures are being carried out with increasing frequency worldwide. However, the successes and failures reported for these procedures vary from centre to centre even for the same grade of burns. This diVerence is largely a reflection on the inadequacy of the present classification system, rather than on the use of amniotic membrane or limbal transplantation. This is particularly true for grade IV burns. In the Roper-Hall classification grade IV implies between 50%–100% limbal ischaemia and is equated with a poor prognosis. However, with present management strategies, an eye with 50% or even 75% limbal ischaemia can expect a good to fair outcome, whereas an eye with 100% ischaemia is very likely to have a poor outcome. The extent of associated conjunctival epithelial involvement is another variable of considerable prognostic significance. In eyes with total loss of limbal (and corneal) epithelium, the presence of any surviving conjunctival epithelium, is a favourable prognostic indicator when compared with eyes with total loss of corneal, limbal, and conjunctival epithelium. Conjunctival epithelial cover to the cornea (and ocular surface) is better than no epithelial cover. Conjunctivalisation of the cornea protects against progressive melting and perforation. The ensuing vascularisation promotes healing and facilitates repair. This allows the eye to settle and provides an opportunity to carry out restorative procedures at a future date. In eyes with 100% limbal and conjunctival involvement, a very poor outcome would be expected even with maximum intervention. There are several examples of good outcomes in RoperHall grade IV burns following using modern management approaches described above. Morgan and Murray treated six cases of grade IV burns with autolimbal transplantation and reported success in five eyes. Kenyon and Tseng reported use of autolimbal transplantation in 22 cases of Table 1 Classification of severity of ocular surface burns by Roper-Hall