Volume of the anterior chamber
Anterior chamber depth: 3.6 mm (Gullstrand model eye)
Anterior chamber volume: 160–200 μL
Aqueous humor turnover time: complete replacement in about 60–70 minutes
The Eye in Numbers — A Reference for Ophthalmic Normal and Standard Values
Key points at a glance
Section titled “Key points at a glance”1. The eye in numbers
Section titled “1. The eye in numbers”This article is a reference that brings together the normal values and threshold values most often used in clinical ophthalmology, organized by anatomical region of the eyeball.
The sources were limited to five Japanese ophthalmology textbooks.
- Ophthalmology, 3rd Edition (Volumes 1 and 2)
- Pediatric Ophthalmology
- Ophthalmology Clinical Qualify: Eye Development and Anatomical Function
- Ophthalmology Clinical Close-Up
2. Eye measurements
Section titled “2. Eye measurements”Basic parameters of the whole eye
Section titled “Basic parameters of the whole eye”- Eyeball volume: 2.8 mL in newborns → 6.7–7.5 mL in adults
- Total refractive power of the eyeball: about 58 D
- Total volume of aqueous humor and vitreous body: about 5 mL (vitreous body 94%, anterior chamber aqueous 5%, posterior chamber aqueous 1%)
- Vitreous body volume: about 4 mL (about 80% of the eyeball)
Axial length
Section titled “Axial length”Axial length is the front-to-back length of the eyeball and is the main factor that determines refractive status.
| Time | Axial length |
|---|---|
| Right after birth | 16–18 mm (about 17 mm) |
| 1 year old | About 21 mm |
| 2–5 years | 22.15 mm |
| 5–16 years | 22.71 mm |
| Adult emmetropic eye | about 24 mm |
Axial length increases rapidly in the first year after birth and reaches a plateau around age 6–7 years. In newborns, the anterior segment reaches 70–80% of the adult size, while the posterior segment remains at 50% or less. The axial length of the Gullstrand schematic eye is defined as 24.0 mm.
Criteria for microphthalmos
Section titled “Criteria for microphthalmos”- Definition of true microphthalmos: eyeball volume is 2/3 or less of normal (axial length is 0.87 or less of the age-normal value)
- Adult microphthalmos threshold: men 20.4 mm or less, women 20.1 mm or less
- Weiss diagnostic criteria (11 years and older): axial length 20.9 mm or less
- Clinical guideline: corneal diameter 10 mm or less (infants 9 mm or less), axial length under 21 mm (19 mm in a 1-year-old child)
The normal values by age and the microphthalmia threshold are shown below (measured by ultrasound A-mode, unit: mm).
| Age | Normal (male) | Normal (female) | Microphthalmia (male) | Microphthalmia (female) |
|---|---|---|---|---|
| After birth | 16.85 | 16.60 | 14.70 | 14.44 |
| 2 years old | 20.60 | 20.29 | 17.97 | 17.65 |
| 6–7 years | 22.00 | 21.68 | 19.19 | 18.86 |
| 13 years to adult | 23.40 | 23.06 | 20.42 | 20.06 |
Q
How much does axial length differ between newborns and adults?
A
Axial length is about 17 mm in newborns and about 24 mm in adults, a difference of about 7 mm. A simple calculation would predict myopia of more than 15 D, but this is offset by a decrease in corneal refractive power and changes in the lens, keeping the eye emmetropic. This is called emmetropization (emmetropization).
3. Corneal Measurements
Section titled “3. Corneal Measurements”
Kolosky TD, Saga AU, Dariano DF III, Das U, Panchal BK, Bregman JA, Levin MR, Alexander JL. Comparison of angle-to-angle distance and corneal diameter in pediatric eyes using ultrasound biomicroscopy. PLoS One. 2024 Jun 18;19(6):e0305624. Figure 1. PMCID: PMC11185497. License: CC BY.
An anterior segment cross-section is shown by ultrasound biomicroscopy, with the measurement points for corneal diameter and angle-to-angle distance marked. You can see at a glance which parts from the corneal edge to the angle are being measured.
Corneal diameter
Section titled “Corneal diameter”-
Adult horizontal diameter: 11–12 mm
-
Adult vertical diameter: 10–11 mm
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Newborn horizontal diameter: 9.8 mm (9–10.5 mm)
-
Newborn vertical diameter: slightly larger, 10.4 mm
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Adult corneal radius of curvature: 7.7–8.0 mm
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Corneal anterior surface radius of curvature in the Gullstrand model eye: 7.7 mm
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Corneal refractive power (Gullstrand model eye): 43.05 D
-
Newborn corneal refractive power: 47.5–51 D (more steeply curved than in adults)
Corneal thickness
Section titled “Corneal thickness”| Layer / location | Thickness |
|---|---|
| Central cornea (adults) | About 520 μm |
| Total corneal thickness (another reported value) | About 550 μm |
| Epithelium | About 50 μm (10% of total thickness) |
| Stroma | About 500 μm (90% of total thickness) |
| Endothelium | About 5 μm |
| Bowman membrane | About 10 μm |
| Peripheral part (adults) | 0.7–0.9 mm |
The thickness ratio of the epithelium : stroma : endothelium is 0.1 : 1 : 0.01.
Corneal thickness in newborns decreases rapidly from 0.96 mm at birth, to 611 μm the next day, and to 580 μm on day 3, reaching the adult level of 0.5 mm by 6 months after birth.
Composition of the corneal stroma
Section titled “Composition of the corneal stroma”- Type I collagen: about 80%
- Type III collagen: about 10%
- Type V collagen: about 5%
- Collagen fiber spacing: about 64 nm
- Corneal stroma water content: 78%
Corneal endothelial cells
Section titled “Corneal endothelial cells”Corneal endothelial cells do not divide or proliferate in the living body and decrease with age.
| Indicator | Value |
|---|---|
| Corneal endothelial cell density at birth | about 5,000 cells/mm² |
| Corneal endothelial cell density in early childhood | 3,500 cells/mm² |
| Corneal endothelial cell density in older adults | 2,500–3,000 cells/mm² |
| Age-related decrease rate | 0.3–0.7% per year (about 0.6%/year) |
| Bullous keratopathy threshold | 500 cells/mm² or less |
The normal area of endothelial cells is about 300 μm², and the thickness is 4–6 μm. For morphologic evaluation, the normal coefficient of variation (CV value) is about 0.25; 0.35 or higher is considered abnormal. The normal hexagonal cell rate is 70–80%, and 50% or less is considered abnormal.
The turnover of corneal epithelial cells is about one week.
Age-related changes
Section titled “Age-related changes”It has not been proven that corneal thickness increases with age. Age-related corneal changes include arcus senilis, vascular ingrowth, and against-the-rule astigmatism.
Q
Why is corneal endothelial cell density important?
A
Corneal endothelial cells maintain the water content of the cornea at a constant level through their pump function and preserve transparency. Because they do not divide in the living eye, they do not recover once they decrease due to aging or surgical trauma. When the count falls to 500 cells/mm² or less, bullous keratopathy develops and the cornea becomes edematous and cloudy.
Anterior segment values
Section titled “Anterior segment values”Sclera
Section titled “Sclera”The sclera makes up about 5/6 of the outer wall of the eyeball. Its thickness varies greatly by location.
| Location | Thickness |
|---|---|
| Around the optic disc (thickest part) | About 1 mm |
| Corneal limbus | 0.8 mm |
| Equatorial region | 0.6 mm |
| Rectus muscle insertion (thinnest part) | 0.3 mm |
In children, the sclera at the equator is 0.45 mm thick, thinner than the 1.09 mm in adults, and in infants and young children it can enlarge easily because of high intraocular pressure (buphthalmos).
The main structures that pass through the sclera are as follows.
- Vortex veins: one in each quadrant, four in total
- Short posterior ciliary arteries and nerves: about 20
- Long posterior ciliary arteries and nerves: two at the horizontal positions of 3 and 9 o’clock
Anterior chamber and aqueous humor
Section titled “Anterior chamber and aqueous humor”Production of aqueous humor
Daytime secretion: about 2.5–3.0 μL/min
Nighttime secretion: about 1.5 μL/min (reduced to about 50% of the awake level)
Active transport: accounts for 80–90% of aqueous humor production
Aqueous humor production decreases by 3.2% every 10 years with age. This is thought to be one reason intraocular pressure in Japanese people decreases with age.
For aqueous humor outflow, the outflow pathway through Schlemm’s canal is the main route and accounts for 90% of total outflow.
Intraocular pressure related
Section titled “Intraocular pressure related”- Corneal stromal swelling pressure: about 50 mmHg
- Imbibition pressure (IP) in healthy eyes: about 35–45 mmHg (negative pressure)
- Thin corneas or flat corneas can cause intraocular pressure to be measured lower
- Non-contact tonometer: values of 18 mmHg or higher should be confirmed with a Goldmann applanation tonometer
Pediatric glaucoma related
Section titled “Pediatric glaucoma related”- Diagnostic criteria for early-onset developmental glaucoma: corneal diameter 12 mm or more, intraocular pressure under sedation 15 mmHg or more
- Even with an intraocular pressure of 15–20 mmHg, consider surgery if the corneal diameter is markedly enlarged
- 60% are diagnosed by 6 months of age, and 80% by 1 year of age
5. Numerical values for the lens, ciliary body, and vitreous body
Section titled “5. Numerical values for the lens, ciliary body, and vitreous body”Of the eye’s total refractive power of about 58 D, the lens contributes about 15–20 D (19.11 D in the Gullstrand schematic eye). The lens continues to enlarge throughout life.
| Age | Lens diameter |
|---|---|
| At birth | 6.00 mm |
| 2 months | 6.80 mm |
| 3 months | 7.1 mm |
| 6–9 months | 7.66 mm |
| 1 year 9 months | 8.4 mm |
| 2–5 years | 8.5 mm |
| 16 years | 9.3 mm |
Lens diameter correlates most strongly with axial length.
Ciliary body
Section titled “Ciliary body”The ciliary muscle consists of three layers: circular muscle (Muller muscle), oblique muscle (radial muscle), and longitudinal muscle (Brucke muscle).
- Posterior end of the ciliary process region (adults): 2–2.5 mm from the corneal limbus
- Posterior edge of the pars plana (ora serrata): nasal side 5 mm, temporal side 7 mm, average 6 mm (from the corneal limbus)
- Width of the pars plana: about 2.5–5.5 mm, measured from the corneal limbus
- Suture pass distance for IOL fixation in the ciliary sulcus: 1.2–2.0 mm from the corneal limbus (ab externo method)
- Anterior ciliary arteries: 1 in the lateral rectus, 2 each in the other three rectus muscles, 7 in total
Vitreous
Section titled “Vitreous”- Vitreous volume: about 4 mL (about 80% of the eye’s total volume)
- Thickness of the vitreous cortex: 100–300 μm
- Location of the vitreous base: 1–2 mm anterior and 2–3 mm posterior to the ora serrata
With age, the vitreous becomes more liquefied. At ages 14–18, about 20% is liquefied overall, and at ages 80–90, more than 50% is liquefied. The peak progression from partial posterior vitreous detachment (PVD) to complete posterior vitreous detachment occurs in the 50s to 60s.
Q
Why is the needle inserted 3.5–4 mm from the corneal limbus for intravitreal injection?
A
Based on the anatomy of the pars plana. To avoid the pars plicata (2 to 2.5 mm from the limbus) and to safely enter anterior to the ora serrata (average 6 mm), the 3.5 to 4.0 mm position is chosen. In phakic eyes, it is placed slightly more posteriorly (4 mm) to avoid contact with the lens.
6. Posterior segment numbers
Section titled “6. Posterior segment numbers”Retina
Section titled “Retina”- Number of rod cells (per eye): about 100 million
- Number of cone cells (per eye): 6 to 7 million
- Disks in the photoreceptor outer segments: 1,000 to 2,000 disks, with about 10% shed and removed each day
- Thickness of the inner limiting membrane: posterior pole 2.5 to 3.5 μm, peripheral retina 1.5 μm
- Start of retinal vascular development: begins at the optic disc at 14 to 15 weeks of gestation and reaches the periphery by the perinatal period
Macula and fovea
Section titled “Macula and fovea”Foveola
Diameter: 300 to 500 μm
Retinal thickness (histology): 0.13 mm
Retinal thickness (optical coherence tomography): 0.18–0.2 mm
Development stage
Start of macula formation: around 7 months of gestation
Completion of the fovea: around 4 months after birth
Maturation of the macula: almost mature by 15 months after birth, with maturation continuing until around age 5
Kishi pocket appears around age 3, the communicating passage with the Cloquet canal can be seen from age 5, and it is present in 50% of cases by age 11.
Choroid
Section titled “Choroid”- Subfoveal choroidal thickness in highly myopic eyes (axial length 26.5 mm or more): about 50 μm
- Greatest factor in choroidal thinning: increased axial length (significantly more than aging or myopia itself)
Optic nerve
Section titled “Optic nerve”The optic nerve is about 50 mm long and is divided into the following four parts.
| Part | Length |
|---|---|
| intraocular | 1 mm |
| intraorbital | 25–30 mm |
| intracanalicular | 4–10 mm (about 6 mm) |
| intracranial | 10 mm |
- Optic disc diameter: about 1.5 mm
- Optic nerve thickness: about 4 mm (about 3 mm behind the eyeball, increasing to about twice that at the posterior lamina cribrosa due to myelination)
- Total number of nerve fibers: 1.0–1.2 million (about 90% are small-diameter fibers)
- Papillomacular fibers: account for about one-third of all nerve fibers
- Distance from the posterior globe to the orbital apex: about 20 mm (the intraorbital optic nerve is 25 mm long, leaving about 5 mm of spare length)
- Point where the central retinal artery enters the optic nerve: about 12 mm behind the globe
- Ciliary ganglion: 1 cm behind the globe, lateral to the optic nerve, 2–3 mm in diameter
- Peak number of optic nerve axons: fetal weeks 16–17 (then decreases and becomes stable around week 29)
- Completion of optic nerve myelination: around age 2 years (progresses from the brain toward the eyeball and stops at the lamina cribrosa)
Q
How many photoreceptors are there in the human retina?
A
Each eye has about 100 million rod cells and 6–7 million cone cells. Rods handle scotopic (dim-light) vision, while cones handle photopic vision and color vision. The outer segment of photoreceptors contains 1,000–2,000 disc membranes, and about 10% are phagocytosed and renewed daily by the retinal pigment epithelium.
7. Numbers for the ocular adnexa and orbit
Section titled “7. Numbers for the ocular adnexa and orbit”Dimensions of the extraocular muscles
Section titled “Dimensions of the extraocular muscles”The muscle length of the four rectus muscles is about 40 mm each, and their insertion distances from the corneal limbus differ (Tillaux’s spiral).
| Extraocular muscles | Tendon length (mm) | Distance from limbus |
|---|---|---|
| Medial rectus (MR) | 3.7 | 5.5 mm |
| Inferior rectus (IR) | 5.5 | 6.5 mm |
| Lateral rectus (LR) | 8.8 | 6.9 mm |
| Superior rectus (SR) | 5.8 | 7.7 mm |
The inferior oblique muscle is 36 mm long (tendon <1 mm), and the superior oblique muscle is 60 mm long (tendon 30 mm).
- Width of insertion of the 4 rectus muscles: about 10 mm (medial rectus 10.3, inferior rectus 9.8, lateral rectus 8.8, superior rectus 10.8)
- Innervation point of the 4 rectus muscles: 26 mm posterior to the insertion
- Distance between the extraocular muscles: about 10 mm
- Tillaux spiral distance: 80 mm
- Levator palpebrae superioris: muscle portion about 40 mm, tendon portion 14–20 mm
- Course and action of the rectus muscles: maximum elevation/depression at 23° of abduction, maximum rotation at 67° of adduction
- Action of the oblique muscles: maximum rotation at 39° of abduction, maximum elevation/depression at 51° of adduction
- Medial wall of the orbit (ethmoid bone, lacrimal bone, maxilla, lesser wing of the sphenoid bone): the thinnest among the four walls
- The optic canal begins about 6 mm posterior to the posterior ethmoidal foramen
- There is a trochlea 4 mm deep to the nasal side of the orbital rim
- Orbital volume increases with growth
Eyelids
Section titled “Eyelids”- Upper eyelid margin to corneal light reflex distance (MRD1): usually 5.0–5.5 mm
- Width of the lower eyelid margin covering the lower limbus: usually 2.0 mm
- Meibomian gland openings: 25–40 in the upper eyelid, 20–30 in the lower eyelid
Tear fluid and tear drainage
Section titled “Tear fluid and tear drainage”Tear fluid is a thin fluid layer essential for protecting the ocular surface and maintaining optical quality.
- Tear film thickness: about 3–7 μm
- Distribution of tear fluid: ocular surface tear film 1.1 μL, tear meniscus 2.9 μL (75% of exposed tear fluid), conjunctival sac 4.5 μL
- Tear secretion rate: 1–2 μL per minute
- Drainage route: 90% drains through the puncta, 10% evaporates from the ocular surface
The dimensions of the tear drainage system are as follows.
- Lacrimal punctum (lacrimal canalicular papilla/stenotic segment): about 1 mm
- Vertical part of the lacrimal canaliculus: about 1.4 mm
- Horizontal part of the lacrimal canaliculus: about 10 mm
- Common canaliculus: about 2 mm
- Length of the lacrimal sac: 15 mm (from the common canaliculus to the dome, 5 mm; from the common canaliculus to the nasolacrimal duct junction, 10 mm)
- Length of the membranous nasolacrimal duct: 17 mm
- The epithelium of the lacrimal sac and nasolacrimal duct absorbs 90% of tears
8. Eye development in children
Section titled “8. Eye development in children”Visual development
Section titled “Visual development”| Development indicator | Time/value |
|---|---|
| Newborn refractive value (1 month) | Average +3.2 D |
| Refractive value at 3 months of age | Average +3.9 D |
| Refractive value at 1 year of age | Average +1.9 D |
| Peak visual sensitivity | Around 18 months of age (remains until age 8) |
| Completion of normal binocular vision | 2 to 6 months after birth |
| Development of stereopsis | Until around 24 months of age |
| Confirmation of color vision | A few at 4 weeks, all by 12 weeks |
In newborns, hyperopia increases until 3 months after birth (+3.2 D → +3.9 D), then starts to decrease and emmetropization progresses.
Within 4 weeks of birth, most newborns have straight eye alignment, while the others show small-angle exotropia. By 4 months, eye alignment becomes straight and convergence is good. The binocular visual field in infants develops gradually from immediately after birth to 7 weeks, then expands rapidly from 2 months to 6–8 months after birth.
Timing of development of each tissue
Section titled “Timing of development of each tissue”| Tissue/structure | Developmental timing |
|---|---|
| Formation of the anterior chamber angle | Embryonic 10–12 weeks |
| Appearance of Schlemm’s canal | Embryonic 16 weeks |
| Completion of the angle | Around the 8th month of gestation |
| Start of corneal endothelial differentiation | Embryonic 8–10 weeks |
| Completion of the corneal endothelium monolayer | 15–20 weeks of gestation |
| Start of macular formation | Around 7 months of gestation |
| Completion of the fovea | Around 4 months after birth |
| Start of retinal blood vessel development | 14–15 weeks of gestation |
| Development of the extraocular muscles | 4 weeks of gestation |
| Development of the lacrimal gland | 7 weeks of gestation |
| Start of secretion from the lacrimal gland | 3 months of embryonic development |
| Completion of myelination of the optic nerve | Around age 2 |
Myelination of the optic nerve progresses from the brain toward the eyeball and stops at the lamina cribrosa. Development of the lacrimal gland continues through infancy.
References
Section titled “References”- Atchison DA, Thibos LN. Optical models of the human eye. Clin Exp Optom. 2016;99(2):99-106. PMID: 26969304.
- Pakravan M, Alvani A, Esfandiari H, Ghahari E, Yaseri M. Post-trabeculectomy ocular biometric changes. Clin Exp Optom. 2017;100(2):128-132. PMID: 27686794.
- He M, Chen H, Wang W. Refractive Errors, Ocular Biometry and Diabetic Retinopathy: A Comprehensive Review. Curr Eye Res. 2021;46(2):151-158. PMID: 32589053.