Could a single drop of eye medication share its chemical lineage with nonstick cookware and waterproof jackets? That’s the unsettling question emerging from recent research into per- and polyfluoroalkyl substances (PFAS) now appearing in ophthalmic therapeutics.
PFAS—often dubbed “forever chemicals”—are synthetic compounds characterized by exceptionally strong carbon–fluorine bonds, rendering them highly resistant to environmental degradation and biological elimination. While regulatory agencies worldwide have increasingly restricted PFAS use in food packaging, textiles, and cosmetics, a new frontier has emerged: prescription eye drops for dry eye disease. Two recently approved treatments contain fluorinated compounds—including perfluorohexyloctane (F6H8) and perfluorobutylpentane (F4H5)—which fall squarely within the PFAS chemical class. These agents are prized for their inertness and ability to stabilize the tear film’s lipid layer, yet their persistence, bioaccumulative potential, and newly uncovered metabolic activity raise urgent questions about long-term safety.
A landmark study published in Environment International in January 2026 challenges the longstanding pharmaceutical assumption that F6H8 is metabolically inert. Using human-relevant HepaRG liver cells—a well-validated model for hepatic metabolism—researchers exposed cultures to clinically plausible concentrations of F6H8, simulating systemic exposure following chronic ocular administration. Contrary to expectations, they detected a novel, dose-dependent metabolite: perfluorohexyloctanoic acid (F6H8-COOH), formed via oxidative modification of the parent compound’s terminal alkyl chain. Structural characterization confirmed the addition of a carboxylic acid group—a transformation strongly suggestive of cytochrome P450–mediated oxidation, a pathway previously presumed inactive toward F6H8.
This metabolic conversion carries profound toxicological implications. While F6H8 itself showed modest associations with cellular metabolites, its carboxylated derivative correlated significantly with over 280 metabolites—seven times more than the parent compound. The metabolite disrupted core hepatic pathways, including amino acid catabolism, mitochondrial energy metabolism (TCA cycle and oxidative phosphorylation), bile acid synthesis, and sphingolipid homeostasis. It also triggered robust oxidative stress and mitochondrial dysfunction—hallmarks of early hepatocellular injury.
Further lipidomic profiling revealed widespread perturbation of membrane phospholipids and signaling lipids. At low concentrations, F6H8 preferentially altered sphingolipid and glycosphingolipid metabolism—changes linked epidemiologically to insulin resistance and drug-induced liver injury. At higher exposures, disturbances expanded to central carbon metabolism and amino acid degradation, indicating failure of compensatory mechanisms and impaired cellular energetics. Notably, the metabolite—but not F6H8—upregulated primary bile acid synthesis, purine metabolism, and the urea cycle, suggesting interference with nitrogen excretion and bile acid homeostasis—processes critical to hepatic detoxification capacity.
Additional red flags emerged at the subcellular level: acylcarnitines—essential carriers for mitochondrial fatty acid β-oxidation—declined progressively with exposure, implying compromised energy substrate utilization. Concurrently, the lysophosphatidylcholine-to-phosphatidylcholine ratio increased—a biomarker of membrane remodeling stress often associated with inflammation and lysosomal dysfunction.
These findings underscore that F6H8 is not merely a transient, pharmacokinetically benign agent. Preclinical evidence shows structurally analogous semi-fluorinated compounds accumulate in liver tissue at concentrations double those in blood, with elimination half-lives extending to weeks. Rabbit studies confirm systemic absorption after a single ocular dose, with measurable F6H8 persisting in plasma for at least 24 hours. Given that many dry eye patients require lifelong, multi-daily dosing, the potential for cumulative hepatic exposure—and progressive metabolic disruption—cannot be dismissed.
This prompts a broader therapeutic reckoning: Is PFAS-based therapy truly necessary for dry eye management? Established alternatives—including preservative-free artificial tears, topical cyclosporine, lifitegrast, and autologous serum eye drops—lack fluorinated components and demonstrate robust clinical efficacy. Critically, pivotal F6H8 trials used hypotonic saline as a placebo control—a formulation not aligned with current clinical guidelines for dry eye. This design may inflate apparent treatment benefit compared to standard-of-care interventions. Moreover, the European Medicines Agency has flagged fluorinated excipients in anhydrous delivery systems as posing environmental contamination risks, mandating specialized disposal protocols to prevent wastewater release.
Scientific rigor demands neither alarmism nor dismissal. F6H8 offers tangible relief for select patients with severe, refractory evaporative dry eye. But its approval occurred before modern metabolomic and systems toxicology tools were routinely applied to ophthalmic agents. As regulators and clinicians weigh benefit–risk profiles, ongoing surveillance—particularly longitudinal studies assessing hepatic enzymes, bile acid profiles, and metabolic biomarkers in chronic users—is essential. Ultimately, this case illustrates a larger principle: when “forever chemicals” enter medicine, their inertness must be empirically verified—not assumed. The eye may be the window to the soul, but what travels through that window may reach far deeper than we once imagined.