title: Temperature-controlled retinal photocoagulation--a step toward automated laser treatment.
abstract: OBJECTIVE
  Retinal laser photocoagulation carries the risk of overtreatment due to effect variation of identically applied lesions. The degree of coagulation depends on the induced temperature increase and on exposure time. We introduce temperature controlled photocoagulation (TCP), which uses optoacoustics to determine individually exposure times necessary to create reproducible lesions.
  
  
  METHODS
  Optoacoustic temperature measurement relies on pressure waves that are excited in the retinal tissue by repetitive low-energy laser pulses. Signal amplitudes correlate with tissue temperature and are detected by a transducer in the laser contact lens. We used a continuous wave (CW) photocoagulator for treatment irradiation and superimposed probe laser pulses for simultaneous temperature measurement. Optoacoustic data of 1500 lesions (rabbit) were evaluated to develop an algorithm that controls exposure times automatically in TCP. Lesion diameters of 156 TCP lesions were compared to 156 non-controlled lesions. Histology was performed after 1 hour, and 1 and 4 weeks.
  
  
  RESULTS
  TCP resulted in exposure times from 4 to 800 ms depending on laser power chosen. Ophthalmoscopic and histologic lesion diameters were independent of power between 14 and 200 mW. TCP lesions barely were visible with a mean diameter equal to the treatment beam (130 μm). In contrast, standard lesion diameters increased linearly and statistically significantly with power. Histology confirmed sparing of the ganglion and nerve fiber layers in TCP.
  
  
  CONCLUSIONS
  TCP facilitates uniform retinal lesions over a wide power range. In a clinical setting, it should generate soft and reproducible lesions independently of local tissue variation and improve safety, particularly at short exposure times.
authors.affiliation: Department of Ophthalmology, University of Kiel, Kiel, Germany. koinzer@auge.uni-kiel.de
authors.forename: Stefan
authors.initials: S
authors.lastname: Koinzer
authors.forename: Kerstin
authors.initials: K
authors.lastname: Schlott
authors.forename: Lars
authors.initials: L
authors.lastname: Ptaszynski
authors.forename: Marco
authors.initials: M
authors.lastname: Bever
authors.forename: Susanne
authors.initials: S
authors.lastname: Kleemann
authors.forename: Mark
authors.initials: M
authors.lastname: Saeger
authors.forename: Alexander
authors.initials: A
authors.lastname: Baade
authors.forename: Amke
authors.initials: A
authors.lastname: Caliebe
authors.forename: Yoko
authors.initials: Y
authors.lastname: Miura
authors.forename: Reginald
authors.initials: R
authors.lastname: Birngruber
authors.forename: Ralf
authors.initials: R
authors.lastname: Brinkmann
authors.forename: Johann
authors.initials: J
authors.lastname: Roider
mesh_terms: D000818:Animals; D001331:Automation / Q000379:methods*; D017075:Laser Coagulation / Q000379:methods*; D009887:Ophthalmoscopy; D011817:Rabbits; D012160:Retina / Q000473:pathology* / Q000601:surgery; D012164:Retinal Diseases / Q000473:pathology / Q000601:surgery*; D013696:Temperature