Siderosis Bulbi is a degenerative and pigmentary change in the eye that follows intra- ocular retention of a foreign body containing iron. Its degree of severity and rate of development depend upon the content and location of iron. Large, more posteriorly situated, and ferrous intra-ocular foreign bodies have the worst prognosis. Histopathologically, siderosis shows accumulation of iron within metabolically active cells. Cells of corneal epithelium, pupillary constrictor muscle, lens epithelium, trabecular meshwork, pars plana and retinal pigment epithelium all may be affected.
Von Hippel (1894) distinguished two types of siderosis: haematogenous in which iron is derived from the blood, and exogenous in which it is derived from an intra-ocular foreign body (IOFB).
Siderosis may lead to decreased visual acuity, iris heterochromia, brown- coloured deposits beneath anterior lens capsule and cataract formation.
Visual prognosis for siderosis is fairly good in some cases, but it is preferable to remove intraocular iron containing foreign body, wherever possible.
Hippel, Von E. Ibid., 40, pt.1, 1894. P 123.
Symptoms of Siderosis may include:
Retained intraocular foreign body are common in open globe injuries, causing multitude of adverse problems, many of them leading to severe visual disability.
Iron can ionise and diffuse throughout the eye, and then is deposited mainly as ferritin, and sometimes as cytoplasmic siderosomes, in many ocular structures.
The iron ionises and spread to all ocular tissues. It is mainly concentrated in epithelial cells (cornea, iris, ciliary body, lens and retinal pigment epithelium), iris dilator and sphincter muscle, trabecular meshwork, and neural retina.
Toxicity to essential enzyme processes due to excess of intracellular free iron leads to trabecular meshwork scarring, secondary chronic open angle glaucoma, anterior sub capsular cataract (siderosis lentis), and neural retinal degeneration.
Diagnosis depends upon clinical history and examination.
Clinically, the process of siderosis bulbi may be divided into three stages:
Structures such as iris, lens and retina can appear rusty clinically and macroscopically.
The iris is stained dark so that heterochromia results (darker colour in eye with siderosis). It is due to reddish brown staining of the iris.
Iron in anterior chamber angle may be seen as scattered black blotches which may resemble malignant melanoma. Trabecular damage due to deposits may produce glaucoma.
The lens is frequently yellow- brown with clumping of rusty material in anterior sub-capsular area. Iron deposits are radially distributed on the anterior lens capsule.
There may be pigmentary retinopathy followed by atrophy of the retina and retinal pigment epithelium. These changes may lead to profound visual loss.
Thus, clinical signs of siderosis include reduced visual acuity, mydriasis, heterochromia, brown deposits beneath the anterior lens capsule and formation of cataract. Electrophysiological changes include abnormal electroretinogram (ERG) and dark- adaptation study.
Intraocular haemorrhage may produce similar clinical and histopathological changes as are seen in retained iron IOFB. Iron deposition in tissues from an intraocular haemorrhage is known as haemosiderosis bulbi. Long standing cases may show trabecular meshwork degeneration and scarring.
Histopathologically, siderosis is characterised by accumulation of iron within metabolically active cells. Cells of corneal epithelium, pupillary constrictor muscle, lens epithelium, trabecular meshwork, pars plana and retinal pigment epithelium all may be affected.
Management entails removal of retained IOFB. Removal of IOFB may stop the progression of siderosis.
Early surgical removal of metallic IOFB is recommended for good visual prognosis. It may be done through limbal incision or by using intraocular forceps with a pars plana vitrectomy.
The cataract should be operated upon in cases developing this.
The visual prognosis for siderosis is fairly good in some cases. However, removal of intraocular iron is advocated, wherever possible. If extraction is deferred for some reason, then serial ERGs are helpful for monitoring retinal degeneration. IOFB extraction should be done if ERG deterioration is noted.
Complications may be
Prevention may minimise sight- threatening effect of siderosis.
Awareness regarding protection against ocular injuries related to dangerous work should be stressed.
Appropriate measures for protection of eyes should be encouraged.