THE MACULAR PHOTOCOAGULATION STUDY

Although photocoagulation was recognized as being potentially beneficial for the treatment of choroidal neovascularization in the 1970s, many questions remained. The results of the Macular Photocoagulation Study (MPS) in dozens of publications have provided ophthalmologists with invaluable information relating to the clear benefits of laser ablation of subretinal neovascular lesions, with respect to their location to the fovea in the underlying disease process. The MPS, moreover, examined the influence of laser wavelength on treatment benefit and helped ophthalmologists understand the prognostic value of specific fundus features.

Study Objectives

The MPS set out initially to examine the utility of laser photocoagulation to leaking subretinal new vessel growth outside the fovea in preventing significant loss of visual acuity. This question was addressed for eyes with neovascular age-related macular degeneration (AMD), neovascular ocular histoplasmosis syndrome (OHS), and neovascular idiopathic choroidal neovascular membranes. Subsequent reports examined the incidence and risk factors for neovascular membrane persistence or recurrence and evaluated the benefit of photocoagulation of persistent and recurrent choroidal neovascularization (CNV). The visual outcomes in eyes receiving photocoagulation of extrafoveal and juxtafoveal CNV were compared with untreated control eyes in each group (AMD, OHS, or idiopathic CNV). The treatment benefit for laser photocoagulation of new and recurrent subfoveal CNV was evaluated for AMD only. In addition, the influence of laser wavelength on treatment benefit and the interpretation and prognostic value of specific fundus features was evaluated.

Treatment Groups/Trial Design

The Extrafoveal Study

For inclusion in the extrafoveal study, the major eligibility criteria were as follows:

■angiographic evidence of a well-demarcated choroidal neovascular membrane 200 µm to 2500 µm from the center of the foveal avascular zone (FAZ);

■best-corrected visual acuity 20/100;

■symptoms attributable to the neovascular membrane;

■drusen in eyes eligible for the AMD arms;

■at least one characteristic “histo-spot” in eyes eligible for the OHS arm;

■the absence of atrophic scars, drusen, or other retinal findings that could account for the neovascular membrane in eyes eligible for the idiopathic arms;

■a minimum age of 18 years for the OHS and idiopathic arms; and

■a minimum age of 50 years at the time of randomization in the AMD arm.

Patients were excluded if they had a history of prior laser photocoagulation or coexisting ocular disease that may otherwise affect visual acuity.

The Juxtafoveal (Krypton) Study

Eligible eyes had the following characteristics:

■well-demarcated neovascular AMD, neovascular OHS, or idiopathic CNV;

■the edge of the CNV was 1 µm to 199 µm from the center of the FAZ;

■CNV greater than 200 µm from the FAZ with adjacent blood or pigment (blocked fluorescence) extending within 200 µm; and

■best corrected visual acuity 20/400.

Other inclusion criteria were identical to those of the extrafoveal studies.

The Subfoveal New CNV AMD Study

Eligible patients had a fluorescein angiogram obtained less than 96 hours before randomization that demonstrated CNV with well-demarcated boundaries showing new vessel growth underneath the center of the FAZ covering a total area less than 3.5 MPS standard disc areas and a visual acuity between 20/40 and 20/320.

The Subfoveal Recurrent CNV Study

Major eligibility criteria included the following:

■a fluorescein angiogram obtained less than 96 hours before randomization demonstrating either:

1.CNV under the center of the FAZ contiguous with a prior treatment scar or

2.CNV within 150 µm from the center of the FAZ contiguous with a scar that had expanded under the fovea;

■visual acuity at entrance of 20/40 to 20/320;

■following proposed laser photocoagulation, some portion of the retina within 1.5 mm from the center of the FAZ would remain untreated;

■the total area occupied by prior new treatment areas would be less than 6 MPS disc area;

■apart from the scar, the majority of the lesion was composed of CNV; and

■patients 50 years or older without other ocular disease potentially affecting visual acuity.

Eligible eyes of consenting patients were randomized to either laser treatment or no treatment. Eyes enrolled in the subfoveal studies that were randomized to laser photocoagulation were further randomized to treatment with argon green laser or krypton red laser photocoagulation.

Outcome Measures

The primary MPS outcome measure was “severe visual loss” defined as a loss of six or more lines of visual acuity as measured on the ETDRS chart. The subfoveal studies evaluated reading speed and contrast threshold as secondary outcome measures. The rates of recurrent and persistent CNV in treated eyes and the incidence of CNV in previously unaffected eyes were also recorded.

Summary of Results and Implications for Clinical Practice

Patient Monitoring and Examination

Patients at risk for developing CNV should be examined periodically to evaluate eligibility for treatment. These patients should monitor their central vision in each eye daily with alternate monocular cover tests. A symptomatic disturbance of reading vision, distance vision,

or Amsler grid testing should be followed by prompt examination to identify a treatable lesion at the earliest possible time.

Extrafoveal and Juxtafoveal Lesions (Tables 1 and 2)

The results of the MPS are particularly compelling and unambiguous for extrafoveal and juxtafoveal CNV lesions, including peripapillary and nasal macular lesions.

■For AMD, OHS, and idiopathic groups, laser-treated eyes lost less vision than untreated eyes.

■Although hypertensive AMD patients did not appear to benefit from laser treatment for juxtafoveal lesions, laser treatment is recommended for all eyes with extrafoveal and juxtafoveal CNV meeting eligibility criteria for AMD, OHS, and idiopathic studies.

■Retrobulbar or peribulbar anesthesia is recommended, but successful treatment can be accomplished with topical anesthesia in selected patients.

■Careful comparison of preand post-treatment photographs enhance efforts to apply complete and adequate coverage of the CNV complex.

■Because of high persistence and recurrence rates, the improved visual outcome in patients without recurrence, and the expected poor visual outcome following subfoveal extension of a previously extrafoveal or juxtafoveal lesion, close monitoring after treatment are recommended.

■Evaluation with fluorescein angiography at 2-week intervals after treatment is recommended.

Subfoveal Lesions (Tables 3 and 4)

Only eyes with AMD and subfoveal CNV lesion complexes received laser treatment in the subfoveal arm of the MPS.

■Laser treatment should be considered for neovascular lesions that meet eligibility criteria for the Subfoveal New CNV Study or the Subfoveal Recurrent CNV Study.

■Because there may be an initial drop in visual acuity (particularly in eyes with visual acuity better than 20/100 or lesions greater than 2 MPS disc areas), a frank discussion with the patient regarding the visual expectations and long-term treatment benefit is critical.

■Although data supporting the treatment of recurrences in eyes previously treated for subfoveal CNV are lacking, close follow-up is recommended to limit the size of the laser scar should persistence or recurrence be detected and treated.