Transpupillary thermotherapy threshold parameters: funduscopic, angiographic, and histologic findings in pigmented and nonpigmented rabbits.
OBJECTIVE
To evaluate the effect of pigmentation on threshold fluence levels, needed to produce visible and angiographic lesions, of transpupillary thermotherapy (TTT) in rabbits.


METHODS
Six pigmented and nine nonpigmented rabbits underwent TTT with an 810-nm diode laser coupled to a slit-lamp biomicroscope using a spot size of 2 or 3 mm. The power ranged from 80 to 200 mW with 1 to 3 minutes of laser exposure for pigmented rabbits and 750 to 1800 mW with 1 minute of exposure for albino rabbits. These parameters were also evaluated after compression of the globe using the contact lens to induce blanching of the optic nerve head. After the experiment, the eyes were enucleated under deep anesthesia, and the animals were killed immediately.


RESULTS
In pigmented rabbits, the threshold fluence with the 2-mm spot size was 229 J/cm2 without compression and 153 J/cm2 with compression. With the 3-mm spot size, the threshold decreased from 200 to 150 mW as the duration of exposure lengthened (2 or 3 minutes), increasing the fluence from 170 to 382 J/cm2. In nonpigmented rabbits, the threshold fluence with the 2-mm spot size was 2,865 J/cm2 without compression and 2,674 J/cm2 with compression. With the 3-mm spot size, the threshold fluence of 1,528 J/cm2 was not affected by compression. Histopathologic studies showed transretinal damage at the lowest levels necessary to achieve angiographic evidence of a treatment lesion or a barely visible funduscopic lesion at the time of treatment.


CONCLUSIONS
Nonpigmented rabbits required more than a 12-fold increase in total TTT fluence compared with pigmented rabbits with the 2-mm spot size and a ninefold increase with the 3-mm spot size. Inner and outer retinal damage was seen histopathologically at these levels.
Peyman
Gholam A
GA
Department of Ophthalmology, Tulane University Health Sciences Center, New Orleans, Louisiana 70112-2699, USA. mchiass1@tulane.edu
Genaidy
Mahmoud
M
Moshfeghi
Darius M
DM
Ghahramani
Fatemah
F
Yoneya
Shin
S
Men
Gamze
G
Kuo
Po-Cheng
PC
Bezerra
Yanno
Y
Nishiyama-Ito
Yoko
Y
D000818:Animals; D001831:Body Temperature; D005131:Eye Injuries / Q000209:etiology* / Q000473:pathology; D005451:Fluorescein Angiography; D006979:Hyperthermia, Induced; D017075:Laser Coagulation / Q000009:adverse effects*; D023421:Models, Animal; D009887:Ophthalmoscopy; D010857:Pigment Epithelium of Eye / Q000502:physiology*; D011680:Pupil; D011817:Rabbits; D011836:Radiation Tolerance; D012160:Retina / Q000293:injuries* / Q000473:pathology / Q000601:surgery; D012164:Retinal Diseases / Q000209:etiology* / Q000473:pathology; D012684:Sensory Thresholds; D013997:Time Factors