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Surgical Technique | Surgeon's Corner

Utility of Large Spot Binocular Indirect Laser Delivery for Peripheral Photocoagulation Therapy in Children FREE

Saranya C. Balasubramaniam, BA; Brian G. Mohney, MD; Genie M. Bang, MD; Thomas P. Link, BA; Jose S. Pulido, MD, MS, MPH, MBA
[+] Author Affiliations

Author Affiliations: Department of Ophthalmology, Mayo Clinic and Mayo Foundation, Rochester, Minnesota.


Arch Ophthalmol. 2012;130(9):1213-1217. doi:10.1001/archophthalmol.2012.1978.
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Published online

The purpose of this article is to demonstrate the utility of the large spot size (LSS) setting using a binocular laser indirect delivery system for peripheral ablation in children. One patient with bilateral retinopathy of prematurity received photocoagulation with standard spot size burns placed adjacently to LSS burns. Using a pixel analysis program called Image J on the Retcam picture, the areas of each retinal spot size were determined in units of pixels, giving a standard spot range of 805 to 1294 pixels and LSS range of 1699 to 2311 pixels. Additionally, fluence was calculated using theoretical retinal areas produced by each spot size: the standard spot setting was 462 mJ/mm2 and the LSS setting was 104 mJ/mm2. For eyes with retinopathy of prematurity, our study shows that LSS laser indirect delivery halves the number of spots required for treatment and reduces fluence by almost one-quarter, producing more uniform spots.

Figures in this Article

Laser photocoagulation using an indirect laser delivery system has made it possible to treat a number of retinal diseases in children including retinopathy of prematurity (ROP), Coats disease, pars planitis, intraocular tumors, and proliferative retinopathies.19 In pediatric patients requiring treatment under anesthesia, the laser indirect ophthalmoscopy (LIO) delivery system is widely used for its ease and tolerability. It was first developed by Mizuno and Takaku in 1981, who attached an indirect ophthalmoscope to a laser delivery system using a fiberoptic cable.1012 Lenses used with this method condense light from a light source to illuminate the fundus and create an aerial image that can be viewed through the binocular device. The advantages of the LIO method include increased access to the retinal periphery and increased field of view of the retina as well as the ability to treat patients in a supine position.13

Two laser therapies widely used with the LIO delivery method for treatment of retinal periphery are transpupillary thermotherapy and photocoagulation therapy. The goal of transpupillary thermotherapy is to create and maintain hyperthermia with a mild rise in temperature that is not high enough for the development of coagulation.1416 Mainster and Reichel15 calculated this rise to be between 4°C and 10°C using biophysical models and report hyperexpression of the heat shock protein HSP70, leading to cellular injury and apoptosis.15 In transpupillary thermotherapy, the diode laser (810 nm, infrared) is absorbed mainly by retinal pigment epithelium melanin as well as choroidal melanocytes to create a therapeutic effect.1416 In contrast, photocoagulation, also referred to as laser ablation, relies on raising retinal temperatures high enough to produce coagulation of the target tissue.17,18 Wavelengths of light used can range from 500 nm to 810 nm, depending on the retinal pigments being targeted. In photocoagulation, a more significant temperature rise occurs, with retinal tissues reaching temperatures between 45°C and 65°C.13

For transpupillary thermotherapy, a large spot size (LSS) setting is used, while in photocoagulation therapy, a standard spot size is most often used. The use of LSS photocoagulation therapy using LIO is not well documented in the literature. Recently, Shah and colleagues19 compared the use of continuous-mode LSS diode therapy with standard spot size conventional pulsed-mode diode therapy for patients with ROP. They found that LSS photocoagulation was 40% more time efficient than conventional laser spot size. They also found that there was no difference in complication rates or outcomes when using LSS. However, this study used continuous-mode LSS therapy and was limited to patients with ROP.

One of us (J.S.P.) has used LSS laser photocoagulation of the peripheral retina since 2010. We now present the use of LSS peripheral laser photocoagulation on 7 eyes of pediatric patients with a broad spectrum of diseases including Coats disease, pars planitis, ROP, and vasculitis with peripheral neovascularization. The goal of this article is to show the magnitude of increase in retinal spot area as well as the increased uniformity achieved when using LSS for peripheral laser photocoagulation. We also report 7 eyes for which standard spot sized peripheral ablation was used to show the reduction in the number of laser spots necessary to treat when using LSS LIO as compared with the small spot size setting.

All patients were evaluated and treated in the Department of Ophthalmology at the Mayo Clinic, Rochester, Minnesota. Institutional review board approval for retrospective review was obtained as study number 11-006584. Visual acuity was determined using the Snellen eye chart in a formal examination with patients old enough to participate. As described in Table 1, patients 1 through 4 were treated with LSS peripheral photocoagulation. Patient 1 was treated for unilateral Coats disease; patient 2, for bilateral vasculitis with peripheral neovascularization; and patient 3, for bilateral pars planitis.

Table Graphic Jump LocationTable 1. Data of Eyes Treated With Large Spot Size Laser Diode Photocoagulation

Patient 4 is a baby with bilateral prethreshold ROP for whom we used LSS in conjunction with the standard spot size to photographically document the relative size difference between the 2 spot sizes. For this patient, photograph documentation was performed by the Retcam (Clarity Medical Systems Inc) and can be seen in Figure 1.

Place holder to copy figure label and caption
Graphic Jump Location

Figure 1. Retcam (Clarity Medical Systems) photograph of adjacent spot size treatment delivered to patient 4. Large spot size photocoagulation spots (left) appear to be more uniform in shape and size than those delivered with the standard spot size setting (right).

For the 7 eyes treated from patients 1 through 4, peripheral photocoagulation was delivered using the LSS LIO (Iridex Corp) and an infrared diode laser of 810 nm (Oculight Slx; Iridex Corp) and either a 20-diopter (D) or 30-D lens (Volk Optical Inc). Laser therapy was delivered with continued observation through the lens while patients were under anesthesia and the LSS was aimed through a dilated pupil. The power and duration were adjusted to achieve white spot photocoagulation. For patients 5 through 8, similar methods and materials were used, except standard spot size setting photocoagulation was used (Table 2). Additionally, for patient 8, alternating therapy with the 20-D and the 30-D lens was used.

Table Graphic Jump LocationTable 2. Eyes Treated With Standard Spot Size Laser Diode Photocoagulation

When using LIO to deliver laser therapy, the 2 ways that treatment can be modified to produce the largest retinal spot size possible are by increasing the power of the condensing lens and using the larger spot size setting. A third, and less precise, way of increasing spot size is to defocus toward the patient. This can be inferred from the fact that the calculation of the true size of a spot on the fundus depends on the refraction, corneal curvatures, axial length, and magnification of the imaging system.13

The Iridex LIO system can deliver 2 spot sizes with a 20-D lens: the small spot size is 350 μm and the LSS is 1400 μm.20 When using a 30-D lens, the retinal spot size will increase by three-halfs, or ×1.5, given the following relationship13

Thus, assuming emmetropia and the average refractive power of the lens being 60 D, the 30-D condensing lens will produce a small spot size of 525 μm and LSS of 2100 μm.

The second way to increase the retinal spot size is by using the LSS setting, which we used in the 7 eyes of patients 1 through 4. To describe the potential efficacy of using the LSS setting, it is important to understand the differences in the area produced by each size setting. Mathematically, the theoretical area of the LSS as compared with the area of the small spot size is compared in the following equation. Assuming use of a 30-D lens with large spot diameter of 2100 μm and small spot diameter of 525 μm, the theoretical area of the spot delivered can be calculated:

Thus, for the Iridex LIO delivery system, one can achieve an area that is 16 times bigger when using the LSS with either a 20-D or a 30-D lens. In other words, 16 standard spots would be required to cover the area of 1 large spot. These calculations can be repeated to understand the magnitude of difference for the LIO delivery system in use.

To determine the actual difference in spot size, patient 4 (baby with ROP) was treated with the standard spot size LIO and adjacent LSS LIO, both performed with a 30-D lens (Figure 1). Treatment time was adjusted to obtain similar white spot photocoagulation. Using Image J (National Institutes of Health), each standard spot area was measured in units of pixels and compared to understand the objective difference in spot variability and area. Threshold settings were set to 164 with the watershed application. The areas were reported for 6 small spots (spot labels 2, 3, 4, 6, 7, and 14) as well as for 3 large spots (spot labels 10, 13, and 16) as summarized in Figure 2 and Table 3.

Place holder to copy figure label and caption
Graphic Jump Location

Figure 2. Image J (National Institutes of Health) analysis of Figure 1 can quantify the difference in pixel area of large spot size photocoagulation spots (1669-2311 pixels) and standard photocoagulation spots (805-1294 pixels), as listed in Table 3.

Table Graphic Jump LocationTable 3. Area in Pixels Produced by Image J Adjacent Spot Size Treatment Delivered to Patient 4a

In the eye of patient 4, which had adjacent spots treated with the standard spot size and LSS spot size, quantification of the respective areas was carried out using Image J. The median area for standard spot was 1020.5. The resulting range in pixel area for standard spot size was 805 to 1294 pixels and range for LSS was 1669 to 2311 pixels (Figure 2 and Table 3).

The Retcam photograph (Figure 1) also depicts increased uniformity in the large spots delivered and the standard spots appear to have marked variability in size and shape. This may be attributed, at least in part, to the reduced fluence achieved by using the LSS LIO. Using the power and time settings from patient 4 who received adjacent standard spot and LSS LIO, fluence was calculated using the theoretical radii of the spot sizes when using the 30-D lens. For the standard spot size of 525 μm, calculations were made based on the diameter of 0.525 mm, making the radius equal to 0.2625 mm. For the LSS of 2100 μm, calculations were based on the diameter of 2.100 mm, making the radius 1.050 mm. 

Thus, the theoretical fluence for LSS is reduced by almost one-quarter when compared with the fluence of standard spot size use.

We report increased uniformity in spots delivered by LSS LIO, which may be attributed to the reduced fluence delivered to the retina allowing for more controlled delivery of photocoagulation therapy. We propose that the high fluence delivered to the retina by the standard spot size setting creates a variable effect that can lead to the marked variability observed in the shape and uniformity of the spots delivered. Additionally, the high fluence needed with the standard spot size accounts for the variability of adjacent spots that are “too hot” and break the Bruch membrane next to spots that are barely visible.

For ROP, where peripheral diode photocoagulation is the mainstay of treatment, our data show significant reductions in the number of spots that must be delivered to treat bilateral disease. Patient 4 from the LSS treatment group can be compared with patient 6 and patient 8 from the standard spot size treatment group. All 3 patients had a diagnosis of bilateral prethreshold ROP, categorized as zone 2, stage 2/3 with plus disease. For patient 4, who received treatment with the LSS setting, 820 spots were delivered to treat both eyes. This can be compared with treatment received with the standard spot size setting in patient 6, who required 1621 spots, and patient 8, who required 2217 spots to treat bilateral disease. Thus, standard spot size peripheral laser photocoagulation requires more time, as supported by Shah and colleagues.19 Thus, for children requiring broad areas of photocoagulation under anesthesia, the LSS setting can reduce time under anesthesia and time spent delivering treatment.

The limitations of this study are that it is retrospective with a small sample size. Additionally, a randomized controlled trial is needed in which time to achieve LSS ablation is compared with time spent administering small spot size ablation. There is a paucity of literature on the efficacy of using LSS in peripheral laser photocoagulation, but the safety and long-term outcomes are assumed to be equivalent to using the standard small spot size.

Standard spot size is ideal for focal areas of treatment; however, for large treatment areas, the LSS setting shows promise. This article demonstrates the magnitude of increase in retinal spot area achieved when using LSS for peripheral laser ablation. Given the theoretical increase in retinal area achieved with LSS combined with the 30-D condensing lens, we report a reduced number of spots required to deliver treatment, as well as the ability to deliver spots with increased uniformity and reduced fluence. We conclude that the LSS setting is an improved technique that should be more widely used when performing peripheral laser photocoagulation in pediatric patients and adults requiring LIO photocoagulation, such as elderly or cognitively impaired individuals.

Correspondence: Jose S. Pulido, MD, MS, MPH, MBA, Mayo Clinic, Department of Ophthalmology, 200 First St SW, Rochester, MN 55905 (pulido.jose@mayo.edu).

Submitted for Publication: October 30, 2011; final revision received April 27, 2012; accepted May 2, 2012.

Financial Disclosure: None reported.

Funding/Support: This research was supported in part by an unrestricted grant from Research to Prevent Blindness Inc and a grant from the Paul Family.

Additional Contributions: We thank Joshua Boesche, BS, from the Division of Engineering, Mayo Clinic, Rochester, Minnesota, for guidance on performing image analysis using Image J.

Schefler AC, Berrocal AM, Murray TG. Advanced Coats' disease: management with repetitive aggressive laser ablation therapy.  Retina. 2008;28(3):(suppl)  S38-S41
PubMed   |  Link to Article
Couvillion SS, Margolis R, Mavrofjides E, Hess D, Murray TG. Laser treatment of Coats' disease.  J Pediatr Ophthalmol Strabismus. 2005;42(6):367-368
PubMed
Shapiro MJ, Chow CC, Karth PA, Kiernan DF, Blair MP. Effects of green diode laser in the treatment of pediatric Coats disease.  Am J Ophthalmol. 2011;151(4):725-731
PubMed
Nucci P, Bandello F, Serafino M, Wilson ME. Selective photocoagulation in Coats' disease: ten-year follow-up.  Eur J Ophthalmol. 2002;12(6):501-505
PubMed
Pulido JS, Mieler WF, Walton D,  et al.  Results of peripheral laser photocoagulation in pars planitis.  Trans Am Ophthalmol Soc. 1998;96:127-137, discussion 137-141
PubMed
Early Treatment for Retinopathy of Prematurity Cooperative Group.  Revised indications for the treatment of retinopathy of prematurity: results of the Early Treatment for Retinopathy of Prematurity randomized trial.  Arch Ophthalmol. 2003;121(12):1684-1694
PubMed
Goggin M, O’Keefe M. Diode laser for retinopathy of prematurity: early outcome.  Br J Ophthalmol. 1993;77(9):559-562
PubMed
Ling CS, Fleck BW, Wright E, Anderson C, Laing I. Diode laser treatment for retinopathy of prematurity: structural and functional outcome.  Br J Ophthalmol. 1995;79(7):637-641
PubMed
Paysse EA, Hussein MA, Miller AM, Brady McCreery KM, Coats DK. Pulsed mode versus near-continuous mode delivery of diode laser photocoagulation for high-risk retinopathy of prematurity.  J AAPOS. 2007;11(4):388-392
PubMed
Mizuno K. Binocular indirect argon laser photocoagulator.  Br J Ophthalmol. 1981;65(6):425-428
PubMed
Mizuno K, Takaku Y. Dual delivery system for argon laser photocoagulation: improved techniques of the binocular indirect argon laser photocoagulator.  Arch Ophthalmol. 1983;101(4):648-652
PubMed
Friberg TR. Clinical experience with a binocular indirect ophthalmoscope laser delivery system.  Retina. 1987;7(1):28-31
PubMed
Pulido JS, Folk JC. Laser Photocoagulation of the Retina and Choroid. San Francisco, CA: AAO; 2003
Oosterhuis JA, Journée-de Korver HG, Kakebeeke-Kemme HM, Bleeker JC. Transpupillary thermotherapy in choroidal melanomas.  Arch Ophthalmol. 1995;113(3):315-321
PubMed
Mainster MA, Reichel E. Transpupillary thermotherapy for age-related macular degeneration: long-pulse photocoagulation, apoptosis, and heat shock proteins.  Ophthalmic Surg Lasers. 2000;31(5):359-373
PubMed
Reichel E, Berrocal AM, Ip M,  et al.  Transpupillary thermotherapy of occult subfoveal choroidal neovascularization in patients with age-related macular degeneration.  Ophthalmology. 1999;106(10):1908-1914
PubMed
Vogel A, Birngruber R. Temperature profiles in human retina and choroid during laser coagulation with different wavelengths ranging from 514-810 nm.  Lasers Light Ophthalmol. 1992;5:9-16
Puliafito CA, Deutsch TF, Boll J, To K. Semiconductor laser endophotocoagulation of the retina.  Arch Ophthalmol. 1987;105(3):424-427
PubMed
Shah PK, Narendran V, Kalpana N. Large spot transpupillary thermotherapy: a quicker laser for treatment of high risk prethreshold retinopathy of prematurity. a randomized study.  Indian J Ophthalmol. 2011;59(2):155-158
PubMed
 Iridex Manual of Products. Mountain View, CA: Iridex Corp; 2011

Figures

Place holder to copy figure label and caption
Graphic Jump Location

Figure 1. Retcam (Clarity Medical Systems) photograph of adjacent spot size treatment delivered to patient 4. Large spot size photocoagulation spots (left) appear to be more uniform in shape and size than those delivered with the standard spot size setting (right).

Place holder to copy figure label and caption
Graphic Jump Location

Figure 2. Image J (National Institutes of Health) analysis of Figure 1 can quantify the difference in pixel area of large spot size photocoagulation spots (1669-2311 pixels) and standard photocoagulation spots (805-1294 pixels), as listed in Table 3.

Tables

Table Graphic Jump LocationTable 1. Data of Eyes Treated With Large Spot Size Laser Diode Photocoagulation
Table Graphic Jump LocationTable 2. Eyes Treated With Standard Spot Size Laser Diode Photocoagulation
Table Graphic Jump LocationTable 3. Area in Pixels Produced by Image J Adjacent Spot Size Treatment Delivered to Patient 4a

References

Schefler AC, Berrocal AM, Murray TG. Advanced Coats' disease: management with repetitive aggressive laser ablation therapy.  Retina. 2008;28(3):(suppl)  S38-S41
PubMed   |  Link to Article
Couvillion SS, Margolis R, Mavrofjides E, Hess D, Murray TG. Laser treatment of Coats' disease.  J Pediatr Ophthalmol Strabismus. 2005;42(6):367-368
PubMed
Shapiro MJ, Chow CC, Karth PA, Kiernan DF, Blair MP. Effects of green diode laser in the treatment of pediatric Coats disease.  Am J Ophthalmol. 2011;151(4):725-731
PubMed
Nucci P, Bandello F, Serafino M, Wilson ME. Selective photocoagulation in Coats' disease: ten-year follow-up.  Eur J Ophthalmol. 2002;12(6):501-505
PubMed
Pulido JS, Mieler WF, Walton D,  et al.  Results of peripheral laser photocoagulation in pars planitis.  Trans Am Ophthalmol Soc. 1998;96:127-137, discussion 137-141
PubMed
Early Treatment for Retinopathy of Prematurity Cooperative Group.  Revised indications for the treatment of retinopathy of prematurity: results of the Early Treatment for Retinopathy of Prematurity randomized trial.  Arch Ophthalmol. 2003;121(12):1684-1694
PubMed
Goggin M, O’Keefe M. Diode laser for retinopathy of prematurity: early outcome.  Br J Ophthalmol. 1993;77(9):559-562
PubMed
Ling CS, Fleck BW, Wright E, Anderson C, Laing I. Diode laser treatment for retinopathy of prematurity: structural and functional outcome.  Br J Ophthalmol. 1995;79(7):637-641
PubMed
Paysse EA, Hussein MA, Miller AM, Brady McCreery KM, Coats DK. Pulsed mode versus near-continuous mode delivery of diode laser photocoagulation for high-risk retinopathy of prematurity.  J AAPOS. 2007;11(4):388-392
PubMed
Mizuno K. Binocular indirect argon laser photocoagulator.  Br J Ophthalmol. 1981;65(6):425-428
PubMed
Mizuno K, Takaku Y. Dual delivery system for argon laser photocoagulation: improved techniques of the binocular indirect argon laser photocoagulator.  Arch Ophthalmol. 1983;101(4):648-652
PubMed
Friberg TR. Clinical experience with a binocular indirect ophthalmoscope laser delivery system.  Retina. 1987;7(1):28-31
PubMed
Pulido JS, Folk JC. Laser Photocoagulation of the Retina and Choroid. San Francisco, CA: AAO; 2003
Oosterhuis JA, Journée-de Korver HG, Kakebeeke-Kemme HM, Bleeker JC. Transpupillary thermotherapy in choroidal melanomas.  Arch Ophthalmol. 1995;113(3):315-321
PubMed
Mainster MA, Reichel E. Transpupillary thermotherapy for age-related macular degeneration: long-pulse photocoagulation, apoptosis, and heat shock proteins.  Ophthalmic Surg Lasers. 2000;31(5):359-373
PubMed
Reichel E, Berrocal AM, Ip M,  et al.  Transpupillary thermotherapy of occult subfoveal choroidal neovascularization in patients with age-related macular degeneration.  Ophthalmology. 1999;106(10):1908-1914
PubMed
Vogel A, Birngruber R. Temperature profiles in human retina and choroid during laser coagulation with different wavelengths ranging from 514-810 nm.  Lasers Light Ophthalmol. 1992;5:9-16
Puliafito CA, Deutsch TF, Boll J, To K. Semiconductor laser endophotocoagulation of the retina.  Arch Ophthalmol. 1987;105(3):424-427
PubMed
Shah PK, Narendran V, Kalpana N. Large spot transpupillary thermotherapy: a quicker laser for treatment of high risk prethreshold retinopathy of prematurity. a randomized study.  Indian J Ophthalmol. 2011;59(2):155-158
PubMed
 Iridex Manual of Products. Mountain View, CA: Iridex Corp; 2011

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