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   Table of Contents      
OPHTHALMOLOGY PRACTICE
Year : 1997  |  Volume : 45  |  Issue : 2  |  Page : 125-128

Laser photocoagulation in retinal vein occlusion : Branch vein occlusion study and central vein occlusion study recommendations


Anheuser-Busch Eye Institute, St. Louis University School of Medicine, Missouri, USA

Correspondence Address:
S Saxena
Anheuser-Busch Eye Institute, St. Louis University School of Medicine, Missouri
USA
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Source of Support: None, Conflict of Interest: None


PMID: 9475033

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How to cite this article:
Saxena S. Laser photocoagulation in retinal vein occlusion : Branch vein occlusion study and central vein occlusion study recommendations. Indian J Ophthalmol 1997;45:125-8

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Saxena S. Laser photocoagulation in retinal vein occlusion : Branch vein occlusion study and central vein occlusion study recommendations. Indian J Ophthalmol [serial online] 1997 [cited 2019 Oct 16];45:125-8. Available from: http://www.ijo.in/text.asp?1997/45/2/125/15003



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Venous occlusive diseases are among the most common retinal diseases seen in clinical practice. Increasing use of photocoagulation therapy along with fluorescein angiography has aided recognition of the disease, study the nature and course of the disease and culminate into small clinical trials. Consequently, it became evident that prospective, randomized, controlled, clinical trials were required to answer questions about treatment efficacy. Branch Vein Occlusion Study (BVOS) and Central Vein Occlusion Study (CVOS) have outlined the management strategies. These studies have been summarized below.


  Branch vein occlusion study Top


Branch Vein Occlusion Study [1, 2] was a multi-centre, prospective, randomized, controlled clinical trial supported by the National Eye Institute, Bethesda, Md.


  Objectives Top


The BVOS was designed to answer the following questions about branch retinal vein occlusion (BRVO):



  1. 1. Can peripheral scatter argon laser photocoagulation prevent the development of neovascularization ?


  2. 2. Can peripheral scatter argon laser photocoagulation prevent vitreous haemorrhage ?


  3. 3. Can macular argon laser photocoagulation improve visual acuity in eyes with macular oedema reducing vision to 6/12 or worse ?





  Protocol Top


Patients seen in six clinics with signs of BRVO were considered for the study. Patient eligibility criteria are summarized in [Table - 1].

Eyes in groups I and II were randomized either to "scatter" laser photocoagulation or no laser treatment. The patients were followed-up to answer questions 1 and 2 respectively. Recruitment of group X eyes only begun after the minimal sample size required for group I had been reached and so further recruitment terminated. Patients in group X were recruited to maintain a pool of cases that would have a high risk of developing neovascularization and therefore become eligible for group II. Group X patients were also followed up for natural history information. Group III eyes were randomized either to a "grid" pattern of photocoagulation within the involved macular region or to no laser treatment. The information was used to answer question 3.

Photocoagulation was performed with argon laser. For groups I and II, scatter photocoagulation was performed. Laser spots were spaced one burn width apart, covering entire involved segment and extending no closer than 2 D D from the centre of the fovea. For group III, grid pattern of photocoagulation was performed over the area of capillary leakage, extending no closer than the edge of foveal avascular zone and not extending peripheral to major vascular arcade. Treatment in the papillomacular bundle was not prohibited in the protocol.[3] Laser characteristics for peripheral-scatter and macular grid are shown in [Table - 2]. Patients were followed up at regular interval. Stereoscopic colour fundus photographs and fundus fluorescein angiograms were evaluated.


  Results and Recommendations Top


BVOS[2] results showed that peripheral scatter argon laser photocoagulation could prevent the development of both neovascularization and vitreous haemorrhage to a significant degree. The data accumulated in this study suggested that peripheral scatter treatment should be applied after, rather than before, the development of neovascularization. The study group recommended laser photocoagulation for patients with BRVO who have developed neovascularization and who meet the eligibility criteria. BVOS[1] demonstrated that argon laser photocoagulation improved the visual outcome to a significant degree in eyes with BRVO and visual acuity reduced from macular oedema to 6/12 or worse. The study group recommended laser photocoagulation for patient with macular oedema associated with BRVO who meet the eligibility criteria. Algorithms for management of BRVO is presented in [Figure - 1] and [Figure - 2].


  Central vein occlusion study Top


The Central Vein Occlusion Study[4][5][6][7][8] (CVOS) is a multicentre, prospective, randomized, controlled clinical trial supported by the National Eye Institute, Bethesda, Md.


  Objectives Top


The CVOS was designed to answer the following questions about central retinal vein occlusion (CRVO):



  1. 1. Does early panretinal photocoagulation (PRP) prevent iris neovascularization (INV) in eyes with ischaemic CRVO?


  2. 2. Does macular grid-pattern laser photocoagulation improve visual acuity in eyes with reduced vision due to macular oedema from CRVO?


  3. 3. What is the natural history of eyes with CRVO that have little or no evidence of ischaemia (less than 10 disc areas of non-perfusion)?


  4. 4. Is early PRP more effective than PRP at first identification of INV in preventing further ocular morbidity due to progressive neovascular glaucoma in eyes with ischaemic CRVO ?





  Protocol Top


Patients seen in nine clinics with signs of CRVO were considered for the study. Patients with CRVO were divided into 4 study groups on the basis of the perfusion status of the retina and presence of decreased vision associated with macular oedema: perfused, nonperfused, indeterminate and macular oedema. Patient eligibility criteria are summarized in [Table - 3].

Random treatment assignments in groups N and M were made using computer-generated random allocation. Group N eyes were stratified by clinic and group M eyes by both clinic and duration of the CRVO (less than 1 year or greater than or equal to 1 year). Both eyes of the patient could be considered for the study only if they were eligible simultaneously. If both eyes of the patient were eligible for a randomized group, one eye was randomly assigned to panretinal photocoagulation treatment and the other to observation. On the assumption that the need to evaluate grid-pattern treatment for macular oedema is independent of the treatment status of the periphery of the eye, the protocol allowed eyes in other CVOS groups to be entered into group M as well. Group P eyes were entered into group I or N and closed out of group P if sufficiently increased retinal haemorrhage and / or retinal capillary nonperfusion occurred and the eye met the eligibility criteria of the new group.

Grid-pattern of laser photocoagulation covered only the area of leaking capillaries. Treatment covered all of the areas of leaking capillaries within 2 disc diameters of the centre of the fovea; could not extend beyond 2 disc diameters from the fovea and could not extend within the foveal avascular zone. Treatment avoided collateral vessels and retinal haemorrhages 100 m spots at 0.1 second, to produce medium white burn, with a spacing of about one half to one burn-width apart were used.

Panretinal photocoagulation treatment was evenly spaced to or beyond the equator in all quadrants, no closer than 2 disc diameters from the centre of the fovea and no closer than 500 m nasal to the disc. Laser spots were spaced one half to one burn-width apart. Laser characteristics for panretinal photocoagulation are shown in [Table - 4].

Patients in the CVOS were followed up at regular intervals for 3 years. Colour fundus photographs and fundus fluorescein angiography were done at baseline and at regular intervals. Standard photographic views were employed. Slit lamp examination, gonioscopy and slit lamp photography were also performed as per the manual of operations for central retinal vein occlusion study.[6]

[TAG:2]Results and Recommendations

Baseline and early natural history report[4]:

(a) Four month natural history for eyes in group P:[/TAG:2]

Sixteen percent eyes demonstrated at least 10 disc areas of nonperfusion and / or INV and / or angle neovascularization (ANV) or were transferred to group I at or before the 4-month visit. Twenty two percent of these eyes showed INV and / or ANV and required panretinal photocoagulation. Eyes with duration of CRVO of less than one month were at a greater risk than eyes with a longer duration.


  (b) Complete natural history for eyes in group I: Top


Eight percent of the eyes developed INV and / or ANV in less than 1 month after study entry and 58% eyes were eligible for transfer or had developed INV and / or ANV by the 2-month visit.

These findings confirm the importance of follow-up examinations in the management of all patients with recent onset of CRVO.

[TAG:2]CVOS group M report[7][/TAG:2]

Macular grid laser photocoagulation had no effect on visual acuity in either patients with CRVO of recent onset (< 1 year) or in occlusions of longer duration, during the follow-up period. However, treatment clearly reduced angiographic evidence of macular edema. The results of this study do not support a recommendation for macular grid photocoagulation for the population meeting the CVOS group eligibility criteria.

[TAG:2]CVOS group N report[8][/TAG:2]

Four factors associated with the development of anterior segment neovascularization were identified: (1) extensive retinal capillary nonperfusion on fluorescein angiography; (2) large amounts of retinal haemorrhage; (3) short duration of CRVO and (4) male sex. The strongest predictor of 2 clock hours of iris neovascularization or angle neovascularization (TC-INV/ANV) was the extent of nonperfusion. Eyes with less than 30 disc diameters of nonperfusion and no other risk factor were at low risk, whereas eyes with 75 disc diameters or more (ie, eyes that show virtually no intact capillaries in the posterior pole) are at the highest risk. Prophylactic PRP does not totally prevent TC-INV/ANV and prompt regression of TC-INV/ANV in response to PRP is more likely to occur in eyes that have not been treated previously. The study group recommended careful observation with frequent follow-up examinations in the early months (including undilated slit lamp examination of the iris and gonioscopy) and prompt PRP of eyes in which TC-INV/ANV develops. Specific recommendations of CVOS are summarized in [Table - 5]. Algorithm for management of CRVO is shown in [Figure - 3].

 
  References Top

1.
The Branch Vein Occlusion Study Group: Argon laser photocoagulation for macula edema in branch vein occlusion. Am J Ophthalmol. 98:271-282, 1984.  Back to cited text no. 1
    
2.
The Branch Vein Occlusion Study Group: Argon laser scatter photocoagulation for prevention of neovascularization and vitreous hemorrhage in branch vein occlusion. Arch Ophthalmol. 104:34-41, 1986.  Back to cited text no. 2
    
3.
The Branch Vein Occlusion Study Group: Argon laser photocoagulation for macula edema in branch vein occlusion. Am J Ophthalmol. 99:218-219, 1985.  Back to cited text no. 3
    
4.
The Central Vein Occlusion Study Group: Baseline and early natural history report. Arch Ophthalmol. 111:1087-1095, 1993.  Back to cited text no. 4
    
5.
The Central Vein Occlusion Study Group: Central vein occlusion study of photocoagulation therapy. Baseline findings. Online J Curr Clin Trials. 1993 Oct 14; Doc No. 95.  Back to cited text no. 5
    
6.
The Central Vein Occlusion Study Group: Central vein occlusion study of photo-coagulation. Manual of operations. Online J Curr Clin Trials. 1993 Oct 2; Doc No. 92  Back to cited text no. 6
    
7.
The Central Vein Occlusion Study Group: Evaluation of grid pattern photocoagulation for macular edema in central vein occlusion. Ophthalmology. 102:1425-1433, 1995.  Back to cited text no. 7
    
8.
The Central Vein Occlusion Study Group: A randomized clinical trial of early panretinal photocoagulation for ischemic central vein occlusion. Ophthalmology. 102:1434-1444, 1995.  Back to cited text no. 8
    


    Figures

  [Figure - 1], [Figure - 2], [Figure - 3]
 
 
    Tables

  [Table - 1], [Table - 2], [Table - 3], [Table - 4], [Table - 5]



 

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