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Measurement of corneal thickness with ultrasound
Assessment of corneal thickness prior to refractive surgery or crosslinking. Corneal thickness plays also a role in the interpretation of the measured intraocular pressure in glaucoma assessed with applanation tonometry.
Ultrasonic pachymetry is based upon the differential return of the ultrasonic waves by varying tissue types in the eye. Sound waves are emitted by a piezoelectric crystal and delivered with a probe. For axial measurements the probe is placed perpendicular to the corneoscleral surface. Ultrasonic pachymetry can either be performed with the contact method when direct contact between the corneal surface and probe is made or with immersion biometry applying an eyecup between the eyelids filled with immersion fluid (e.g. balanced salt solution, methycellulose).
Indication: keratorefractive surgery, glaucoma