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Hyaline degeneration of the cornea has been described by Smolin and Thoft1 as a specific and rare pathological entity. Other authors have used the term hyaline degeneration of the cornea synonymous with climatic droplet keratopathy, or spheroidal degeneration of the cornea.2 A literature search failed to reveal any cases of initially diagnosed hyaline degeneration of the cornea as a precursor of Salzmann’s corneal degeneration. We present the first case known to us of initially diagnosed hyaline degeneration of the cornea, assumed to be a precursor of Salzmann’s corneal degeneration.
A 34 year old woman was referred to our department in April 1998 with increasing opacity of the left cornea. Her medical and ophthalmological history was uneventful. The lower third of the left cornea showed a slightly elevated, yellowish, subepithelial opacity, sharply demarcated and separated from the limbus by a marked interspace (Fig 1A). The right eye was without pathological findings. The corneal opacity was removed by a scarifier both because of persistent foreign body sensation and for diagnostic purposes.
The histological examination of the removed corneal tissue revealed marked, diffuse hyalinosis of the stroma (Fig 1B), and focal degenerations of the overlying corneal epithelium. The presence of amyloid substance was excluded by Congo red staining. Electron microscopy demonstrated the described hyaline areas to represent collagenous tissue (Fig 1C). The assessment of the clinical and histological appearance of the corneal changes led to the diagnosis of hyaline degeneration of the cornea, according to the classification of Smolin and Thoft.1
After a period of 2 years the patient presented with recurrent corneal opacity extending beyond the initial pathological area. The clinical appearance of the opacity was markedly different, consisting of several, peripheral, subepithelial, white, slightly prominent lesions. The corresponding juxtalimbal cornea was characterised by cloudy opacification and the start of vascularisation (Fig 1D). The cornea of the right eye, which was without pathological findings 2 years earlier, now exhibited a circumscribed injection of limbal vessels as well as a punctiform, superficial opacity at a paracentral location (Fig 1E). The described findings were unchanged at the time of the most recent examination of the patient in August 2002. The clinical aspect of the left eye and the bilateral occurrence of corneal disease enabled the diagnosis of Salzmann’s corneal degeneration.
The diagnosis of Salzmann’s corneal degeneration is made clinically, with subepithelial, prominent corneal lesions representing the most important sign of this disease.3
We believe that the initial corneal alteration, clinically diagnosed as hyaline degeneration of the cornea, represents a precursor of Salzmann’s corneal degeneration. This assumption is based on the fact that the respective histological findings already indicated the presence of this pathology.4–6 In the region of nodular thickening the superficial stromal tissue consists of collagen fibrils which are hyalinised and arranged in an irregular fashion in the absence of inflammatory changes or vascularisation. The corneal epithelium shows focal degenerations, while Bowman’s membrane is not identified at its usual subepithelial location.
This case gives rise to the question as to whether hyaline degeneration may exist as a separate entity. Furthermore, if hyaline degeneration of the cornea is considered to be a precursor of Salzmann’s corneal degeneration, the apparently spontaneous development of this condition in this case does not conform to this description. The published cases of Salzmann’s corneal degeneration are almost without exception associated with a history of chronic or recurrent keratoconjunctivitis3,4,7 and, less frequently, with repeated surgical trauma8 or corneal dystrophy.8,9 The spontaneous occurrence of Salzmann’s corneal degeneration we report has only rarely been described.3,5,8 A possible explanation for this may be that two variants of Salzmann’s corneal degeneration exist: a secondary variant, associated with different corneal pathologies, and a primary one. Further work is required to determine whether the aetiology of the primary variant might be related to limbal insufficiency, which eventually causes both eyes to be affected, as is suggested by the onset of clinical signs of corneal conjunctivalisation in our patient.10