8.3 Scleral Thickening

patients with low dietary iron or chronic blood loss associated with duodenal ulcers, ulcerative colitis, and gluten enteropathy [78].

Blue sclerae occasionally has been reported associated with myasthenia gravis [83].

8.2.2.2 Paralimbal Scleromalacia

Paralimbic scleromalacia or spontaneous intercalary scleral perforation is a scleral degenerative process which appears in either one or both eyes of young individuals of either sex; it is characterized by a noninflammatory, painless scleral thinning of the corneoscleral limbus (between the ciliary body and the limbus) which leads to a small, nonprogressive, well-defined hole with iris prolapse [38, 65, 66, 74, 75, 153–155]. Sometimes, the pupil may be drawn up into the hole. A small perforating scleral vessel may run through the defect to anastomose with the posterior ciliary circulation [38]. Differential diagnosis of paralimbic scleromalacia should include scleromalacia perforans, since both conditions have loss of scleral substance, lack of inflammatory reaction, and painless development. Unlike scleromalacia perforans, paralimbic scleromalacia affects individuals between 25 and 50 years of age without evidence of rheumatoid arthritis, and it has a good prognosis without treatment (Table 4.11).

8.3Scleral Thickening

8.3.1Nanophthalmos

The characteristics of the nanophthalmic eye include a thickened sclera (up to 2 mm), small cornea, high hyperopia (up to 20 diopters), shallow anterior chamber, and a tendency for the development of uveal effusion. Nanophthalmos is usually bilateral and may be inherited following either a dominant or a recessive pattern [156, 157]. The thickening of the sclera may cause vortex vein compression which results in impaired venous drainage; this may lead to uveal effusion and serous retinal detachment [158–160]. The ultrastructure of nanophthalmic sclera has been described with conflicting results [161, 162]. Yue and coworkers found that the levels of glycosaminoglycans were markedly reduced in

cell cultures of nanophthalmic scleral cells; [159] the decreased level of glycosaminoglycans may result either from a reduced synthesis, or an increased degradation, or a combination of both. These in vitro findings conflict with the in vivo findings of Trelstad and coworkers who reported increased quantities of Alcian blue staining material that they thought to be glycosaminoglycan in the sclera of two nanophthalmic patients [160]. Whichever the case is, the abnormalities in glycosaminoglycan metabolism may lead to the abnormal collagen fiber formation and packing of collagen bundles [161], which may in turn contribute to the thickening of sclera and the formation of nanophthalmos. In a later study, Yue and coworkers found that the levels of fibronectin were increased [162].

The diagnosis of nanophthalmos is based on clinical findings. Resolution of effusions may be achieved with surgical decompression of the vortex veins [157].

8.3.2Scleropachynsis

Bilateral localized thickening of the inner two thirds of the posterior temporal sclera has been reported in one case as the cause of choroidal compression and maculopathy [44]. Ultrastructurally, the collagen fibers in the inner two thirds of the sclera in the submacular region were enlarged in diameter; mucopolysaccharide deposition was detected between the bundles of collagen.

8.3.3Phthisis Bulbi

The term phthisis bulbi is applied to those eyes which show not only diffuse degeneration or atrophy, but also shrinkage and disorganization of the ocular contents after severe injury or inflammation. The sclera becomes markedly thickened and irregular due to scarring. The intraocular structures also are replaced by scarred tissue. It is not known whether internal fibrosis leads to the loss of intraocular pressure or the lack of ocular tension results in intraocular scarring.