94 CHAPTER 7 Cornea
Pseudo-Hurler dystrophy (ML III)
ML III is often considered a less severe form of ML II. The same N-acetyl-glucosaminyl- phosphotransferase enzyme is deficient, but may have more residual activity. Patients will show joint stiffness, short stature, and gingival hyperplasia.64 Though almost all patients with ML-III will eventually show corneal clouding, it may not be present at birth.68
ML IV
ML IV is a condition classically seen in the Ashkenazi Jewish population. The exact enzymatic defect for ML IV is still uncertain. This disease is primarily one with ocular findings including corneal opacities, retinal degeneration, optic neuropathy, ocular misalignment, and psychomotor retardation.69 Patients with ML IV may also have decreased proton secretion in parietal cells leading to iron deficiency anemia and achlorhydria.70
The treatment options for the MLs are limited. The corneal changes seen in ML IV are known to cause significant ocular pain and tearing as well as reduced vision.71 The pathology in the cornea with ML IV seems to be primarily limited to the corneal epithelium. Transplantation of limbal tissue and conjunctiva has been reported to help improve the corneal epithelial abnormalities from which these patients suffer.72
Miscellaneous metabolic diseases
Fabry’s disease
ETIOLOGY
Fabry’s disease is an X-linked recessive disorder resulting from a deficiency in the α-galactosidase enzyme.73 The accumulation of glycolipid leads to the observed systemic and ocular findings.
CLINICAL PRESENTATION
Ocular findings in Fabry’s disease include cataract formation, retinal vascular tortuosity, and swirls seen in the corneal epithelium called verticillata. The corneal changes are the most commonly seen ophthalmic finding and may be seen by 6 months of age.74 Systemic findings include angiokeratomas, cardiac conduction defects, mitral valve prolapse, renal dysfunction, and painful peripheral neuropathy.75
MANAGEMENT/TREATMENT AND PROGNOSIS
Treatment of Fabry’s disease currently focuses on supportive treatment for painful episodes or end-organ failure and enzyme replacement therapy. Early treatment with enzyme replacement has shown promise with reduced end-organ damage and reduced pain.75
Cystinosis
ETIOLOGY
Cystinosis is caused by a deficiency of a mem- brane-bound transport protein allowing transport of cystine out of lysosomes. The accumulation of cystine in the lysosome allows crystals to form and deposit in several different organs including the kidneys, bone marrow, pancreas, muscle, brain, and eye.76 Cystinosis is a rare AR disorder that can be divided into nonnephropathic (mild) and nephropathic (severe) forms. Nephropathic cystinosis further divides into infantile and intermediate types.77 Infantile nephropathic cystinosis is the form that has early corneal findings. Needle-like crystals first form in the peripheral cornea and over time migrate centrally.78 The deposits in the cornea may not reduce vision but will cause light sensitivity and pain.