TECHNIQUE OF LASER CHORIORETINAL ANASTOMOSIS CREATION IN CENTRAL RETINAL VEIN OCCLUSION AND SUCCESS RATE WITH A NEW PHOTOCOAGULATOR SYSTEM.

PURPOSE: To evaluate the success rate of laser chorioretinal anastomosis (L-CRA) creation with a new laser photocoagulator system capable of 5 watts (W) power in patients with central retinal vein occlusion (CRVO). METHODS: Patients with a treatment-naive CRVO were enrolled as part of an ongoing trial combining L-CRAs with anti-vascular endothelial growth factor treatment. RESULTS: Thirty-three patients were treated with an L-CRA developing in 29 (88%). Mean power was 2.7 W and mean time for development was 1.8 months. Each patient had two potential sites created. Eighteen patients developed 2 L-CRAs and the remaining 11 patients, one each. Of the 66 potential sites, successful L-CRAs developed at 47 sites (71%). Additional Nd:YAG laser applications were used in 39% of sites. Mean follow-up was 23 months and no significant complications were seen. CONCLUSION: An L-CRA as a means of permanently bypassing the obstruction to venous outflow in CRVO may become more relevant as not all patients respond well to intravitreal therapy. The limitation to this technique in the past has been lack of availability of a laser system with the power necessary to create the L-CRA. The success rate with the new system has improved to 88% representing a significant improvement over our original success rate of 33%.

Nanosecond pulse lasers for retinal applications.

BACKGROUND AND OBJECTIVES: Thermal lasers are routinely used to treat certain retinal disorders although they cause collateral damage to photoreceptors. The current study evaluated a confined, non-conductive thermal, 3-nanosecond pulse laser in order to determine how to produce the greatest therapeutic range without causing collateral damage. Data were compared with that obtained from a standard thermal laser. MATERIALS AND METHODS: Porcine ocular explants were used; apposed neuroretina was also in place for actual laser treatment. After treatment, the retina was removed and a calcein-AM assay was used to assess retinal pigmented epithelium (RPE) cell viability in the explants. Histological methods were also employed to examine lased transverse explant sections. Three nanoseconds pulse lasers with either speckle- or gaussian-beam profile were employed in the study. Comparisons were made with a 100 milliseconds continuous wave (CW) 532 nm laser. The therapeutic energy range ratio was defined as the minimum visible effect threshold (VET) versus the minimum detectable RPE kill threshold. RESULTS: The 3-nanosecond lasers produced markedly lower minimum RPE kill threshold levels than the CW laser (e.g., 36 mJ/cm(2) for speckle-beam and 89 mJ/cm(2) for gaussian-beam profile nanosecond lasers vs. 7,958 mJ/cm(2) for CW laser). VET values were also correspondingly lower for the nanosecond lasers (130 mJ/cm(2) for 3 nanoseconds speckle-beam and 219 mJ/cm(2) for gaussian-beam profile vs. 1,0346 mJ/cm(2) for CW laser). Thus, the therapeutic range ratios obtained with the nanosecond lasers were much more favorable than that obtained by the CW laser: 3.6:1 for the speckle-beam and 2.5:1 for the gaussian-beam profile 3-nanosecond lasers versus 1.3:1 for the CW laser. CONCLUSIONS: Nanosecond lasers, particularly with a speckle-beam profile, provide a much wider therapeutic range of energies over which RPE treatment can be performed, without damage to the apposed retina, as compared with conventional CW lasers. These results may have important implications for the treatment of retinal disease.

Rapid and delayed death of cultured trabecular meshwork cells after selective laser trabeculoplasty.

BACKGROUND AND OBJECTIVE: Selective laser trabeculoplasty (SLT) is becoming increasingly employed to reduce elevated intraocular pressure in glaucoma patients. SLT is known to target the ocular trabecular meshwork (TM), but the exact response mechanisms to this treatment have not been clearly delineated. The aim of the present study, therefore, was to investigate the modes of death of cultured bovine TM cells subjected to SLT in vitro. MATERIALS AND METHODS: Bovine TM cell cultures were established, pigmented with exogenous melanin and irradiated with a Q-switched, frequency doubled, Nd:YAG laser, at different energy settings (0.05-1.0 mJ). Influences on cells were determined for up to 10 days post-treatment by trypan blue exclusion, terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) and by morphological assessment. Furthermore, homogeneous mixtures of pigmented and non-pigmented TM cells were irradiated to ascertain selectivity of laser effects. RESULTS: At higher energy levels (1.0, 0.75 mJ), immediate loss of cells was detected at the irradiated site. Trypan blue exclusion analysis showed that necrotic cell death subsequently occurred up to 8 hours following irradiation, peaking at 60 minutes. This was followed by delayed cell death peripheral to the irradiated area which was characteristic of apoptosis and which peaked at 2-3 days post-treatment. When mixed cultures were tested, laser treatment selectively killed pigmented cells at an energy level equivalent to the lower cell killing threshold in the initial studies (0.2 mJ) but at the higher laser energy of 0.35 mJ, all cells were non-selectively killed. CONCLUSIONS: SLT treatment killed pigmented TM cells in culture by a variety of processes (instant vaporization, rapid necrosis, delayed apoptosis), depending on the magnitude of the energy used and the distance from the center of the irradiated zone. These data may assist in the elucidation of the mechanism of action of the SLT procedure on TM cells in situ.