Semiconductor diode laser photocoagulation in retinal vascular disease

Laser Treatment for Diabetic Retinopathy: History, Mechanism, and Novel Technologies

Background: Diabetic retinopathy (DR), as a complication of diabetes mellitus (DM), remains a significant contributor to preventable vision impairment in the working-age population. Laser photocoagulation is essential in treating DR in conjunction with anti-vascular endothelial growth factor (VEGF) injection, steroids, and vitrectomy. This review summarizes the history of laser photocoagulation and highlights its current role and long-term effectiveness in real-world conditions. Methods: The National Clinical Trial (NCT), PubMed, Google Scholar, and China National Knowledge Infrastructure (CNKI) databases were searched utilizing combined or individual keywords, and a total of 121 articles were reviewed by the authors. Results: Several novel laser photocoagulation technologies, such as patterned scanning laser, subthreshold micropulse laser, navigated laser, multimodal imaging-guided laser, and retina rejuvenation therapy, substantially decrease the adverse effects and improve the accuracy and security of laser therapy. Numerous studies have demonstrated the outstanding clinical efficacy of combination therapies with pharmacologic treatments like anti-VEGF in treating DR and diabetic macular edema (DME). A 20-year follow-up retrospective study in our center preliminarily demonstrated the long-term effectiveness of conventional laser photocoagulation. Conclusions: More clinical trials are required to confirm the clinical effectiveness of novel laser technologies. Better treatment protocols for the combination therapy may be detailed. Anti-VEGF treatment has better effects, especially for DME and in a short period. But in real-world conditions, given the long-term effectiveness and economic advantages of conventional laser treatment, it should be prioritized over anti-VEGF injection in certain situations.

Patient Comfort with Yellow (577 nm) vs. Green (532 nm) Laser Panretinal Photocoagulation for Proliferative Diabetic Retinopathy

PURPOSE

Pain associated with panretinal photocoagulation (PRP) can adversely affect the number and quality of retinal burns delivered and subsequently increase the number of treatment sessions required to achieve regression of proliferative diabetic retinopathy (PDR). We assessed comfort in patients undergoing treatment with yellow (577 nm) vs. green (532 nm) PRP for PDR.

DESIGN

Prospective, single-center, randomized crossover clinical trial.

SUBJECTS

Patients with PDR with high-risk characteristics.

METHODS

Subjects were equally randomized to first receive PRP with a laser indirect ophthalmoscope with either green (IQ 532; IRIDEX, Mountain View, CA) or yellow (IQ 577; IRIDEX) laser, followed by additional treatment with the opposite laser using standardized settings in the superior hemisphere of a single treatment eye per patient. Topical anesthetic was used in all study eyes before each treatment and power was titrated until moderate grey-white retinal burns were achieved.

MAIN OUTCOME MEASURES

The primary outcome measure was patient's perceived pain as measured with a standardized 10-point pain scale. Secondary outcome measures included laser power, treatment time, number of treatment shots with each laser, and physician ease-of-use score with each laser on a 10-point scale.

RESULTS

Forty patients (40 eyes) with a mean age of 54.0 years were enrolled. Mean pain scores were similar when comparing treatment with yellow and green laser (3.1 ± 2.3 vs. 2.8 ± 2.6; P = 0.40). No significant difference was seen in visual acuity (P = 0.44) or central macular thickness (P = 0.39) 1 month after PRP. Additionally, there were no significant differences when comparing minimum power required (243.2 ± 74.2 vs. 234.0 ± 59.6 mW; P = 0.55), treatment time (5.1 ± 3.6 vs. 5.6 ± 3.9 minutes; P = 0.384), and number of treatment shots (257.6 ± 12.6 vs. 258.0 ± 2.3; P = 0.68). Six of 7 co-investigators (85%) preferred using yellow laser over green and reported ease-of-use scores of 9.0 ± 1.2 and 7.6 ± 1.4, respectively (P = 0.07). No severe adverse events occurred.

CONCLUSIONS

Patient comfort during PRP for PDR utilizing laser indirect ophthalmoscopy is similar for green and yellow wavelengths.

Micropulsed diode laser therapy: evolution and clinical applications

Many clinical trials have demonstrated the clinical efficacy of laser photocoagulation in the treatment of retinal vascular diseases, including diabetic retinopathy. There is, however, collateral iatrogenic retinal damage and functional loss after conventional laser treatment. Such side effects may occur even when the treatment is appropriately performed because of morphological damage caused by the visible endpoint, typically a whitening burn. The development of the diode laser with micropulsed emission has allowed subthreshold therapy without a visible burn endpoint. This greatly reduces the risk of structural and functional retinal damage, while retaining the therapeutic efficacy of conventional laser treatment. Studies using subthreshold micropulse laser protocols have reported successful outcomes for diabetic macular edema, central serous chorioretinopathy, macular edema secondary to retinal vein occlusion, and primary open angle glaucoma. The report includes the rationale and basic principles underlying micropulse diode laser therapy, together with a review of its current clinical applications.

Retina remodeling following diode laser

BACKGROUND

The purpose of this study was to characterize the sequential development of focal and surround retinal injury and repair following transscleral diode laser to rat retina.

METHODS

Transscleral laser photocoagulation of the retina was induced with a diode laser (DioPexy Probe, 810 nm, 200 mW, 2 seconds) in adult Long-Evans rats. The right eye of rats with survival times of 0 days (n = 4), 5 days (n = 6), 2 weeks (n = 4), 6 weeks (n = 6), and 12 weeks (n = 4) was studied. Using serial sections, detailed pathological changes in laser-treated and surrounding retinal and choroidal areas were compared with the control fellow eye.

RESULTS

Photocoagulation damage was limited to the retina, sparing Bruch's membrane, with minimal choroidal involvement in almost all cases (23/24 eyes). Following damage to the neural retina, the sequence of major remodeling processes was consistent and included inflammatory response, reparative changes, and formation of glial-vascular scar with neovascularization.

INTERPRETATION

This new laser model caused reproducible injury, inflammation, and scarring confined to the retina, and may be a tool to help test the effects of candidate neuroprotective/regenerative agents on retinal degeneration to prevent vision loss.

Comparative evaluation of diode laser versus argon laser photocoagulation in patients with central serous retinopathy: a pilot, randomized controlled trial [ISRCTN84128484]

BACKGROUND

To evaluate the efficacy of diode laser photocoagulation in patients with central serous retinopathy (CSR) and to compare it with the effects of argon green laser.

METHODS

Thirty patients with type 1 unilateral CSR were enrolled and evaluated on parameters like best corrected visual acuity (BCVA), direct and indirect ophthalmoscopy, amsler grid for recording scotoma and metamorphopsia, contrast sensitivity using Cambridge low contrast gratings and fluorescein angiography to determine the site of leakage. Patients were randomly assigned into 2 groups according to the statistical random table using sequence generation. In Group 1 (n = 15), diode laser (810 nm) photocoagulation was performed at the site of leakage while in Group 2 (n = 15), eyes were treated with argon green laser (514 nm) using the same laser parameters. Patients were followed up at 4, 8 and 12 weeks after laser.

RESULTS

The mean BCVA in group 1 improved from a pre-laser decimal value of 0.29 +/- 0.14 to 0.84 +/- 0.23 at 4 weeks and 1.06 +/- 0.09 at 12 weeks following laser. In group 2, the same improved from 0.32 +/- 0.16 to 0.67 +/- 0.18 at 4 weeks and 0.98 +/- 0.14 at 12 weeks following laser. The improvement in BCVA was significantly better in group 1 (p < 0.0001) at 4 weeks. At 4 weeks following laser, all the patients in group1 were free of scotoma while 6 patients in group 2 had residual scotoma (p < 0.05). The mean contrast sensitivity in group 1 improved from pre-laser value of 98.4 +/- 24.77 to 231.33 +/- 48.97 at 4 weeks and 306.00 +/- 46.57 at 12 weeks following laser. In group 2, the same improved from 130.66 +/- 31.95 to 190.66 +/- 23.44 at 4 weeks and 215.33 +/- 23.25 at 12 weeks. On comparative evaluation, a significantly better (p < 0.001) improvement was noted in group 1.

CONCLUSION

Diode laser may be a better alternative to argon green laser whenever laser treatment becomes indicated in patients with central serous retinopathy in terms of faster visual rehabilitation and better contrast sensitivity. In addition, diode laser also has the well-recognized ergonomic and economic advantages.

Effects of transcorneal iridal photocoagulation on the canine corneal endothelium using a diode laser

OBJECTIVE

To investigate the potential damage to the canine corneal endothelium following transcorneal iridal laser photocoagulation using a semiconductor diode laser.

ANIMALS STUDIED

Sixteen young mongrel dogs.

PROCEDURES

Baseline corneal endothelial cell counts and corneal thickness were measured in the central and temporal quadrants using a noncontact specular microscope under general anesthesia. Transcorneal iridal photocoagulation was applied using a semiconductor diode laser in a continuous mode with the use of an operating microscope. Fifteen dogs were treated, and the sixteenth dog served as a control. Fifteen different treatment combinations were randomly assigned to the 30 eyes; the fellow eye was treated differently. Three treatment factors were investigated: (1) laser energy intensity, (2) target tissue to endothelial distance, and (3) laser application duration. After 3 weeks the dogs were euthanized, specular microscopy was repeated, and the cornea was examined by scanning electron microscopy.

RESULTS

Dyscoria and focal iris darkening were noted in all eyes immediately following laser treatment. Focal corneal edema (n = 2) and an incipient anterior capsular cataract (n = 1) were also noted. Baseline mean corneal endothelial cell densities were 2530 cells/mm2 centrally and 2607 cells/mm2 temporally. Postlaser corneal endothelial cell densities were 2499 cells/mm2 centrally and 2523 cells/mm2 temporally. Mean prelaser corneal thickness measurements were 0.555 mm centrally and 0.549 mm temporally. Postlaser corneal thickness measurements were 0.580 mm centrally and 0.554 mm temporally. Statistical analyzes revealed no significant changes in endothelial cell densities (P > 0.05) or corneal thickness (P > 0.05) induced by any treatment combination. Aside from tissue handling and processing artifacts, scanning electron microscopy revealed no endothelial cell damage.

CONCLUSIONS

Our study demonstrated by specular and scanning electron microscopy that diode laser iridal photocoagulation had no significant effect on the canine corneal endothelium within the parameters described. However, one must take into consideration the young age of the dogs and the potential for corneal endothelial cell regeneration in young dogs, and the relatively short period of postoperative study.

Transpupillary retinopexy of chorioretinal lesions predisposing to retinal detachment with the use of diode (810 nm) microlaser

PURPOSE

To evaluate the clinical efficacy and safety of diode microlaser for transpupillary retinopexy in eyes with retinal degenerations and retinal tears in a prospective clinical study.

METHODS

Twenty eyes (19 patients) with mid or peripheral degenerations and retinal tears were treated with infrared diode photocoagulation. A continuous-wave diode laser was used to create clinically just visible chororetinal bums. The follow-up period was extended to 3 months. Color photographs of the coagulated retina were taken 24 hours after laser retinopexy and at 1 month and 3 months postoperatively.

RESULTS

Acute chorioretinal burns appeared gray-white on the midperiphery, not sharply defined and sometimes somewhat difficult to detect during photocoagulation. Power levels ranged from 110 to 640 mW (mean +/- SD 384+/-133.47 mW). In eyes with dark brown irises, the mean laser power was significantly lower than in eyes with blue-green irises (325.83+/-117.90 mW versus 471.25+/-109.60 mW, P < 0.05). At the 1 -month postoperative follow-up examination, all eyes showed chororetinal scarring with pigmentary mottling. At 3 months, the diode lesions' appearance was that of a marked atrophic chonoretinal scar. There were no adverse side effects in the laser-treated eyes except for a small choroidal-retinal-vitreal bleeding in 1 (5%) of the eyes.

CONCLUSIONS

Transpupillary photocoagulation to mid or peripheral retina with diode microlaser has proven to be effective at providing retinopexy of retinal degenerations and retinal tears. The long wave 810 nm can also be used successfully and safely for the prophylaxis of retinal detachment because it can create a strong adhesion between the retina and choroid. However, diode laser should not be employed routinely for treating patients with clear media or fundus hypopigmentation. The use of diode is preferably indicated in eyes with media opacities because infrared light has the advantage of a better transmission through lens opacity or vitreous hemorrhage. As diode laser energy can produce variable tissue effects, there may be some difficulty in obtaining reproducible bums because of unpredictable changes in melanin density of the retinal pigment epithelium and choroid.

Diode laser transscleral retinopexy in rhegmatogenous retinal detachment surgery

PURPOSE

To evaluate the safety and efficacy of transscleral diode laser for retinopexy in rhegmatogenous retinal detachment surgery.

METHODS

Conventional retinal detachment surgery with transscleral diode laser retinopexy was performed on 52 eyes of 52 patients (22 female, 30 male), aged from 12 to 74 years (mean 51 + 4.1).

RESULTS

Of the 52 eyes 36 (69%) were reattached in a single operation and adequate chorioretinal scars were achieved in 34 of them. Additional transpupillary laser photocoagulation was performed in two cases in the postoperative period. Retinal re-attachment was achieved with exoplant revision and transscleral laser retinopexy in six cases (12%). Ten cases (19%) with severe PVR were reattached with vitreoretinal surgery.

CONCLUSIONS

Transscleral diode laser retinopexy was an effective and safe method, with accurate lesion location, concurrent permanent laser marks on the retina, and easy transmission through the extraocular muscles and solid buckling elements. Minor complications were minimized by gaining experience with the technique.

Thermal modelling of micropulsed diode laser retinal photocoagulation

BACKGROUND AND OBJECTIVE

Recent studies have sought to utilize diode laser "micropulsing" in order to preserve therapeutic efficacy of retinal photocoagulation while minimizing pain and subjacent tissue injury. A model for the transient thermal tissue response to continuous and micropulsed diode laser output is presented in order to understand the laser-tissue interactions and to generate optimum parameters for exploiting potential advantages of micropulsed application.

STUDY DESIGN/MATERIALS AND METHODS

The tissue thermal response was calculated by convolving the analytical solution to the three-dimensional, isotropic heat conduction equation with a source term corresponding to the spot size of the laser incident on the absorbing retinal pigment epithelium (RPE) and choroid layers of the ocular fundus. Thermal localization is quantitated by comparing the temperature rise in the RPE (T(RPE) and deep choroid (T(Ch). A 1-watt (average power), 20-microns diameter, 100 ms pulse (continuous or micropulsed) of 810 nm radiation was modelled to be incident on a geometric idealization of the human retina and choroid.

RESULTS

A temperature gradient is rapidly established with only modest temperature augmentation between 10 and 100 ms. At 100 ms T(RPE) and T(Ch) are 32 and 23 C, respectively, for continuous application, and 41 and 27 C for 2 ms on/off micropulsed application. For a duty factor (total laser "on" time divided by pulse length) of 50%, T(RPE)/T(Ch) is maximal for a micropulse on/off duration of 2 ms; however, the variation over micropulse durations from 200 microseconds to 50 ms is small. In addition, whereas end-pulse T(RPE)/T(Ch) is greater for 2 ms on/off application when compared with continuous delivery (1.53 vs. 1.39), thermal relaxation during pulse quiescence in the micropulsed mode allows for an early increase in deep choroidal temperature with respect to T(RPE). For ten 200 microseconds pulses equally separated over 100 ms (duty factor = 2%), T(RPE)/T(Ch) = 3.2. With more numerous, lower power micropulses, T(RPE)/T(Ch) decreases monotonically to 1.39 as the duty factor is increased to 100%.

CONCLUSION

These modelling studies provide the first quantitative predictions of thermal localization achieved with diode laser micropulsing and demonstrate that short pulse lengths and low duty factors allow for maximum thermal localization. These studies will potentiate pulse-shape optimization strategies for diode laser retinal photocoagulation applications.

Image processing algorithms for retinal montage synthesis, mapping, and real-time location determination

Although laser retinal surgery is the best available treatment for choridal neovascularization, the current procedure has a low success rate (50%). Challenges, such as motion-compensated beam steering, ensuring complete coverage and minimizing incidental photodamage, can be overcome with improved instrumentation. This paper presents core image processing algorithms for 1) rapid identification of branching and crossover points of the retinal vasculature; 2) automatic montaging of video retinal angiograms; 3) real-time location determination and tracking using a combination of feature-tagged point-matching and dynamic-pixel templates. These algorithms tradeoff conflicting needs for accuracy, robustness to image variations (due to movements and the difficulty of providing steady illumination) and noise, and operational speed in the context of available hardware. The algorithm for locating vasculature landmarks performed robustly at a speed of 16-30 video image frames/s depending upon the field on a Silicon Graphics workstation. The montaging algorithm performed at a speed of 1.6-4 s for merging 5-12 frames. The tracking algorithm was validated by manually locating six landmark points on an image sequence with 180 frames, demonstrating a mean-squared error of 1.35 pixels. It successfully detected and rejected instances when the image dimmed, faded, lost contrast, or lost focus.

The treatment of macular disease using a micropulsed and continuous wave 810-nm diode laser

OBJECTIVE

The purpose of the study is to determine whether the 810-nm diode wavelength using a rectangular waveform is clinically effective in the treatment of choroidal neovascularization from age-related macular degeneration and to determine whether macular edema secondary to branch vein occlusion or diabetic retinopathy can be effectively treated with this laser using the micropulse waveform.

DESIGN

Review of consecutive nonrandomized patients whose eyes were treated with the diode laser over a 30-month period.

PARTICIPANTS

Fifty-three patients with an initial presentation of choroidal neovascularization located subfoveally (77%), extrafoveally (17%), and juxtafoveally (6%); 14 patients with macular edema from a branch vein occlusion; and 59 patients with diabetic macular edema, 40 of which were treated for the first time.

INTERVENTION

Ablative rectangular wave laser photocoagulation was applied to the choroidal neovascular membranes and very light threshold treatment was applied in a macular grid to treat retinal edema. Microaneurysms were not targeted.

MAIN OUTCOME MEASURES

Anatomic resolution of macular edema or choroidal neovascularization and visual acuity.

RESULTS

Sixty percent of eyes treated for choroidal neovascularization had no persistence or recurrence at 6 months, and 72% achieved visual stabilization. In 8% of eyes, some localized bleeding occurred during photocoagulation. Clinical resolution of macular edema from branch vein occlusion occurred by 6 months in 92% of eyes, and 77% had stabilization of visual acuity. At 6 months, 76% of newly treated patients with diabetic macular edema and 67% of previously treated patients had clinical resolution of their edema. Vision was improved or stabilized in 91% and 73% of newly treated and retreated patients at 6 months, respectively.

CONCLUSIONS

The micropulsed 810-nm diode laser is clinically effective in the treatment of macular edema from venous occlusion and diabetic retinopathy, and the rectangular (normal) mode diode laser can be used in many eyes with choroidal neovascularization.

Diode laser contact transscleral retinal photocoagulation: a clinical study

AIM

To examine the clinical efficacy of contact transscleral retinal photocoagulation with a diode laser.

METHODS

Transscleral retinal photocoagulation was performed on 36 eyes. The conditions treated included peripheral retinal breaks associated with retinal detachments (30 eyes) and giant retinal tears (six eyes). Of the 30 eyes with retinal detachments, 28 underwent transscleral photocoagulation to the site of drainage of subretinal fluid in an attempt to reduce the risk of hemorrhage.

RESULTS

Threshold lesions were obtained with irradiances of between 95.4 W/cm2 and 191 W/cm2. Satisfactory chorioretinal adhesion was achieved in all eyes with retinal breaks and giant retinal tears. The only significant complications of treatment encountered were punctate choroidal haemorrhages (three eyes). Drainage related choroidal haemorrhage following earlier photocoagulation occurred in two of 28 eyes.

CONCLUSIONS

This study confirms the clinical potential of transscleral diode laser photocoagulation in the therapy of surgical retinal conditions.

Laser energy and dye fluorescence transmission through blood in vitro

PURPOSE

Because of the potential usefulness of evaluating and treating choroidal neovascularization obscured by blood, we designed this study to quantify the transmission of dye fluorescence and laser energy through blood.

METHODS

Blood preparations anticoagulated with ethylenediaminetetraacetic acid with hematocrits of 0% (plasma), 46%, and 99% were placed in open cuvettes with path lengths of 100, 200, or 500 microns and were exposed for one minute to either 100% oxygen or 100% carbon dioxide. Each cuvette was then sealed. Photographs of the cuvettes of blood in front of a flask of fluorescein or indocyanine green solution were decoded and used to calculate the percent transmission of fluorescence through blood. Cuvettes of blood were also placed in the path of argon, krypton, and diode lasers for energy transmission measurements.

RESULTS

Plasma transmission of fluorescein and indocyanine green fluorescence and argon, krypton, and diode laser energy was 89% to 100% for all samples tested. Transmission of fluorescein fluorescence and argon laser energy through 99% hematocrit samples were both less than 5%. Transmission of indocyanine green fluorescence through 100-, 200-, and 500-microns-thick cuvettes filled with 99% hematocrit blood was 57%, 34%, and 4%. Transmission of krypton laser energy was 50%, 25%, and 6%; and transmission of diode laser energy was 60%, 35%, and 12% through 99% hematocrit blood. Intermediate transmission values were obtained for 46% hematocrit samples.

CONCLUSIONS

Krypton and, to a slightly greater degree, diode laser energy penetrate a thin film of blood. Indocyanine green fluorescence also penetrates a thin film of blood. If a layer of blood appears thinner than 500 microns, then indocyanine green angiography may be useful in imaging underlying pathologic features. If a lesion can be imaged with indocyanine green, then it can probably be treated with a krypton or diode laser.

Lasers in ophthalmology

This article reviews the principle uses of ophthalmic lasers, providing historical background with an emphasis on new applications and areas of investigation. Ophthalmic photocoagulation was the first medical laser application and has restored or maintained vision in millions of people. More recently, photodisruption and, increasingly, ablation have gained prominence for treating a wide range of ocular pathology. The unique properties of lasers have also been harnessed for diagnostic purposes, with optical coherence tomography representing a significant improvement over existing imaging methods. Many ophthalmic applications of lasers have been developed, but the field is a dynamic one which continues to evolve along with laser technology itself.

Erbium:YAG laser photothermal retinal ablation in enucleated rabbit eyes

The erbium:YAG laser has been shown to produce precise tissue ablation because of the high water absorption of the 2.94-microns wave-length emitted by this laser. We used an experimental system to create lesions of various depths in the surface of the rabbit retina in enucleated eyes in vitro to examine the potential application to maneuvers such as retinotomy and the removal of epiretinal membranes in vitrectomy. With an air/retinal interface, single pulses produced discrete craters in the retinal surface with a depth proportional to fluence, ranging from 30 microns for a pulse of 1.3 J/cm2 to a full-thickness retinotomy at 3.9 J/cm2. An adjacent zone of coagulated tissue ranging in size from 15 to 40 microns was noted. Multiple pulses had an additive effect. With a fluid/retinal interface, 20 pulses of 3.6 J/cm2 produced a full-thickness retinotomy, with an adjacent zone of damaged tissue up to 1 mm, caused by effects of volatilization of intervening fluid. The erbium:YAG laser may have a role in vitreoretinal surgery.

Intraretinal leakage of indocyanine green dye

PURPOSE

Indocyanine green (ICG) dye is known to remain selectively in and around choroidal neovascularization (CNV) associated with age-related macular degeneration, and is thought to be cleared from the overlying retinal circulation without leakage. This is the basis of ICG dye-enhanced laser photocoagulation. The authors have observed, however, leakage of ICG dye into cystoid spaces within the retinal and have determined the incidence, clinical features, and angiographic characteristics of this newly described phenomenon.

METHODS

The digital ICG videoangiograms of 149 consecutive patients with exudative age-related macular degeneration and occult CNV were reviewed independently to determine the characteristics of intraretinal ICG dye leakage.

RESULTS

Of the 149 patients with occult CNV, 16 (11%) demonstrated intraretinal leakage of ICG dye between 14 and 34 minutes (median = 20 minutes). The clinical features most commonly associated with this phenomenon are: subretinal fluid (88%), subretinal hemorrhage (88%), subretinal lipid (63%), and retinal pigment epithelial detachment (56%).

CONCLUSIONS

Indocyanine green dye may not be as concentrated in and around CNV as previously reported. The delayed onset of its appearance within intraretinal cystoid spaces may suggest a diffusible choroidal source of leakage. Intraretinal ICG dye may be a relative contraindication for ICG dye-enhanced laser photocoagulation.

Indocyanine green enhanced diode laser photocoagulation of subretinal neovascular membranes

Images

Dye enhanced laser photocoagulation in the treatment of a peripapillary subretinal neovascular membrane

A 45-year-old female with an elevated peripapillary subretinal neovascular membrane was treated with dye enhanced laser photocoagulation, using indocyanine green and the diode laser. Following treatment the membrane regressed, with flattening of the lesion. No side effects occurred and excellent visual acuity was maintained over a 12 month follow-up period.

Diode lasers in ophthalmology

Compact laser emitting diodes of gallium-aluminium-arsenide are now available for incorporation into clinical lasers in ophthalmology. These lasers are cheap and have low running costs. They are portable and their wavelength of emission (810 nm) may be advantageous in certain clinical situations. Clinical trials in retinal vascular disease, trabeculoplasty, and cyclophotocoagulation, have been encouraging. Recent advances allow laser delivery through binocular indirect ophthalmoscopes, endolaser and contact transscleral probes in addition to slit lamp mounted versions. Laser delivery in situations which were previously impossible has immense implication for prevention of blindness due to glaucoma and retinal vascular disease throughout the world.

Diode laser for retinopathy of prematurity--early outcome

Diode laser treatment for retinopathy of prematurity was successful in 81% of 21 eyes with 'threshold' (zone 2, stage 3+) disease. This compares favourably with cryotherapy and argon laser photocoagulation. The retinal outcome and technique are discussed.

Fields, DVLC and panretinal photocoagulation

Laser panretinal photocoagulation (PRP) reduces visual loss in proliferative diabetic retinopathy but decreases peripheral retinal function. The Driver and Vehicle Licensing Centre (DVLC) states that when a patient volunteers that he or she has had photocoagulation, a questionnaire will then be sent to the patient's diabetic physician who can refer the patient for formal field testing. Of 30 patients who had PRP, 15 failed DVLC visual field regulations using the Esterman binocular field test on the Humphrey field analyser. The failures were more likely to have had treatment with a xenon laser, but there was no difference between the groups as regards age, number of burns or whether an argon or diode laser was used. The patients who failed were more likely to be hypertensive (p = 0.04). Two patients with unilateral PRP could not meet the driving regulations because of other field defects. Diabetes itself causes field defects, and therefore even with small amounts of laser, formal field testing may be necessary.

Comparison of photocoagulation with the argon, krypton, and diode laser indirect ophthalmoscopes in rabbit eyes

PURPOSE

The purpose of this study is to compare photocoagulation with the argon green, krypton red, and diode infrared laser indirect ophthalmoscopes in an experimental setting.

METHODS

Photocoagulation was performed with each of the laser indirect ophthalmoscopes in a grid pattern within one sector of the same eye of 14 Dutch-belted rabbits. Treatment was performed either with or without scleral depression. Measurements of the retinal burn diameters were performed after hemisecting the globes, and the burns were examined with light microscopy.

RESULTS

Variation in burn intensity and diameter (10% to 28%) was common with all 3 laser indirect ophthalmoscopes. Five times more output energy was required to make equivalent burns with the diode laser indirect ophthalmoscope than with the argon or krypton laser indirect ophthalmoscopes. Choriovitreal hemorrhages only occurred during scleral depression. Histopathologically, the argon green laser indirect ophthalmoscope burns spared the choroid and inner sclera, while the intense krypton and diode burns had full-thickness choroidal involvement and even thermal injury to the inner sclera. Scleral depression reduced the mean energy required to create equivalent burns with all three laser indirect ophthalmoscopes. There was a 10% to 40% reduction in the mean retinal burn diameter with scleral depression (argon green, P < 0.0005; krypton red, P < 0.0005; and diode, P < 0.025).

CONCLUSION

Photocoagulation with the argon green, krypton red, or diode infrared laser indirect ophthalmoscopes is a safe and effective method of retinal ablation. Decreasing the posterior nodal distance of the eye with scleral depression will produce a smaller spot on the retina with the laser indirect ophthalmoscope.