In medicine, the fundus is the part of a hollow organ that sits farthest from its opening. The term comes up across several areas of the body, most commonly in reference to the eye, the uterus, and the stomach. Depending on the organ, the fundus can be at the top or the bottom, which sometimes causes confusion, but the underlying idea is the same: it’s the wide, rounded portion opposite where things enter or exit.
The Fundus of the Eye
When doctors refer to “the fundus” without specifying an organ, they usually mean the inside back surface of the eye. This area includes the retina, the macula (the central zone responsible for sharp vision), the optic disc (where the optic nerve connects), the fovea (the tiny pit at the center of the macula), and the network of blood vessels that supply them all.
The ocular fundus is uniquely important because it’s one of the only places in the body where a doctor can directly observe blood vessels without surgery. A fundoscopic exam, sometimes called ophthalmoscopy, involves shining a light through the pupil to view these structures. The exam can reveal far more than eye problems. Because the blood vessels in the back of the eye reflect what’s happening throughout the body, a single look can help detect or stage diabetes, high blood pressure, and increased pressure inside the skull. Swelling of the optic disc, called papilledema, can signal conditions as serious as brain tumors, meningitis, or severe hypertension. Tiny hemorrhages or pale spots on the retina can point to infections like endocarditis, connective tissue disorders, or HIV-related complications. Characteristic changes to the optic cup can indicate glaucoma.
This is why eye exams are recommended even for people with no vision complaints, particularly if you have diabetes or high blood pressure.
The Fundus of the Uterus
The uterine fundus is the broad, curved top of the uterus, opposite the cervix. Outside of pregnancy, it’s not something most people think about. During pregnancy, it becomes a practical measuring tool.
As the uterus expands, the fundus rises higher in the abdomen. Fundal height, the distance from the pubic bone to the top of the uterus measured with a tape measure, gives a quick estimate of fetal growth. After about 20 weeks of pregnancy, the measurement in centimeters roughly matches the number of weeks along you are, plus or minus 2 to 3 centimeters. So at 32 weeks, a fundal height between about 29 and 35 centimeters is considered normal. This simple check can flag potential concerns like too much or too little amniotic fluid, a baby measuring larger or smaller than expected, or a baby in an unusual position.
The correlation between centimeters and weeks holds from roughly week 20 through week 36. Before 20 weeks, the uterus hasn’t risen high enough to measure reliably from the outside. After 36 weeks, the fundal height often decreases as the baby drops lower into the pelvis in preparation for delivery.
The Fundus of the Stomach
The gastric fundus is the dome-shaped upper portion of the stomach, tucked just beneath the diaphragm. Its main job is to act as a reservoir. When you eat, a reflex triggered by swallowing causes the fundus and the body of the stomach to relax, making room for incoming food. This relaxation is remarkably efficient: the stomach can accommodate up to 1.5 liters of extra volume with only a small rise in internal pressure.
Food sits largely unmixed in the fundus for up to an hour. During that time, the stomach sorts its contents by density, with fats floating to the top. This layering matters for digestion because fats trigger hormonal signals from the small intestine that slow stomach emptying, giving the body more time to process a rich meal.
The gastric fundus also plays a role in one of the most common surgical treatments for severe acid reflux. In a Nissen fundoplication, a surgeon wraps the fundus around the bottom of the esophagus to reinforce the valve that keeps stomach acid from rising upward. The wrap can be partial or a full 360 degrees, and it physically strengthens a barrier that medications alone sometimes can’t fix.
The Fundus of the Gallbladder
The gallbladder fundus is the rounded, free-hanging tip of the gallbladder, the part that projects slightly beyond the edge of the liver and touches the front of the abdominal wall. During an episode of acute gallbladder inflammation, this contact point is where tenderness is most intense, located near the intersection of the lower right rib cage and the edge of the abdominal muscles. Pressing there while a patient breathes in is a classic physical exam finding.
A harmless anatomical variant called a Phrygian cap, a small fold in the fundus, occasionally shows up on imaging and can be mistaken for a liver mass. It requires no treatment and causes no symptoms.
The Fundus of the Bladder
In the urinary bladder, the fundus refers to the base, the lowest portion at the back. This is the opposite of the uterus and stomach, where the fundus sits at the top. The bladder’s fundus contains the trigone, a smooth triangular area where both ureters (the tubes carrying urine from the kidneys) connect and where the urethra exits. It’s a critical junction: urine flows in from above and out through the bottom, all within this small patch of tissue at the fundus.
Why the Same Word Means Different Locations
The common thread is anatomical, not directional. Fundus always refers to the part of a hollow organ that is farthest from its opening. In the stomach, the opening is at the bottom (where food exits into the intestine), so the fundus is at the top. In the bladder, the opening is at the bottom (the urethra), but the ureters enter from above, making the base the portion most remote from the exit. In the eye, the opening is the pupil at the front, placing the fundus at the back wall.
Once you understand that “fundus” means “the far end from the door,” the term makes sense no matter which organ it’s applied to.