Abstract
Purpose: :
The laser energy required for retinal laser therapy is highly variable between different individuals. To ensure treatment success and avoid unnecessary damage to the retina it is crucial to choose the right energy settings. We evaluated the effect of patient-related factors on the laser energy required to produce a mild laser burn in patients with diabetic macular edema who are treated with focal or grid photocoagulation using the NAVILAS® laser system.
Methods: :
22 patients were treated with NAVILAS® 532nm laser which is a semi-automated computer controlled laser system. Prior to the treatment the following parameters were examined: refraction, axial length (IOL-Master, Zeiss), retinal and choroidal thickness (Spectralis OCT, Heidelberg Engineering), phakic or pseudophacic lens status, opacity of crystalline lens (measured by Pentacam, Oculus) and iris pigmentation (used as surrogate parameter for fundus pigmentation). The location of spots, spot size (100μm) and pulse duration (100ms) were preplanned on a fluorescein angiography which was performed on the NAVILAS® system. During the laser treatment, the treatment plan is overlayed with a live fundus image and the laser beam is automatically stabilized on the planned treatment spots. Laser energy was increased stepwise until a mild burn was achieved. This energy was used for treatment.
Results: :
36 eyes of 23 patients were included in the study. Axial length, refraction, retinal thickness, choroidal thickness and lens densitometry scores in phakic patients did not correlate with the energy needed to achieve a mild burn. There was no significant difference in laser energy between eyes with light or dark iris. Pseudophakic patients needed 11,9mW less energy than phakic eyes (70,9mW versus 82,8mW) which is significant at the 0.05 level.
Conclusions: :
Significantly less laser energy was needed for pseudophakic eyes than for phakic eyes to achieve the same burn intensity. Regarding the mean patients’ age of 63 years this difference seems plausible as the aging crystalline lens leads to an increase in light absorption and scattering. Iris colour did not influence laser energy which might be due to a lack of correlation of iris pigmentation with fundus pigmentation in our caucasian study population. No significant association of laser energy to any other factor could be found.
Keywords: laser • diabetic retinopathy • edema