A Hudson-Stähli line is a tiny deposit of iron on the clear front of the eye, and it is not dangerous. It is one of the most common things eye doctors see, and it becomes almost universal as people get older.1PubMed. Prevalence of the Hudson-Stähli line of the cornea Finding one usually says more about your age and the way your tears move across your eye than about any disease.
What the Line Actually Is
The cornea is the clear, dome-shaped window at the front of the eye, and its outer skin is a thin layer of cells. The line forms in the bottom row of those surface cells.2PubMed Central. Iron homeostasis and eye disease Those cells hold iron packed into the body’s normal iron-storage protein.3PubMed. Corneal iron lines after refractive keratoplasty So it is stored iron of the same kind your body keeps everywhere, not a growth, scar, or infection.4PubMed Central. Iron homeostasis and eye disease
It is usually too faint to see in a mirror. It shows up when a doctor looks through a slit lamp, the bright microscope used in eye exams.5PubMed Central. Iron homeostasis and eye disease Through that microscope it looks like a thin yellow-brown or rust-tinted line, often slightly wavy. It is typically horizontal and runs across the lower third of the cornea.6Ophthalmology Review. Corneal Iron Lines — Ophthalmology Review When your eyes are open, it usually lies at about the level of the lower eyelid edge, and it is often present in both eyes. Most people never notice it themselves.
The line is horizontal because it follows the place where the upper and lower eyelid edges meet when you blink. That contact zone sits in the lower part of the cornea, not across the middle, where you look straight ahead.
Doctors often write it down in passing during a routine check, so many people first learn about it from their chart. On that chart it may appear as Hudson-Stähli line, HS line, or corneal iron line. It is named after two doctors who described it.
Is a Hudson-Stähli Line Dangerous
Corneal iron lines cause no symptoms and are considered benign.7Ophthalmology Review. Corneal Iron Lines — Ophthalmology Review Eye specialists regard the Hudson-Stähli line as typically harmless.8PubMed Central. Enhancing Safety in Refractive Surgery: A Pilot Evaluation of In Vivo Confocal Microscopy It does not need drops, surgery, or removal.
It also doesn’t blur your sight. The iron sits in a very thin layer of cells and usually lies low on the cornea.9Ophthalmology Review. Corneal Iron Lines — Ophthalmology Review
It also can’t be linked to the iron in your blood. The iron in the line is stored locally by surface cells of the cornea, and it does not reflect how much iron is circulating in the rest of your body. Anemia and iron overload are diagnosed with blood tests, not by looking at the cornea, so the line can’t be used to diagnose them. It is no reason to change your diet or your supplements.
Some symptoms point elsewhere. Pain, redness, or sensitivity to light suggest something else, such as inflammation, infection, or a scratch, and they should be checked on their own. A sudden blur or a spot you can see in a mirror deserves a prompt exam, even if you were told about the line before.
Why It Forms and Who Gets It
In one large exam, about 5 in 100 eyes of people aged 11 to 20 had the line.10PubMed. Prevalence of the Hudson-Stähli line of the cornea By ages 81 to 90, every eye had it.11PubMed. Prevalence of the Hudson-Stähli line of the cornea Nearly 9 in 10 people over 50 had it.12PubMed. Prevalence of the Hudson-Stähli line of the cornea Up to age 60 it is somewhat more common in men.13PubMed. Prevalence of the Hudson-Stähli line of the cornea It is slightly more common in people with brown or green eyes than blue or grey, though it rises with age in everyone.14Nature. The Hudson-Stahli line I: An epidemiological study
Age matters because the cells in the cornea’s skin constantly replace themselves. As we get older that turnover slows, so iron has more time to collect. The line usually grows longer and darker slowly, over decades.
The leading explanations center on tears. The line sits where the eyelids meet during blinking, where tears tend to linger.15Ophthalmology Review. Corneal Iron Lines One idea is that iron, a normal trace component of the tear film, settles into the nearby surface cells over time.16Ophthalmology Review. Corneal Iron Lines Another is that older surface cells renew more slowly and hold on to iron.17Ophthalmology Review. Corneal Iron Lines Eyes with the line tended to make more tears in one study, not fewer.18Nature / Eye. Corneal topography and Schirmer testing in eyes with the Hudson-Stahli line No single explanation has been proven, so these are best read as well-supported theories.
Several things do not cause it. Eating too much iron or taking supplements doesn’t, and neither do sun, injury, or poor hygiene. Having it in only one eye also happens and is normal.
Contact Lenses, LASIK, and Other Eye Procedures
Long-term contact lens wearers get the line about as often as non-wearers of the same age.19PubMed. The Hudson-Stahli line. II: A comparison of properties in eyes with and without long-term contact lens wear Lens wear can, however, make the line shorter and fainter, broader, or occasionally shifted.20PubMed. The Hudson-Stahli line. II: A comparison of properties in eyes with and without long-term contact lens wear A line that looks different from a friend’s, or from your own earlier exam, is not a sign the lenses are harming your eyes.
Surgery is a separate matter. Reshaping the cornea can produce new iron lines of their own.21PubMed. Corneal iron lines after refractive keratoplasty Before laser vision correction, the surgeon maps the shape and thickness of your cornea with a scanner, and those measurements decide whether you are a candidate. The line is noted but is not a reason to cancel on its own. In one reported case, a woman with the line was turned down for surgery because of a separate weakness in her cornea, not the line.22PubMed Central. Enhancing Safety in Refractive Surgery: A Pilot Evaluation of In Vivo Confocal Microscopy
Surgery or devices that reshape the cornea change its surface contours, which alters how tears flow and pool, and iron may collect along the new contours. New arcs near a ring or reshaped area are also harmless.
They can fade, too. Iron arcs from overnight reshaping lenses faded within about 2 months of stopping.23Optometry and Vision Science. Reversibility of Corneal Pigmented Arc Associated with Orthokeratology After removal of corneal ring implants, lines returned to a Hudson-Stähli pattern or vanished.24PubMed. Corneal iron lines associated with the intrastromal corneal ring
How It Differs From Rings That Signal Disease
A Kayser-Fleischer ring is a copper ring at the edge of the cornea seen in Wilson’s disease, an inherited copper disorder. Similar-looking rings appear with long-term liver bile-flow diseases, keratoconus, age-related lines like the Hudson-Stähli line, and silver or gold exposure.25Neurology India Case Reports. Pigmented Corneal Rings: Not Always Wilson’s Disease – The Enigmatic Coexistence of Kayser–Fleischer Ring in a Case of Subacute Sclerosing Panencephalitis None of these involve the body-wide copper buildup of Wilson’s disease.26Neurology India Case Reports. Pigmented Corneal Rings: Not Always Wilson’s Disease – The Enigmatic Coexistence of Kayser–Fleischer Ring in a Case of Subacute Sclerosing Panencephalitis
A Fleischer ring is another iron line. It forms around the base of a cone-shaped cornea in keratoconus.27Neurology India Case Reports. Pigmented Corneal Rings: Not Always Wilson’s Disease – The Enigmatic Coexistence of Kayser–Fleischer Ring in a Case of Subacute Sclerosing Panencephalitis It points to a corneal shape problem, unlike the Hudson-Stähli line.
Location and look separate them. The Hudson-Stähli line is a short horizontal band low on the cornea, with clear tissue above and below it, and it never forms a full circle. The copper ring of Wilson’s disease runs around the outer edge of the cornea as a brown, golden, or greenish band, sometimes starting at the top and bottom first. A Fleischer ring forms a partial or full circle around the base of a bulging cone, so it sits closer to the center.
The copper ring can be faint and hard to see, so doctors check for it with the microscope and sometimes with additional imaging. The answer should come from your eye doctor’s exam, not from comparing photos online.
More tests happen only with other signs. A copper ring at the corneal edge together with liver trouble, tremor, or movement or mood changes would lead a doctor to order copper tests for Wilson’s disease. A ring around a bulging area with blurry or changing vision would lead to mapping the cornea’s shape for keratoconus. A low horizontal line on its own, with no such symptoms, calls for neither.
What Happens Over Time
Because the line becomes more common each decade, one found in midlife will most likely stay. In brown- or green-eyed lens wearers, its length and darkness stayed almost the same from their 20s to 50s.28PubMed. The Hudson-Stahli line. II: A comparison of properties in eyes with and without long-term contact lens wear Small differences in how a doctor describes it from one visit to the next can come from different lighting, different equipment, or a different examiner, not a real change.
No special visits are needed. Your usual eye exam schedule is enough, and the doctor may simply note it again each time.
Nothing you do will make it go away, and nothing is needed to stop it forming. Eye drops won’t dissolve it, and cutting dietary iron won’t remove it.