Study to Evaluate Eye Function in Patients Taking Linezolid for Six Weeks or Greater

Inclusion Criteria:

• Male and female subjects who are 18 years of age or older.

• Subjects in Treated Group:

• Subjects must have received linezolid 600 mg BID for six weeks or greater and becurrently on drug (or have received linezolid within 7 days of baseline evaluation).

• Subjects who have current signs or symptoms compatible with linezolid toxicity (i.e.optic or peripheral neuropathy) may be enrolled in the study if they are on linezolidat time of baseline evaluation (or have received linezolid within 7 days of baselineevaluation).

• Linezolid may be discontinued at any time at the primary physician's discretion andremain on the study.

• Women of childbearing potential must use adequate contraception

• Subjects in Control Group:

• Subjects will have a diagnosis similar to patients in the treated group and similarimportant co-morbidities and epidemiologic factors if possible.

Exclusion Criteria:

• Subject in Treated Group:

• Subjects with a known presence of optic or peripheral nerve damage due to anotherillness, condition or medication.

• Subjects with a pre-existing or a diagnosis at time of screening visit of anophthalmologic condition that would adversely affect the study testing protocol (e.g.dense cataracts, macular degeneration, retinitis pigmentosa).

• Subjects who are currently receiving or anticipated to receive another medication,antibiotic or other, that has known potential to produce ocular or neurologic toxicityindistinguishable from that caused by linezolid or lactic acidosis.

• Subjects with a history of significant exposure, in the opinion of the investigatorand with prior discussion with the medical monitor, to medications known to produceoptic or peripheral neuropathy.

• Subjects with an active communicable disease (i.e., tuberculosis assessed as currentlycommunicable) and subjects on active treatment for tuberculosis or other mycobacterialdisease that include drugs that have known potential to produce ocular or neurologictoxicity.

• Subjects with severe liver disease or abnormal liver function test.

• Subjects in Control Group:

• Subjects must not currently be taking linezolid or have received it for more than 7days at any time.

• Subjects with a known presence of optic or peripheral nerve damage due to anotherillness, condition or medication.

• Subjects with a pre-existing or a diagnosis at the screening visit of anophthalmologic condition that would adversely affect the study testing protocol (e.g.dense cataracts, macular degeneration, retinitis pigmentosa).

• Subjects who are currently receiving another medication, antibiotic or other, that hasknown potential to produce ocular or neurologic toxicity indistinguishable from thatcaused by linezolid or lactic acidosis.

• Subjects with a history of significant exposure, in the opinion of the investigatorand with prior discussion with the medical monitor, to medications known to produceoptic or peripheral neuropathy.

• Subjects with an active communicable disease (i.e., tuberculosis assessed as currentlycommunicable) and subjects on active treatment for tuberculosis or other mycobacterialdisease that include drugs that have known potential to produce ocular or neurologictoxicity.