Discussion
Coats disease is a disease that is associated with retinal exudation, and telangiectatic and aneurysmal retinal vessels [
1,
2]. Coats disease can be diagnosed in infancy, late childhood or adolescence, and adulthood [
2,
5]. Both of our patients were male, with symptoms first presenting later in adolescence (case 1) and adulthood (case 2).
No etiology has been established and no systemic conditions are associated with Coats disease. A few possible causes have been proposed, such as a genetic cause, relation to other exudative retinopathies with similar ocular phenotype, and vascular endothelial growth (VEGF) immunoreactivity [
7,
8]. There are two mechanisms that cause retinal damage in Coats disease. First, endothelial breakdown of blood-retinal barrier results in plasma leakage, eventually impairing the vessels. Secondly, the presence of abnormal pericytes and endothelial cells in retinal blood vessels leads to formation of abnormal retinal vasculature and aneurysms [
9]. These mechanisms cause exudates to leak into the retina, leading to retinal thickening, cyst formation, and retinal detachment [
9]. Following exudate resolution, subretinal pigmentation and fibrosis usually take place. This may hinder visual recovery, especially if the pathologies are located in the fovea [
1].
In adults, painless vision loss is the most common chief complaint, while child patients usually present with more variable symptoms, such as poor vision, nystagmus, strabismus, and leukocoria [
2,
4,
5]. Coats disease is mainly unilateral, but if bilateral involvement is suspected, the features in one eye are usually more intense than in the other. Therefore, other causes of bilateral exudative retinopathy should also be excluded [
3,
4]. These two cases were first referred with the diagnoses of posterior uveitis. Although the second patient had positive results related to tuberculosis, the first patient reported no systemic risk factors. This is common in clinical practice, as it has been reported that more than 50% of Coats disease cases are referred as other diseases, including retinal and choroidal inflammatory disorders [
3].
Visual acuity in Coats disease usually ranges from normal vision to no light perception, depending on the severity of the disease and macular involvement. In our cases, despite the fact that visual symptoms were present, which we understood as scotomas corresponding with the pathologic lesions, initial visions were good, with both patients showing VA of 6/6 (0 logMAR). This finding is quite rare, even as the majority of older patients with Coats disease reportedly present with better vision compared with child patients. Kang
et al., reported that visual acuities of patients with Coats disease at presentation were similar in both child and adult groups, with mean visual acuity of only 20/162 (0.9 logMAR) [
10]. A cohort study by Dalvin
et al., consisting of large samples of patients with Coats disease, found that younger age (3 years old and younger) at diagnosis is linked to more advanced stage, worse visual prognosis, and higher chance of enucleation [
6].
Retinal telangiectasia, often referred to as “light bulb” telangiectasia, is the characteristic lesions predominantly found in temporal macula and mid-periphery [
3,
10]. Other findings may include subretinal and/or intraretinal exudation, which is composed of cholesterol crystals, most commonly located in the macular area [
1,
3]. Unless hemorrhage, retinal breaks, and neovascularization occur, vitreous is usually clear [
3]. In advanced cases, exudative retinal detachment may develop. Shields classified Coats disease into five stages: stage 1, in which only retinal telangiectasia is found; stage 2, where telangiectasia and exudates are observed; stage 3, in which exudative retinal detachment develops; stage 4, where total retinal detachment and glaucoma are encountered; and stage 5, where the disease has advanced to end stage, occasionally with phthisis bulbi [
1,
2]. Both of our patients were categorized as stage 2 because no retinal detachment was observed. This is concordant with previous studies reporting that nonjuvenile cases are usually diagnosed at stage 2 [
2]. Despite having similar clinical features with juvenile cases, adult patients with Coats disease generally involve smaller retinal area and progress less rapidly [
4‐
6,
10].
Excellent central vision in these two cases was preserved owing to the location of the lesions, where the macula was spared or not significantly affected. In the first case, the retinal exudation and hemorrhage involved only the inferior half of the retina, whereas in the second case, the pathology involved the nasal part of the retina. Kang
et al. found that the childhood group of patients with Coats disease had more frequent macular exudation and significantly diffuse ring exudation [
10]. Most patients with Coats disease usually have normal anterior segment; however, findings like cataract, rubeosis iridis, shallow anterior angle, anterior chamber cholesterolosis, megalocornea, and corneal edema may be observed in some cases [
2,
3].
Other than ophthalmoscopy, several ancillary tests can be utilized to help distinguish Coats disease from other entities, and to monitor the disease progression. FA detects vascular anomalies, such as micro- and macro-aneurysms, areas of telangiectasias, beading of vessel walls, and vascular communicating channels [
2,
3]. OCT helps determine retinal thickening and monitor macular edema [
2,
10]. We performed both FA and OCT on both patients. FA in both cases showed telangiectatic vessels and areas of leakage, while OCT revealed mild subfoveal fluid on our first case upon initial examination (despite normal VA), which subsequently disappeared during follow-up.
Treatment of Coats disease aims to improve vision and preserve ocular anatomy [
1,
11]. Various treatment modalities are available, and the choices depend on the disease severity and surgeon’s preference. Treatment includes cryotherapy, laser photocoagulation, external drainage of subretinal fluid, scleral buckling, and pars plana vitrectomy (PPV). Adjunctive intravitreal injection of corticosteroids and anti-VEGF has also been used in cases with subretinal exudates and macular edema [
2,
12]. Patients with only retinal telangiectasia may be observed vigilantly, but if the disease progresses, treatment needs to be instigated [
1]. As shown in our cases, in mild to moderate Coats disease where telangiectasia and exudates are present with no or mild retinal detachment, laser photocoagulation and cryotherapy are recommended [
1]. In advanced stages where subtotal or total retinal detachment and glaucoma are present, PPV is usually required [
2]. Enucleation may be indicated for end-stage disease with painful eye, while nonpainful eye can be observed without any treatment [
9,
11,
13].
Laser photocoagulation for Coats disease is usually guided by FA, with the laser applied to obliterate defective vessels in order to stop further leakage and initiate exudate resorption [
1]. Cryotherapy may be suitable in cases with peripheral lesions, subretinal fluid, or thick exudation; however, laser photocoagulation is still preferred owing to the possible transient increase in subretinal exudation and transient retinal detachment after cryotherapy [
1]. We decided to treat the patients using laser photocoagulation only, with the aim to treat leaking telangiectasias and promote resorption of subretinal fluid and exudates. Furthermore, because both our patients showed mild to moderate features with little to no macular involvement, we were quite confident in choosing laser photocoagulation monotherapy. We applied focal, FA-guided laser photocoagulation in telangiectatic and nonperfusion areas, leaving healthy tissues intact. Usually, more than one treatment session of laser photocoagulation may be required, especially if more than two quadrants of the eye are involved and if exudation persists after laser treatment [
14]. It is recommended to set the follow-up sessions 1–3 months apart from the previous one, to allow time for exudate resolution and monitor the possible complication of laser [
1].
The first patient responded well to the treatment with no adverse events, and the initial subretinal fluid resolved after laser photocoagulation. On final follow-up, 3 years after laser treatment, retina was stable, showing fibrosis and scarring without active exudation. However, in the second case, there was still remaining exudation and hemorrhage 3 months after laser treatment. This may warrant the need for further investigations, including repeat retinal diagnostic imaging and systemic work-up to exclude other confounding diseases (as the patient tested positive for tuberculosis). The patient may also require further treatment with multimodalities such as additional laser, intravitreal, or periocular triamcinolone, or intravitreal anti-VEGF injections.
The prognosis of Coats disease depends on the severity of the disease. Presence of macular edema, epiretinal membrane, optic atrophy, and subfoveal fluid, as well as exudation, fibrosis, and hemorrhage, contributes to poor vision [
2]. Recurrences may also occur many years later, marked by reappearance of exudates after seemingly successful resolution of the disease. Cataract may occur as a secondary complication of Coats disease. In our first case, the patient later developed cataract, which required surgery. Therefore, owing to possible recurrences and complications, we recommended close monitoring of patients even after the disease has stabilized. Patients are usually advised to have lifelong follow-up visits, preferably once every 6 months [
15].
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