Pachychoroid Spectrum

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Pachychoroid Spectrum refers to a group of clinical entities that have a common characteristic: a pachychoroid. This term derives from greek παχύ, pachy, thick. It refers to a anatomic choroidal characteristic, in which a thickened choroid is present. This could be inferred by some specific and common clinical characteristics between this entities and funds tessellation. It can be studied and visualized with Enhanced Depth Imaging optical coherence tomography (EDI-OCT) or Swept Source OCT (SS-OCT).

Pachychoroid Spectrum

Choroid Anatomy

First we must understand and define the normal choroidal anatomical characteristics. The choroid is responsible for the external 1/3 vascular support of the retina and its functional and structural integrity is essential for normal retinal function. A compromised volume or flow in its circulation could result in photoreceptor and retinal pigment epithelium (RPE) dysfunction and death. The choroidal blood supply derives from branches of the anterior and posterior ciliary arteries. The choriocapillaris has large diameter capillaries (20-25 μm), also it has fenestrations of 700-800 nm diameter, which allows more rapid transport and of bigger molecules.

Histologically, the choroid is composed of 5 layers which are in order from inner (retinal side) to outer (scleral side) are:

  1. Bruch Membrane
  2. Ruysch Layer (Choriocapillaris)
  3. Sattler's Layer (Layer of medium diameter blood vessels)
  4. Haller´s Layer (Layer of large diameter blood vessels)
  5. Suprachoroidea (Transitional zone between choroid and sclera)

Choroid OCT Anatomy

Through the use of EDI–OCT and SS-OCT, we are able to define some important anatomical characteristics. The choroid is thickest in subfoveal region, thinner in nasal region and has a progressive thinning through temporal region. Subfoveal choroidal thickness (SFCT) is approximately 300 microns, and the median choroidal thickness is approximate 260 microns, however, thickness varies based on characteristics such as age, gender, ethnicity and other factors including the measuring instrument. There is an age-related choroidal thickness reduction about 10-15 microns per decade of life. Examining the choroidal layers, submacular central thickness in Sattler's layer is approximately 87 +/- 56 microns and Haller's layer is approximately 141 +/- 50 microns.

Disease

Pachychoroid Spectrum refers to a group of clinical entities that have a common characteristic of a thickened choroid and share an underlying pathological mechanism. This entities are pachychoroid pigment epitheliopathy, central serous chorioretinopathy (CSC), pachychoroid neovasculopathy and polypoidal choroidal vasculopathy. There have been some other entities described that are associated with a pachychoroid including Vogt-Koyanagi-Harada disease, multiple evanescent white dot syndrome and multifocal choroiditis. [need ref]

Etiology

Among its common characteristics are a thick choroid with dilated and hyperpermeable vessels, which may cause focal Bruch's membrane and RPE disruption that could lead to serous retinal detachment.

Risk Factors

Common risk factors include: "Type A" personality, emotional stress, pregnancy, tobacco use, corticosteroids, and other sympathomimetics. Certain herbal supplements may also have glycogenic properties that can be associated with pachychoroid development.

Specific Pathologies

Pachychoroid Pigment Epitheliopathy

Clinical Findings

Silent Disease: Normal visual acuity. Orange-Redish, absence of fundus tessellation, RPE lesions that could cause drusenoid fundus without subretinal fluid. Also called forme fruste central serous chorioretinopathy

Ancillary Testing

OCT: Thick choroid and large choroidal vessels beneath elevations on RPE and sub-RPE drusen like deposits. ICGA (Indocyanine Green Angiography): Choroidal hyperpermeability and hyperpermeability co-existent with areas of RPE change. FAF (Fundus Autofluorescence): Granular and mixed stippled hyper-hypoautofluorescence.

Central Serous Chorioretinopathy

Clinical Findings

It commonly presents at age 20-50, with a gender predilection of male:female 6:1, has an incidence about 5-6/100,000, best corrected visual acuity 20/20 – 20/200 with a median 20/30. Characteristic presenting symptoms include metamorphopsia, blurred vision, micropsia, relative scotoma. Findings typically resolve within 6 months. When findings persist for a longer period it may be classified as chronic CSC.

Physical Examination

Can present as a bullous, inferior non-rhegmatogenous peripheral retinal detachment, also could find an absent foveal reflex, yellow-gray elevation and speckled or grouped RPE (this finding may suggest chronicity).

Ancillary Testing

OCT: Pachychoroid + RPE detachment + subretinal fluid. ICGA: Choroidal congestion and hyperpermeability with multifocal hypofluorescent areas. Fluorescein angiography (FA): RPE detachment with focal leak that ends in pooling in less than a disk diameter from foveal region. FAF: Speckled Hyperautofluorescence and eventually gravitational zones.

Risk Factors

Type A personality, emotional stress, systemic hypertension, gastroesophageal reflux disease, pregnancy, organ transplantation, systemic lupus erythematosus, tobacco, alcohol, membranoproliferative glomerulonephritis type II, Helicobacter pylori infection, autoimmune disorders. Medications: corticosteroids, psychopharmacologic medications, MDMA, antacids and anti-reflux medications, over-the-counter sympathomimetics, antibiotics, antihistamines, sildenafil citrate.

Differential Diagnosis

Choroid neovasculopathy, optic disc pit, choroidal polypoidal vasculopathy, choroidal melanoma, choroidal metastasis, peripheral retinal break, choroidal hemangioma, uveitis, Harada disease, optic neuritis, papilledema, vitreal traction, macular hole, systemic hypertension.

Treatment

The initial treatment of choice is observation cause the majority of cases solve spontaneously, if fail to improve in 3-6 moths, it should be considered treatment with laser photocoagulation (if leakage zone is > 200 microns of foveal region) or photodynamic therapy.

Prognosis

Almost always the patient will have visual acuity 20/40 or above, but metamorphosis may persist .

Pachychoroid Neovasculopathy/ Polypoidal Choroidal Vasculopathy

Clinical Findings

Blurred vision. (Visual acuity near 20/50). Reduced fundus tessellation without serous retinal detachment.

Ancillary Testing

OCT: Pachychoroid with neovascularization type 1 (sub RPE), large choroidal vessels obliterating choriocapillaris and Sattler's layer. Choroidal vessels between Bruch membrane and RPE, also the “double layer sign”. These changes could progress to polypoidal vascular lesions (Polypoidal Choroidal vasculopathy). ICGA: Choroidal hyperpermeability with hyperfluorescent early dots and vascular network with dilated choroidal vessels. This vessels could progress to polypoidal vasculopathy.

Treatment

Anti-VEGF and/or photodynamic therapy may be considered in cases of chronic CSC.


References

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