title: Very high-frequency ultrasound analysis of non-contact holmium laser thermal keratoplasty treatment spots.
abstract: OBJECTIVE
  To objectively measure the corneal treatment spots in vivo using very high-frequency ultrasound (VHFU) after non-contact laser thermal keratoplasty (LTK) to better understand the variability and regression of refractive outcomes.
  
  
  METHODS
  In an institutional setting, VHFU was performed on 128 spots (8 eyes of 4 patients) using an immersion scanning technique 1 to 2 years after LTK with a single element focused transducer (50 MHz arc scanning ultrasound). Biometric techniques were used to evaluate the treatment spot depth, corresponding corneal thickness, and spot profile between patients, eyes (left/right), and by location on the cornea. The identical technique was used in a rabbit immediately after LTK to compare ultrasound versus histologic findings.
  
  
  RESULTS
  The mean treatment spot penetration depth ranged between 0.373 and 0.533 mm, representing 64% to 78% of the corneal thickness compared to previous reports of 80% to 90%. Treatment spot depth, the corresponding corneal thickness, and percentage of overall cornea penetrated differed significantly across patients. Treatment spot depth was not significantly related to the level of applied laser energy (230 to 258 mJ) (0.082 Pearson sign). Spot profiles were not uniformly cone-shaped; W- and wedge-shaped were also identified. Ultrasound findings in the rabbit were similar to histology results and confirmed evidence of epithelial remodeling.
  
  
  CONCLUSIONS
  Very high-frequency ultrasound of 128 treatment spots after non-contact LTK demonstrates epithelial remodeling and inconsistencies in penetration depth and profile.
authors.affiliation: Department of Ophthalmology, New York Hospital Presbyterian Hospital, Weill Medical College of Cornell University, 121 E 61st St, New York, NY 10021, USA. gjs2002@med.cornell.edu
authors.forename: Sandra C
authors.initials: SC
authors.lastname: Belmont
authors.forename: Sophia
authors.initials: S
authors.lastname: Chen
authors.forename: Ramon
authors.initials: R
authors.lastname: Ruffy
authors.forename: Samantha J
authors.initials: SJ
authors.lastname: Chai
authors.forename: Ronald
authors.initials: R
authors.lastname: Silverman
authors.forename: D Jackson
authors.initials: DJ
authors.lastname: Coleman
mesh_terms: D000818:Animals; D003315:Cornea / Q000000981:diagnostic imaging* / Q000601:surgery; D004195:Disease Models, Animal; D005500:Follow-Up Studies; D006801:Humans; D015948:Keratoplasty, Penetrating / Q000379:methods*; D017075:Laser Coagulation; D008875:Middle Aged; D011817:Rabbits; D012030:Refractive Errors / Q000000981:diagnostic imaging; D054140:Refractive Surgical Procedures; D012189:Retrospective Studies; D013997:Time Factors; D016896:Treatment Outcome; D014463:Ultrasonography