The purpose of this research study is to find out if the new Brillouin Ocular Scanner can measure the variation (difference) of the corneal elastic changes involved in the onset of corneal ectasia, induced by LASIK surgery and cornea collagen crosslinking (CXL) treatment. Ectasia refers to the thinning and bulging of the cornea and results in severe vision degradation (loss), which may occur because of a progressive disease (keratoconus) or because of LASIK surgery. It is believed that the structural weakening of the cornea plays a major role in developing ectasia. CXL is a treatment that is able to halt the progression of ectasia.

The Brillouin Ocular Scanner is a technique based on the principles used in the laser speed measuring of a car (radar gun). When laser light illuminates a moving sample, a portion of the light slightly changes color. In our body, e.g in eye and corneal tissue, very weak sound waves are naturally present and they can induce a similar color shift. Measuring this color shift with a sensitive light color meter (spectrometer), we will measure the sound speed in the tissue.

Inclusion Criteria:

• Subjects with healthy cornea
• Patients with mild, moderate, or advanced keratoconus
• Subjects diagnosed with PMD
• Patients before and after LASK surgery
• Patients with keratoconus before and after collagen crosslinking treatment

Exclusion Criteria:

• Normal volunteer group: presbyopia and/or cataract
• Keratoconus subjects group: corneas with scars developed, received any ocular surgery, such as laser vision correction surgeries or CXL treatment
• Subjects diagnosed with PMD: excludes corneas received any ocular surgery, such as laser vision correction or CXL treatment
• Patients before and after LASK surgery Corneas received priori ocular surgeries, taking any ocular medications except season allergy medicine such as artificial tears