The idea of crying crystals seems like a fictional concept, yet the physiological possibility is grounded in the basic chemistry of human tears. Tears can and do crystallize under the right conditions, though a person will not typically weep large, perfectly formed diamonds. This process involves the concentration of the natural salts and proteins dissolved in the tear film. This phenomenon happens mildly under normal circumstances but can become dramatically visible due to environmental factors or specific medical conditions.
The Composition of Human Tears
The fluid that bathes the eye, known as the tear film, is a complex, multi-layered liquid designed for protection, lubrication, and nourishment of the ocular surface. Tears are primarily composed of water, making up about 98% of the total volume, but the remaining two percent contains hundreds of dissolved substances. These dissolved materials include electrolytes, proteins, lipids, and various metabolic byproducts. The salty taste of tears comes from these electrolytes, primarily sodium chloride, which is present in a concentration similar to that found in blood plasma.
The tear film organizes itself into three distinct layers to function effectively. The innermost mucin layer adheres the tear film to the eye’s surface, allowing the watery component to spread evenly. The thickest section is the middle aqueous layer, which contains the bulk of the water, dissolved salts, and antimicrobial proteins that fight infection. The outermost lipid (oily) layer acts as a barrier, preventing the rapid evaporation of the aqueous layer beneath it.
The Science of Tear Crystallization
The transformation of liquid tears into solid crystals is a physical process dependent on the principles of concentration and saturation. When the water component of the tear solution is removed, the concentration of the remaining dissolved solids, such as sodium chloride and proteins, increases significantly. This process is known as evaporation, and it is the primary driver of tear crystallization outside of a disease state. As water molecules escape into the surrounding air, the solution becomes increasingly concentrated until it reaches a point of supersaturation.
Supersaturation occurs when the solution contains more dissolved material than it can normally hold at that temperature. Once this threshold is crossed, the dissolved solutes precipitate out of the solution, forming an ordered, solid structure through nucleation. These microscopic solids then grow by adding more molecules in a repeating pattern, forming visible crystals. Environmental factors, such as low humidity or wind, accelerate the rate of water evaporation, leading to rapid supersaturation. This mechanism explains the visible salt crusts that form on the face after tears have dried and left the concentrated solids behind.
Rare Medical Causes of Crystalline Tears
While simple evaporation can cause a salt crust, the formation of true crystalline structures within the eyes often points to an underlying imbalance in body chemistry. One of the most significant and rare causes is Cystinosis, a genetic lysosomal storage disorder. This inherited metabolic disorder is caused by a mutation in the CTNS gene, which transports the amino acid cystine out of cellular lysosomes. When the transport protein is defective, cystine accumulates within the cells and begins to form crystals throughout the body, including the eyes.
These cystine crystals are pathognomonic and can be seen with a slit lamp examination, often appearing as shimmering, needle-shaped deposits within the cornea and conjunctiva. The accumulation of these crystals in the cornea can lead to photophobia, or extreme sensitivity to light, which is often the earliest ocular symptom. Although the crystals are primarily deposited in the eye tissue, they can sometimes be shed into the tear film, causing the body to weep crystalline material.
Other factors that lead to extreme tear hyperosmolarity (high salt concentration) can also contribute to crystallization. Hyperosmolarity is a hallmark of severe dry eye disease, where insufficient aqueous production or excessive evaporation leaves behind a highly concentrated tear film. This high concentration of electrolytes creates the ideal environment for dissolved salts to precipitate into micro-crystals on the ocular surface. Certain systemic conditions, such as infectious diseases or metabolic disorders causing Fanconi syndrome, can also alter tear chemistry, making crystallization more likely. These crystals are often micro-deposits, visible only under magnification, but they represent a tangible, scientific reality of “crying crystals.”