Ophthalmic Normal Values: Quick Reference for the Eye Clinic
Last updated: October 2026
The numbers we check every day, on one page. Values are typical adult ranges; always interpret them against age, ethnicity, the device used and the fellow eye.
Globe, cornea and anterior segment
| Parameter | Typical normal | Notes and red flags |
|---|---|---|
| IOP (Goldmann) | 10–21 mmHg (mean about 15–16) | Inter-eye difference over 3–4 mmHg needs attention. Read with CCT. See CCT and IOP. |
| Central corneal thickness | About 520–560 µm (mean about 540) | Under 500 µm: IOP underestimated and caution for refractive surgery. Thick in Fuchs dystrophy and corneal oedema. |
| Keratometry (mean K) | About 42–45 D (range 40–48) | Over 47–48 D, or asymmetry over 1 D between eyes: think keratoconus. See the topography card. |
| Corneal astigmatism | Under 1 D in most eyes | With-the-rule in the young, drifting to against-the-rule with age |
| Horizontal corneal diameter (white-to-white) | Adult 11.5–12.5 mm; newborn about 10 mm | Over 12 mm in an infant: rule out congenital glaucoma. Under 10 mm in an adult: microcornea. Over 13 mm: megalocornea. |
| Anterior chamber depth (endothelium to lens) | About 2.8–3.5 mm | Under 2.5 mm: angle-closure risk; check gonioscopy |
| Axial length | About 22.0–24.5 mm (mean 23.5) | Under 22 mm short; over 26 mm long. Inter-eye difference over 0.3 mm: recheck biometry. |
| Lens thickness | About 3.5–5.0 mm, increasing with age | A thick lens with a shallow AC means lens-related angle closure |
| Endothelial cell density | About 2,000–3,000 cells/mm² in adults | See the specular microscopy card |
Tear film and ocular surface
| Test | Normal | Abnormal |
|---|---|---|
| Schirmer I (no anaesthesia, 5 min) | 10 mm or more | Under 5 mm: aqueous deficiency |
| Schirmer with anaesthesia (basal) | Over 5–10 mm | Under 5 mm |
| Tear break-up time (fluorescein or non-invasive) | 10 seconds or more | Under 10 s (DEWS III uses NIBUT under 10 s) |
| Tear osmolarity | Under 308 mOsm/L | 308 or more, or inter-eye difference over 8. See TFOS DEWS III. |
| Tear meniscus height | About 0.2–0.3 mm or more | Under 0.2 mm suggests low tear volume |
Lids and orbit
| Parameter | Normal | Notes |
|---|---|---|
| Palpebral fissure height | About 8–11 mm | |
| MRD1 | About 4–5 mm | 2 mm or less: significant ptosis. See ptosis tests. |
| MRD2 | About 5 mm | Increased in lower-lid retraction (thyroid eye disease) |
| Levator function | 13–15 mm or more | Good 8 mm or more, fair 5–7 mm, poor 4 mm or less |
| Upper lid crease height | About 8–10 mm (lower in many Asian lids) | High crease: aponeurotic ptosis; absent: congenital ptosis |
| Exophthalmometry (Hertel) | About 12–20 mm (population-dependent) | Inter-eye asymmetry of 2 mm or more is significant |
Binocular vision and accommodation
| Parameter | Normal | Notes |
|---|---|---|
| Amplitude of accommodation | Hofstetter: minimum = 15 − 0.25 × age; average = 18.5 − 0.3 × age (D) | Below the minimum for age: accommodative insufficiency |
| Near point of convergence | Up to about 6–8 cm | Over 10 cm: convergence insufficiency |
| AC/A ratio | 3–5 PD per dioptre | High in convergence excess and accommodative esotropia |
| Stereoacuity | 40–60 seconds of arc or better (adults) | Reduced in amblyopia and strabismus |
| Fusional convergence at distance / near | About 14–20 PD / about 25–38 PD (base-out) | Lab and method-dependent |
Optic disc, retina and imaging
| Parameter | Normal | Notes |
|---|---|---|
| Vertical cup-to-disc ratio | Average about 0.3; up to 0.5–0.6 can be normal in large discs | Inter-eye asymmetry over 0.2 is a red flag. Always judge with disc size (DDLS). |
| Disc diameter (vertical) | About 1.5–2.0 mm | Small discs hide cupping; large discs show physiological cups |
| Retinal artery-to-vein calibre | About 2:3 | Arteriolar narrowing in hypertension |
| Central subfield thickness (OCT) | Device-dependent: about 250–270 µm on Cirrus, 270–300 µm on Spectralis | See the OCT macula card |
| Average RNFL thickness (OCT) | About 90–105 µm (device and age dependent) | See the OCT disc card |
| EOG Arden ratio | About 1.8 or more (lab-specific) | Reduced in Best disease. See the electrophysiology card. |
| Pattern VEP P100 latency | About 100 ms (lab upper limit usually around 110–118 ms) | Delayed in demyelination |
Volumes and physiology (viva favourites)
- Aqueous production: about 2–3 µL/min. Anterior chamber volume about 0.25 mL; posterior chamber about 0.06 mL.
- Vitreous volume: about 4 mL. Tear volume: about 7 µL; a drop is about 30–50 µL, so one drop is plenty.
- Episcleral venous pressure: about 8–10 mmHg.
- Normal pupil: 2–4 mm in light; physiological anisocoria up to about 1 mm in up to 20% of people.
How to use this card: normal ranges overlap with disease. A value inside the range can still be abnormal for that patient (for example a CCT of 520 µm that was 560 µm before LASIK), and a value outside it can be normal. Compare with the fellow eye and with previous readings.
Key sources
- AAO Basic and Clinical Science Course (BCSC), current edition: sections on fundamentals, cornea, glaucoma and oculoplastics
- Hofstetter HW. Useful age-amplitude formula. Optom World 1950;38:42–5
- TFOS DEWS III diagnostic cut-offs (Review of Optometry)
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