Choroidal folds are ripple-like wrinkles or striae that develop in the choroid layer of the eye. The choroid is a dense network of blood vessels situated between the retina and the outer white layer, the sclera. The presence of these folds is not a disease in itself but rather a physical sign indicating mechanical stress on the eye’s structure. While sometimes an incidental discovery, they often serve as an important clue to a specific local or systemic condition that requires investigation.
Defining Choroidal Folds
The choroid is a highly vascular tissue that provides oxygen and nourishment to the outer layers of the retina. Choroidal folds are visible as alternating dark and bright lines beneath the retina, resembling grooves or stripes. These undulations involve the inner choroid, the adjacent Bruch’s membrane, and the retinal pigment epithelium.
The folds are typically observed in the posterior pole of the eye, including the macula and optic nerve. They commonly appear as parallel, horizontal lines radiating from the optic nerve, although they can also be vertical, oblique, or irregular. The formation of these wrinkles results from biomechanical stress, where the tissue is compressed, swollen, or buckled due to changes in surrounding eye structures. This mechanical force causes the choroid and its attached layers to shorten, resulting in the characteristic folding pattern.
Underlying Causes and Associated Conditions
Choroidal folds manifest due to various mechanical stresses acting on the eye, and identifying the specific source is necessary for appropriate management. These causes can be broadly grouped into conditions that increase pressure outside the eye, those that decrease pressure inside the eye, and those that cause tissue swelling or thickening.
One major category involves space-occupying lesions in the orbit. Tumors, such as cavernous hemangiomas or optic nerve meningiomas, can press on the back of the eyeball, flattening the globe and inducing folds. Inflammatory conditions like Thyroid Eye Disease also cause the muscles around the eye to enlarge, increasing orbital pressure and pushing on the eye wall.
Another mechanism involves conditions that cause the eye’s internal pressure to drop significantly, known as ocular hypotony. This can occur following certain eye surgeries, like glaucoma filtration procedures, where there is excessive drainage of fluid. When the intraocular pressure falls below 6 mmHg, the reduced internal volume allows the eye wall to buckle inward, creating broad, randomly oriented choroidal folds.
Inflammatory conditions affecting the eye wall, such as posterior scleritis, can also lead to fold formation. Scleral inflammation causes the outer white layer of the eye to thicken and swell, which shortens the inner surface and forces the choroid to wrinkle. Finally, some cases are termed “idiopathic,” meaning no underlying cause is found despite a thorough investigation, although improved imaging methods have reduced the frequency of this diagnosis to around 15% of cases.
Recognizing Visual Symptoms and Detection Methods
The visual impact of choroidal folds depends on whether the folds extend into the macula, the area responsible for sharp central vision. Patients may experience reduced visual acuity (blurred vision) or metamorphopsia, where straight lines appear wavy or distorted because the folds disrupt the smooth surface of the retina.
A significant finding associated with these folds is an acquired hyperopic shift, where the eye becomes more farsighted due to the mechanical flattening of the globe. Ophthalmologists rely on several diagnostic tools to confirm the presence of folds and investigate their cause. Fundus photography allows for a clinical view of the eye’s back pole, often highlighting the alternating light and dark bands of the folds.
Fluorescein angiography (FA) involves injecting a dye into the bloodstream, which highlights the folds as alternating bands of bright (hyperfluorescent) and dark (hypofluorescent) streaks. Optical Coherence Tomography (OCT) provides a high-resolution, cross-sectional view of the eye’s layers. OCT scans clearly demonstrate the wavy, corrugated appearance of the choroid, Bruch’s membrane, and retinal layers, confirming the presence of the folds.
Management and Long-Term Outlook
Management is directed at treating the specific underlying condition that caused the mechanical stress. There is no direct treatment for the folds themselves; they serve as a marker that resolves once the causative issue is addressed. For folds caused by orbital tumors, surgical removal of the mass relieves pressure on the globe, leading to resolution.
If the folds are secondary to inflammation, such as posterior scleritis or thyroid eye disease, treatment involves medications to manage swelling and reduce tissue thickness. In cases of hypotony, efforts focus on surgical or medical intervention to normalize the eye’s internal pressure. The prognosis is generally favorable, with visual changes often resolving once the underlying condition is stabilized. However, if the folds are long-standing or the pressure is prolonged, permanent changes to the retinal pigment epithelium can occur, potentially leading to persistent visual distortion.