The LASH Contact Lens Study is a prospective longitudinal study of silicone hydrogel (SH) contact lens wearers who sleep in their lenses for up to 29 consecutive nights (30 days) of continuous wear (CW), with monthly disposal. Up to 207 healthy nearsighted or farsighted patients with minimal or no astigmatism and no contraindications to CW lens use will be followed for 1 year. The primary outcome measure is the time to development of a corneal inflammatory event (CIE) as defined by slit lamp findings and patient symptoms. The main exposure of interest is corneal staining. Other key exploratory variables include bacterial contamination of study lenses and inflammatory mediators found in the tear film.

Inclusion Criteria:

1. The patient must be at least 15 years old. Children younger than this may not be mature enough for CW, and may have difficulty following the strict instructions required for CW or sitting through the exam procedures.
2. The patient must have clear central corneas and free of any anterior segment disorders.
3. The patient must have a spectacle corrected spherical refractive error between +5.50 D and -11.00 D with less than or equal to 1.00 D refractive cylinder. The parameters of the Ciba Vision Night and Day Lenses range from +6.00 to -10.00 D, and can correct the refractive range of this population. Monovision correction will be allowed only if the near eye does not exceed +6.00 D.
4. The patient must be correctable to 20/25 or better with spectacles. Amblyopia will be excluded.
5. Flat and steep corneal curvatures from SimK readings must be between 39.00 and 48.00 D. Corneal curvatures outside this range may be indicative of a disease state, and patients are not expected to comfortably wear either the 8.4 mm or 8.6 mm base curve available in Night and Day.(Dumbleton K 2002)
6. Can be successfully fit with lotrafilcon A lenses at the enrollment visit.

Exclusion Criteria:

1. The patient has worn rigid gas permeable lenses within the last 30 days or PMMA lenses within the last 3 months. These lenses can transiently alter the corneal shape and influence the fitting of soft lenses.
2. The patient must not be a current extended wear user of lotrafilcon A lenses.
3. The patient has an autoimmune disease (except for Hashimoto's Thyroiditis), immunocompromising disease, connective tissue disease, atopic dermatitis, insulin dependent diabetes, or any other systemic disease that in the investigator's opinion will affect ocular health.
4. The patient is taking chronic systemic medications such as corticosteroids, antimetabolites, or non-steroidal anti-inflammatory agents or any other medication that in the investigator's opinion will affect ocular physiology.
5. The patient has any ocular disease or condition such as aphakia, corneal dystrophies, corneal edema, external ocular infection, iritis, or had any anterior segment surgery.
6. The patient is taking any ocular medications.
7. The patient must have less than or equal to grade 2 on any of the slit lamp observations of: upper tarsal papilla, corneal staining, corneal neovascularization, conjunctival injection, and lid erythema or scales. Slit lamp findings higher than grade 2 bias the patient toward an adverse event and it may be difficult to detect true change related to CW.
8. The patient is pregnant.

study volunteers from academic community willing to wear extended wear contact lenses