Glossary

Latin shorthand used on eye records: OD is the right eye (oculus dexter), OS the left eye (oculus sinister), OU both eyes.

The retina's output neurons. Their axons run across the retina, gather at the optic disc and form the optic nerve. Glaucoma is the gradual loss of these cells.

The ring of nerve tissue between the edge of the cup and the edge of the disc. It holds the axons, so it thins as glaucoma advances.^[9]

In most healthy discs the rim is widest Inferiorly, then Superiorly, Nasally and Temporally. Glaucoma often breaks this order first at the inferior or superior pole.^[10]

A sieve-like plate of collagen in the optic nerve head through which the axons leave the eye. Strain here from eye pressure is thought to injure them.

IOP above 21 mmHg without damage to the optic nerve. It raises the risk of glaucoma, but many people with it never develop the disease.

Goldmann tonometry is calibrated for an average cornea of about 520 µm. A thicker cornea reads falsely high and a thinner one falsely low.^[4]

Goldmann applanation is the clinical reference; rebound and air-puff devices are also common. Readings differ between devices, one reason IOP doesn't transfer cleanly between datasets.

A confocal scanning laser device that measures optic disc topography: disc, rim and cup areas, cup volume and the linear cup-to-disc ratio. The LSMU morphometry uses these HRT-style parameters.^[37]

Perimetry measures light sensitivity at many points of the visual field. MD summarises the average deviation from age-matched normal values, in decibels; more negative is worse.

β-blockers, ACE inhibitors, angiotensin receptor blockers, calcium-channel blockers and diuretics lower blood pressure in different ways. GlaucomAI derives classes from drug names. Calcium-channel blockers have been trialled in NTG for their effect on blood flow.^[38]

An IOP-lowering eye drop. Part of the dose reaches the bloodstream and can slow the heart and lower blood pressure, which matters for perfusion.

The average arterial pressure over one heartbeat, estimated as diastolic + ⅓ × (systolic − diastolic).

Diastolic blood pressure minus IOP: the pressure driving blood into the eye at the low point of each heartbeat. Values below 50 mmHg are linked with more glaucoma.^[19]

Blood pressure normally dips during sleep. A deep dip lowers perfusion at night, when IOP measured lying down can be higher; it has been linked with glaucoma progression.^{[22, 23]}

Also called Flammer syndrome: a tendency of vessels to react inappropriately, with cold hands, low blood pressure and sometimes migraine. It is more common in NTG.^[8]

Active neurons signal nearby vessels to widen so that blood flow matches demand. The flicker test uses this reflex to probe the retina's vessels.^[26]

The LSMU cohort's pulsation measure, recorded with an ultrasound-based Sonovum device. What the amplitude physically represents is still being confirmed with the clinic, so GlaucomAI compares it only with age- and sex-matched controls.

A colour photograph of the back of the eye taken through the pupil. It shows the optic disc, the cup, the vessels and the macula.

A B-scan is one OCT cross-section. A volume is a stack of B-scans covering an area such as the optic disc.^[16]

An image-sized map that labels every pixel, here as disc, cup or background.

Overlap between two outlines: 2 × shared area ÷ (area A + area B). 1.0 is a perfect match and 0 means no overlap.^[15]

Random flips, rotations and brightness or colour changes during training, so the model learns the anatomy rather than one camera's look.

Averaging a model's predictions over simple variants of the input. GlaucomAI averages the photo and its mirror image.

GlaucomAI refuses a photo when the disc it finds is implausibly small or large (outside 3–35% of the image's long side) or contains no cup, instead of guessing.

Doctors outlining the same cup disagree too. The ± on the Try page is the typical spread between Chákṣu's five experts for a cup of that size.^[12]

Finds how far one image is shifted relative to another from the phase of their Fourier transforms. The flicker tracker uses it to cancel eye movements.^[30]

A vessel shows as a dark dip in the brightness profile across it. Its width is measured where the dip is half as deep, like a full width at half maximum.

Simulated video in which the true vessel diameter is known exactly, so the tracker's error can be measured before real recordings exist.

A percentile is the share of the cohort with a lower value. Tertiles cut the cohort into thirds at the 33rd and 67th percentiles; GlaucomAI's phenotype uses them.

How many standard deviations a value lies from a reference mean: 0 is average, beyond ±2 is unusual.

Models the log-odds of disease as a weighted sum of inputs. GlaucomAI's screening model uses age, sex and IOP; coefficients per standard deviation show how strongly each input pulls.

Sensitivity is the share of patients a test flags; specificity is the share of healthy people it clears. Moving the threshold trades one for the other.^[33]

Sensitivity + specificity − 1. The threshold with the highest J is a common default operating point, and the one GlaucomAI's screening model uses.^[34]

Resample the patients with replacement thousands of times and recompute the metric each time; the middle 95% of the results is the interval.^[35]

When several hypotheses are tested, Holm's step-down method keeps the chance of any false positive at 5%. GlaucomAI has one primary question and corrects the rest.^[39]

Splitting data into folds by patient, not by eye, so the two eyes of one person never sit on opposite sides of a train/test split.

Testing a finished model on data from another source: another hospital, camera or population. It is harder than an internal split and closer to real use.^[36]

Replacing names and IDs with study codes, with the key kept separately. Under the GDPR, pseudonymised data is still personal data, which is why the patient pages can be switched off.

A record of every value GlaucomAI excluded or corrected, with the rule and the reason, so each decision can be reviewed and reversed.