Evaluation of actual vs expected photodynamic therapy spot size.
OBJECTIVE
To determine the accuracy of the photodynamic therapy (PDT) laser spot size on the retina as generated by 2 Food and Drug Administration (FDA)-approved lasers.


METHODS
Prospective observational case series.


METHODS
Fundus photographs were taken of 1 eye of each of 10 subjects with the WinStation 4000 fundus photography system (OIS; Ophthalmic Imaging Systems, Sacramento, California, USA); disc size was calculated using OIS software. Slit-lamp photographs were taken of the PDT laser spot focused on the retina adjacent to the optic disc, using various spot sizes in combination with 3 different contact lenses and 2 different lasers. Spot size at the retina was determined by measuring the ratio of disc diameter to spot diameter in Adobe Photoshop (San Jose, California, USA) and applying this ratio to the OIS disc measurements.


RESULTS
Spot size at the retina averaged 87% of expected spot size for the Coherent Opal laser (Coherent Inc, Santa Clara, California, USA) and 104% of expected spot size for the Zeiss Visulas laser (Carl Zeiss Meditec Inc, Dublin, California, USA)(P = .002). Multivariate analysis demonstrated that percentage of expected spot size decreased with larger spot diameter (P = .01 for Coherent laser; P = .02 for Zeiss laser).


CONCLUSIONS
PDT spot size at the retina appears to be consistently smaller than expected for the Coherent laser while the spot size was consistently within 10% of expected size for the Zeiss laser. The deviation from expected size increased with larger spot size using the Coherent laser.
Ranchod
Tushar M
TM
Scheie Eye Institute, Department of Ophthalmology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Brucker
Alexander J
AJ
Liu
Chengcheng
C
Cukras
Catherine A
CA
Hopkins
Tim B
TB
Ying
Gui-Shuang
GS
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D020256:Choroidal Neovascularization / Q000188:drug therapy* / Q000209:etiology; D005260:Female; D005451:Fluorescein Angiography; D006801:Humans; D054023:Lasers, Semiconductor / Q000627:therapeutic use*; D007908:Lens, Crystalline / Q000503:physiopathology; D028022:Low-Level Light Therapy; D008268:Macular Degeneration / Q000150:complications / Q000188:drug therapy*; D008297:Male; D008875:Middle Aged; D010778:Photochemotherapy; D010781:Photography; D017319:Photosensitizing Agents / Q000627:therapeutic use*; D011166:Porphyrins / Q000627:therapeutic use*; D011446:Prospective Studies; D012030:Refractive Errors / Q000175:diagnosis; D015203:Reproducibility of Results; D012160:Retina / Q000528:radiation effects; D000077362:Verteporfin
D017319:Photosensitizing Agents; D011166:Porphyrins; D000077362:Verteporfin