Chronic central serous chorioretinopathy (CSC) is a relatively frequent eye disease that often occurs in patients in the professionally active age range. In this disease, there is pooling of fluid under the central retina (the macula). This specific form of macular degeneration can cause permanent vision loss, image distortion, loss of color and contrast vision due to this fluid under the retina. An early diagnosis and treatment may improve the visual outcome and quality of life. To date there is no international consensus on the optimal treatment of chronic CSC. Many retrospective studies suggest that treatment with photodynamic therapy (PDT) is effective in chronic CSC. Micropulse laser (ML) therapy may also be effective in this disease.

The proposed study is the first prospective randomized controlled trial in chronic CSC. In this study, participants with chronic CSC will be randomized into two treatment groups, PDT or ML treatment. The trial is a superiority study, because retrospective studies suggest that PDT treatment may be more effective than ML treatment. Therefore, PDT treatment is challenged against ML treatment.

The null hypothesis of the study is that PDT treatment is more effective than ML treatment in patients with active chronic CSC. The alternative hypothesis is that PDT treatment is not more effective than ML treatment in these patients.

Treatment success will not only be based on anatomical improvement, but also on functional endpoints, which are most important from a patient's perspective.

The study will take place in five large tertiary referral university hospitals in Europe that have extensive experience with conducting clinical trials (in Nijmegen, the Netherlands; Cologne, Germany; Leiden, the Netherlands; Oxford, United Kingdom; and Paris, France). Each of these centers has confirmed sufficient funding to conduct the research. The study will last max. 8 months per participant. Each participant will come for 5 (in the case of 1 treatment) or 7 visits (in the case of 2 treatments). Study evaluations will be mostly part of regular clinical care. The whole study will last for max. 24 months.

PURPOSE AND DESIGN There is no international consensus on the optimal treatment protocol of chronic CSC. Nevertheless, photodynamic therapy (PDT) has emerged as the treatment of choice in many centres worldwide. PDT uses a photosensitive drug, verteporfin (Visudyne®), that is administered once intravenously before treatment with a specific type of laser. PDT treatment has been developed originally as treatment for another form of macular degeneration, age-related macular degeneration, on which there are extensive data available. There are several other retinal diseases for which PDT with verteporfin is successfully used as an off-label treatment. The use of PDT treatment in chronic CSC is based on the high rate of anatomic success, the increase of visual acuity, the improvement in retinal sensitivity, and an excellent safety profile reported in many retrospective studies. The PDT strategies that are generally used are either with half the dose of verteporfin (Visudyne®) and full fluence (energy) of laser treatment, half the fluence level and the full dose of verteporfin, or half the treatment time using the full dose of verteporfin and full fluence, as compared to the original protocol that was used for neovascular age-related macular degeneration. These PDT strategies that use either half-dose of half-fluence treatment have been developed because a combination of the dosage and fluence that was originally used for the treatment of neovascular age-related macular degeneration showed a higher risk of developing choroidal ischemia and retinal atrophic changes. The half-dose and half-fluence PDT strategies, however, have been shown to be safe and effective in relatively large retrospective studies and one non-controlled non-randomized prospective study by Chan et al. in chronic CSC patients with sufficient follow-up periods.

Therefore, tailoring the therapy to obtain the maximal treatment effect with minimal toxicity is essential in treating patients with CSC. By reducing the dose of verteporfin, studies have demonstrated that the potential retinal damage caused by PDT can be minimized while the photodynamic effects in inducing choroidal vasculature changes required for treating CSC remain sufficient. We have chosen for half-dose because this "safety-enhanced" protocol appeared to be one of the safest and effective treatment options in patients with active chronic CSC.

PDT will be compared with micropulse laser (ML) treatment as a control arm, and not with sham or conventional laser treatment, for a number of reasons. First, sham (no treatment) was studied by Chan et al. who showed a large difference in anatomic outcome (complete resolution of subretinal fluid) and functional outcome (visual acuity) between the half-dose PDT and placebo group in the acute form of CSC, which often resolves spontaneously after a few weeks in contrast to chronic CSC. As it is well-established that prolonged leakage of subretinal fluid under the macula due to chronic CSC may lead to permanent visual loss, it is not desirable to compare half-dose PDT treatment with sham. Apart from these ethical considerations to refrain from comparing with sham, adding a third sham study arm would require an extra amount of study patients that would complicate the recruitment process. The treatment of CSC with ML treatment has been shown to be effective and safe in retrospective studies in 41-58% of patients. The safety and efficacy of ML treatment has also been shown in various other retinal diseases. In contrast, it has been shown that conventional laser treatment of focal leakage point on fluorescein angiography in CSC does not result in a better visual outcome. Also, conventional laser treatment has a higher risk of complications then ML and PDT, including visual loss, scotoma, decreased color vision, decreased contrast sensitivity, and choroidal neovascularization.

The proposed study is a superiority study, as retrospective studies suggest that the rate of anatomical and functional success of half-dose PDT treatment might be higher than ML treatment. However, none of these previous studies on half-dose PDT and ML treatment were prospective, randomized, as well as controlled. Therefore, we have chosen to challenge the half-dose PDT treatment arm against a treatment arm of ML treatment.

The number of visits and examinations have been reduced to a minimum, and conform to standard clinical care as much as possible. Extra examinations include a more extensive visual acuity measurement, microperimetry, and a questionnaire. These extra examinations are required to evaluate the functional vision-related endpoints of the study. Care will be taken to plan all examinations on the same day as much as possible.

RECRUITMENT AND CONSENT Patients will be informed about the treatment options for their eye disease that are currently available. Study investigators will obtain consent for participation in the study, but consent for currently available treatments outside the study will be obtained by medical and nursing staff as would be done routinely. Written and verbal versions of the participant information and informed consent will be presented to the participants, detailing the exact nature of the study, the implications and constraints of the protocol, the known side effects, and any risks involved in taking part. It will be clearly stated that the participant is free to withdraw from the study at any time for any reason without prejudice to future care, and with no obligation to give the reason for withdrawal. Care will be taken to avoid coercion and undue influence of the "recruiter" on the potential participant.

The potential participant will be allowed as much time as wished to consider the information, and the opportunity to question the Investigator, their General Practitioner or other independent parties to decide whether they will participate in the study.

CONFIDENTIALITY The source documents and participants' Case Report Form (CRF) data will always remain in the study centre in which the patient is treated (either Oxford, Cologne, Paris, or Nijmegen). No person-identifiable information will be used unless it is absolutely necessary. The trial staff will ensure that the participants' anonymity is maintained. The participants will be identified only by initials and a participants identification number on the CRF and the electronic database. All documents will be stored securely and only accessible by trial staff and authorised personnel. The study will comply with the Data Protection Act which requires data to be anonymized as soon as it is practical to do so. Anonymized data will be entered into a purpose-built digital database that is maintained by a contract research organisation, the Clinical Research Centre Nijmegen (www.crcn.nl), which is affiliated with the coordinating academic centre, the Institute of Ophthalmology of the Radboud University Nijmegen Medical Centre in Nijmegen the Netherlands.

INCLUSION CRITERIA:

• male and female patients ≥ 18 years of age who are able to give written informed consent
• active chronic central serous chorioretinopathy
• subjective visual loss > 6 weeks, interpreted as onset of active disease
• subretinal fluid that includes the fovea on OCT scanning at Baseline Examination.

Please NOTE: Subretinal fluid does not have to include fovea on OCT to be eligible for treatment at Control Visit 1, as long as there is persistent subretinal fluid in the macula, which is interpreted as persistently active disease (see 5.7 "Retreatment criteria and considerations").

• hyperfluorescent areas on ICG angiography
• ≥1 ill-defined hyperfluorescent leakage areas on fluorescein angiography with retinal pigment epithelial window defect(s) that are compatible with chronic CSC

EXCLUSION CRITERIA:

The participant may not enter the study if ANY of the following apply:

• any previous treatments for active CSC in the study eye
• current treatment with corticosteroids (topical or systemic), or anticipated start of corticosteroid treatment within the first 7-8 months from the start of the trial period
• evidence of other diagnosis that can explain serous subretinal fluid or visual loss
• BCVA < 20/200 (Snellen equivalent)
• profound chorioretinal atrophy in central macular area on ophthalmoscopy and OCT
• myopia > 6 dioptres
• visual loss and/or serous detachment on OCT < 6 weeks
• continuous and/or progressive visual loss > 18 months or serous detachment on OCT > 18 months
• no hyperfluorescence on ICG angiography
• intraretinal edema on OCT
• (relative) contraindications for PDT treatment (pregnancy, porphyria, severely disturbed liver function). Pregnancy will not be routinely tested in female patients, but the possibility of pregnancy will be discussed during eligibility screening
• (relative) contraindications for fluorescein angiography or ICG angiography (known allergies especially against shellfish, previous reactions)
• Soft drusen in treated eye or fellow eye, signs of choroidal neovascularization on ophthalmoscopy and/or fluorescein angiography/indocyanine green angiography