Drug abuse retinopathy is damage to the retina of the eyes caused by chronic drug abuse. Types of retinopathy caused by drug abuse include maculopathy, Saturday night retinopathy, and talc retinopathy. Common symptoms include temporary and permanent vision loss, blurred vision, and night blindness. Substances commonly associated with this condition include poppers, heroin, cocaine, methamphetamine, tobacco, and alcohol.
Retinopathy
Retina is the innermost layer of the eye. It is made up of three layers, namely the outer pigmented layer, the middle photoreceptor layer and the inner neural layer. The pigmented layer is responsible for absorbing light that penetrates inner neural layer. The photoreceptor layer consists of 2 kinds of photoreceptor cells, rod cells and cone cells. Rod cells have high sensitivity to light so they are responsible for night vision, but they cannot differentiate between colors, meaning that they only have black and white vision. Cone cells have low sensitivity to light, but they have the ability to differentiate between colors. These photoreceptors cells are unevenly distributed throughout the retina. The density of rod cells increases peripherally and the cone cells are concentrated at a region called macula where there are no rod cells. This region is responsible for high-resolution and color vision.
Maculopathy
Maculopathy is an eye disease that refers to breakdown of the macula. Macula is the region on the retina containing the highest concentration of cone cells which is responsible for color vision. Symptoms of maculopathy include a reduction in central vision acuity, distorted vision, and perceived flashes of light that occur without an actual light source.
Saturday night retinopathy
Saturday night retinopathy is a condition that is due to central retinal or ophthalmic artery occlusion. Common clinical features include ophthalmoplegia and orbital congestion. The etiology of this condition is related to unconsciousness after drug use, leading to patient sleeping in an unusual position that continuously exerts pressure on the orbit. This orbital compression will result in ophthalmic and central retinal artery occlusion which lead to ischemia in the inner retina and the patient may experience sudden unilateral blindness and eye pain.
Talc retinopathy
Talc is a filler commonly added in tablet formulation acting as a glidant to improve the flowability of the drug powder. It is also frequently added as an adulterant in illicit drugs such as heroin and methamphetamine to increase its volume and weight and thus its street value. When it is inhaled, it will enter the systemic circulation through the capillaries in the nasal mucosa. After entering the systemic circulation, it will deposit in the retinal blood vessels and undergo reaction which lead to focal narrowing of retinal vessels. This significantly reduces the blood flow to retina and eventually lead to retinal ischemia. Clinical features include refractile yellow deposit seen under fundoscopy. Patients may experience a reduction in visual field and visual acuity.
Disease causing agents
Alkyl nitrites (poppers)
Poppers is an inhaled drug which contains a range of alkyl nitrites, such as isobutyl nitrite and amyl nitrite. Despite its primary usage as a potent vasodilator, its popularity among the homosexual community largely stems from its ability to facilitate anal sexual intercourse by relaxing the smooth muscles in the internal anal sphincter. The use of intranasal poppers is associated with the development of macular degeneration through a poorly known mechanism. This condition may be the consequence of the increase in nitric oxide (NO) level following the oxidation of alkyl nitrites. The increase in NO level exerts a more significant stimulatory effect on guanylate cyclase, an enzyme found in cone cells. Upon activation, guanylate cyclase converts more guanosine triphosphate (GTP) to cyclic guanosine monophosphate (cGMP). cGMP is involved in the photo-transduction pathway which allows calcium and sodium to enter and depolarize the cell. A high level of cGMP results in high levels of calcium in the cells. The increase in intracellular cGMP and calcium level results in the production of reactive oxygen species (ROS) which damage macular cone cells and leading to macular degeneration.