A number of systemic metabolic disorders of genetic origin affect the anterior portion of the eye. Many of the corneal manifestations of systemic disease are alterations in corneal clarity caused by abnormal storage of metabolic substances .
They are usually Autosomal Recessive and a single enzyme defect/absence often accounts for the clinical manifestations. Various gene loci have been determined along with its biochemical defect causing Metabolic Keratopathy(MK).
- 1 Disease Entity
- 1.1 Disease
- 1.2 Etiology
- 1.3 Risk Factors
- 1.4 General Pathology
- 1.5 Pathophysiology
Metablic keratopathies can be confused with dystrophies as they usually ocular bilaterally and are often associated with systemic involvement.
The distinguishing points can be :
- MK affects the peripheral as well as the central cornea
- The corneal changes in metabolic disorders may involve more than one layer of the cornea
- Progressses over time.
- Non- Nutritional
- Diabetes Mellitus
- Amino Acid
- Nucleic Acids
- Protein Metabolism
- Disorders of Immunoglobulin Synthesis
The manifestations are dependant upon various enzymatic defects and the accumulation of the toxic metabolic substances. These substances depending how they interact with the various tissues of the body can produce no signs, minimal signs, disabling affects (ocular, cardiac, neurological deficits) or can also also be potentially lethal.
Usually are Familial, Autosomal Recessive and are due to single enzyme defect/absence.
General PathologyEnzymatic defects along the normal path of metabolism cause accumulation of toxic by products which circulate in the body. Depending upon the level of toxicity, they might be disabling or even life threatening.
Although there are at least 8 separate syndromes, several features are common to all. Heparan sulfate, dermatan sulfate, and keratan sulfate, the GAGs normally present in highest concentration, are the accumulated metabolites.
Microscopic deposits of mucopolysaccharide are found in the keratocytes and stroma It may involve the corneal epithelium and endothelium
MPS I is divided into three subtypes based on severity of symptoms. All three types result from an absence of, or insufficient levels of, the enzyme alpha-L-iduronidase.
MPS II (Hunter's syndrome )
In contrast to MPS I, the corneal changes in MPS II rarely occur and do not usually significantly impair vision.
They usually have -
•Lack of corneal clouding
•X-linked rather than Autosomal Recessive inheritance.