Relationship between intensity of reflected light and temperature increase: assessment of fundus pigmentation for transpupillary thermotherapy

PURPOSE

To develop a new device for measuring reflected light during diode-laser irradiation in transpupillary thermotherapy (TTT) and to assess the correlation between fundus pigmentation, the measured intensity of reflected light, and the increase in fundus temperature.

METHODS

We developed a device to measure reflected light by modifying a slit-lamp-mounted 810-nm diode-laser delivery system used clinically for TTT. The diode laser was used to irradiate test charts with various degrees of reflectance in in vitro experiments, and the fundus of nonpigmented or pigmented rabbits in in vivo experiments; then, the intensity of the reflected light and the temperature increase at the target were measured. The retinal sections were also examined histologically.

RESULTS

There was a significant negative correlation between the intensity of the reflected light and the temperature increase in the target that depended on the degree of reflectance of the charts or the pigmentation of the rabbit eyes. On histopathologic examination, the extent of the changes in the irradiated retina after TTT was clearly different between pigmented and nonpigmented rabbits.

CONCLUSIONS

Correlations between fundus pigmentation, the intensity of reflected light during diode-laser irradiation, and the temperature increase in TTT were demonstrated in vitro and in vivo. Our results suggest that measurement of the intensity of reflected light should be helpful for modulating the laser power in TTT according to the degree of fundus pigmentation.

Emerging drugs for age-related macular degeneration

Age-related macular degeneration (AMD) is a leading cause of blindness that until recently had no recognised drug treatment. In wet AMD, choroidal neovascularisation (CNV) causes a profound loss of central vision. CNV is a complex process in which tissue ischaemia and/or inflammation is thought to trigger production of angiogenic signal molecules. The release of VEGF appears to be particularly important. Verteporfin photodynamic therapy was the first drug therapy to be licensed for the treatment of some types of wet AMD. Other treatments directly targeting VEGF or other aspects of angiogenesis, such as pegaptanib, ranibizumab and anecortave acetate, have either recently been licensed or are in the advanced stages of development. These and other promising treatment options such as combination strategies are reviewed.

Noninvasive optoacoustic online retinal temperature determination during continuous-wave laser irradiation

The therapeutic effect of most retinal laser treatments is initiated by a transient temperature increase. Although crucial to the effectiveness of the treatment, the temperature course is not exactly known due to individually different tissue properties. We develop an optoacoustic method to determine the retinal temperature increase in real time during continuous-wave (cw) laser irradiation, and perform temperature calculations to interpret the results exemplary for transpupillary thermotherapy (TTT). Porcine globes ex vivo and rabbit eyes in vivo are irradiated with a diode laser (lambda=810 nm, P< or =3 W, phi=2 mm) for 60 s. Simultaneously, pulses from a N2-laser pumped dye laser (lambda=500 nm, tau=3.5 ns, E approximately 5 microJ) are applied on the retina. Following its absorption, an ultrasonic pressure wave is emitted, which is detected by a transducer embedded in a contact lens. Using the previously measured temperature-dependent Gruneisen coefficient of chorioretinal tissue, a temperature raise in porcine eyes of 5.8 degrees C(Wcm2) after 60 s is observed and confirmed by simultaneous measurements with an inserted thermocouple. In a rabbit, we find 1.4 degrees C(Wcm2) with, and 2.2 degrees C(Wcm2) without perfusion at the same location. Coagulation of the rabbit's retina occurs at DeltaT=21 degrees C after 40 s. In conclusion, this optoacoustic method seems feasible for an in vivo real-time determination of temperature, opening the possibility for feedback control retinal laser treatments.

Transpupillary thermotherapy for subfoveal leaks in central serous chorioretinopathy

AIM

To evaluate transpupillary thermotherapy (TTT) for the treatment of subfoveal focal leaks in central serous chorioretinopathy (CSC).

METHODS

The patients presenting with long-standing CSC, but without the features of chronicity, were offered the options of TTT, photodynamic therapy (for subfoveal leaks), photocoagulation (for extrafoveal leaks), or observation. The patients who opted for TTT or observation were enrolled in this study. TTT was performed using a spot diameter of 0.5 mm for 1 min. Best-corrected visual acuity (BCVA), status of macular detachment, and fluorescein angiographic status were evaluated at 1, 3, and 6 months.

RESULTS

This study included 39 patients (40 eyes) with CSC between 4 and 12 months, of whom 25 patients (25 eyes) opted for TTT for subfoveal leaks. Fourteen patients (15 eyes) were followed up without treatment. The groups were comparable in age, sex, and baseline BCVA. Minimum follow-up was 6 months. Within 3 months, TTT resulted in the resolution of the serous detachment in 24 (96%) eyes with a single session; one eye required a repeat treatment. Eight control eyes demonstrated persisting CSC at the last follow-up. Visual acuity improved in 23 (92%) treated and five (33%) control eyes; the difference in outcome was statistically significant (P<0.001). One case developed choroidal neovascularization, which resolved with visual recovery to 20/20 after repeat-TTT.

CONCLUSION

TTT resulted in the resolution of CSC with subfoveal angiographic leaks with significant improvement in visual outcome, in comparison to the natural history of persistent CSC.