Changes in Macular Thickness After Patterns Scan Laser

The safety and scientific validity of this study is the responsibility of the study sponsor and investigators. Listing a study does not mean it has been evaluated by the U.S. Federal Government. Read our disclaimer for details. Identifier: NCT00563628
Recruitment Status : Unknown
Verified November 2007 by Asociación para Evitar la Ceguera en México.
Recruitment status was:  Recruiting
First Posted : November 26, 2007
Last Update Posted : November 26, 2007
Information provided by:
Asociación para Evitar la Ceguera en México

Brief Summary:
Laser photocoagulation has become the treatment of choice in PDR. Laser photocoagulation has become the treatment of choice in TMD. The aim is to destroy a substantial portion of the peripheral retina in order to reduce the angiogenic stimulus (decrease the difference between oxygen demand and the administration). Their effectiveness is determined by the extent of destruction of the retina (2.4).

Condition or disease Intervention/treatment Phase
Non Proliferative Diabetic Retinopathy. Proliferative Diabetic Retinopathy. Device: Panretinal photocoagulation with PASCAL system Phase 4

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Detailed Description:


The concept of retinal photocoagulation was introduced by Meyer-Schwickerath for treatment of diabetic retinopathy in the 50s (1, 6). The first successfully used laser was the arc xenon laser (polychromatic, inefficient, and hard to handle). Then the ruby and argon laser appeared (with mayor improvements in design and management). The modern era of photocoagulation as we know it began in the late 70s.

With these available technologies, the focal photocoagulation, the panretinal photocoagulation and the grid photocoagulation were developed. Witch proved effective for the treatment of severe non-proliferative diabetic retinopathy, proliferative diabetic retinopathy in different multicenter studies (ETDRS, DRS) (1.6).

Patients usually receive from 1200 to 1500 laser shots in 2 to 4 sessions lasting from 10 to 20 minutes, during 2 to 4 weeks. The procedure can be time consuming, tedious and painful.

Until now little has changed in the overall design of lasers of 30 years ago. The differences are the introduction of fibre optics and air-based cooling systems. These innovations do not have any impact on the way in which the treatment or the success.

Early efforts to improve photocoagulation included complex recognition systems and eye tracking to try to manage a fully automated process. That required a preview image of the retina. Attempts were also made to determine the appropriate dose of energy for getting the job done. The complexity of these systems prevented their clinical use (1).

The PASCAL is a system of semiautomatic pattern laser, which allows much faster processing, accuracy and control of treatment by a doctor at all times. The difference with the regular laser systems is that PASCAL manages a dual frequency Nd: YAG that works at a wavelength of 532nm, which is capable of firing a single shot from up to 56 shots in pre patterns (1x1, 2 x2, 3x3, 4x4, 5x5). By using time exposures of between 10 and 20 ms, you can make multiple shots at the same time that a shot with conventional laser is done (100 ms). These short pulses allow energy laser focus better in the tissues, produces less pain, Reduce the heat delivered to the choroid, and less diffusion of heat with the subsequent less damage to surrounding tissues (1).

The first study was published in the Retina 2006, by Blumenkanz, Palanker, Marcelino, et al. In which describe their use in rabbit's retinas. In which compared the effect of a number of pulses of different durations and powers. They applied exposition of 10, 20, 50 and 100 ms. The study found that at lower exposure time is required energy of 2 to 3 times more to produce the same effect, but the pulse had less energy. As they increased the exposure time, les power was needed, but the pulsed had also more energy. As the energy increased the shots was less homogeneous, less localized and changes in the final size (110-170micm) (1).

ERG: It reflects the activity of the retina in "mass". In studies of the effect of photocoagulation on the activity of the retina, it have typically been used the amplitude of them a and b wave as criteria of tissue destruction. But there is no consistency among the various studies that have already reported variations of 10 to 95% in the amplitude (especially in wave b) due to the variability in the length of effective ablation of the retina. Others suggest that a wave to be smaller than the b, showing an injury in the primary layer of photoreceptors. Others say that the decline was equal in both waves. But something we all conclude is that the response in the ERG is reduced more than expected based in the coagulated area. But when it is higher, the fall in the ERG is more than what was expected (60% of destruction = 80% decrease of ERG). An average photocoagulation destroys about 40% of the retina approximately (5).

The destruction of the peripheral retina decreases the ERG response, besides laser affect regions of adjacent tissue, causing deterioration in the transmission of signals from the photoreceptors in the proximal retina. What explains the previous reports of large decrease in amplitude on the basis of the area coagulated (2). The laser energy is absorbed by the RPE cells, and the adjacent layer of photoreceptors. What also produces external injury to the retina so you can also observe an increase in the implicit time (3).

A few years ago changing arc xenon to argon marked a difference in the amount of burned retina and decrease in the implicit time and amplitudes of the waves (5).

Macular Edema: Is recognized as a potential adverse effect of panretinal photocoagulation. Witch may transitory or permanent decrease the visual acuity of the patient. Approximately 60% of photocoagulated patients show an increase in the foveal thickness. Despite the fact that it has been said that a change of the self-distribution of blood flow is responsible for this increase in the thickness, today it is believed that these changes are due to post-laser inflammation. Despite that it is performed outside of the vascular arches; it is generally formed by those within.

The inflammation factors, in addition to the direct effect that is exercised on intracellular unions have shown themselves capable of producing a change in the barrier mediated leukocytes. These factors are produced in the peripheral region to the photocoagulated area. The laser stimulates the production of adhesion molecules in the area around the shot and in the non photocoagulated area, which produces bearings and recruitment of leukocytes, secondary accumulation in the posterior pole and subsequent alteration of the hemato-retinal barrier (7).

Study Type : Interventional  (Clinical Trial)
Estimated Enrollment : 8 participants
Allocation: Randomized
Intervention Model: Single Group Assignment
Masking: None (Open Label)
Primary Purpose: Treatment
Official Title: Pattern Scan Laser System vs Regular Photocoagulation System: Changes in Macular Edema Post Treatment.
Study Start Date : October 2007
Estimated Study Completion Date : February 2008

Resource links provided by the National Library of Medicine

U.S. FDA Resources

Intervention Details:
    Device: Panretinal photocoagulation with PASCAL system
    Use the PASCAL laser system to deliver a retina photocoagulation
    Other Name: Pattern Scan Laser system

Primary Outcome Measures :
  1. Retinal thickness after treatment [ Time Frame: 12 weeks ]

Information from the National Library of Medicine

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Ages Eligible for Study:   25 Years to 95 Years   (Adult, Senior)
Sexes Eligible for Study:   All
Accepts Healthy Volunteers:   No

Inclusion Criteria:

  • Patients older than 25 years, with a diagnosis of severe NPDR or PRD.
  • Good pupil mydriasis (minimum 5mm) With clear media
  • Patients without previous laser treatment or treatment with antiangiogenic drug.

Exclusion Criteria:

  • Patients who do not accept informed consent.
  • Patients with clinical macular Edema before treatment.
  • Significant corneal opacity.
  • Patients with other eye diseases that interfere with the studies required for the monitoring of patients.
  • History of refractive surgery, glaucoma or ocular hypertension, intraocular inflammation, choroiditis multifocal, retinal detachment, optic neuropathy (4).
  • Patients with tractional retinal detachment due to abundant fibrovascular tissue. Or important fibrovascular tissue that fold or detach the retina.

Information from the National Library of Medicine

To learn more about this study, you or your doctor may contact the study research staff using the contact information provided by the sponsor.

Please refer to this study by its identifier (NCT number): NCT00563628

Contact: Raul Velez-Montoya, MD 525510841400 ext 1171
Contact: Yoko Burgoa, Lic 525510841400 ext 1172

Asociaciòn para Evitar la Ceguera en Mèxico Recruiting
Mexico, DF, Mexico, 04030
Contact: Yoko Burgoa, Lic    525510841400 ext 1171   
Sponsors and Collaborators
Asociación para Evitar la Ceguera en México
Principal Investigator: Raul Velez-Montoya, MD Ascoiaciòn para Evitar la Ceguera en Mexico
Principal Investigator: Hugo Quiroz-Mercado, MD Asociaciòn para Evitar la Ceguera
Principal Investigator: Virgilio Morales-Canton, MD Asociaciòn para Evitar la Ceguera

Publications: Identifier: NCT00563628     History of Changes
Other Study ID Numbers: PASCAL001
First Posted: November 26, 2007    Key Record Dates
Last Update Posted: November 26, 2007
Last Verified: November 2007

Keywords provided by Asociación para Evitar la Ceguera en México:
Pattern Scan Laser.
Diabetic retinopathy treatment.
Laser treatment

Additional relevant MeSH terms:
Retinal Diseases
Diabetic Retinopathy
Eye Diseases
Diabetic Angiopathies
Vascular Diseases
Cardiovascular Diseases
Diabetes Complications
Diabetes Mellitus
Endocrine System Diseases