Choroidal Thickness: Normal Values, OCT Measurement, Changes in Myopia, Glaucoma, and Eye Diseases

Title: Choroidal Thickness: Normal Values, OCT Measurement, Myopia & Glaucoma

Description: Learn about choroidal thickness, normal values, OCT measurement, factors affecting thickness, and changes associated with myopia, glaucoma, age, and other eye diseases.

Focus Keyword: Choroidal thickness

Secondary Keywords: choroidal thickness OCT, normal choroidal thickness, choroid thickness in myopia, choroidal thickness in glaucoma, OCT choroid measurement, choroidal thickness changes

Introduction

Choroidal thickness is an important structural parameter used in modern ophthalmology and optometry to evaluate the health of the posterior segment of the eye.

The choroid is the vascular layer located between the retina and sclera. It contains a dense network of blood vessels that provides oxygen and nutrients to the outer retina, particularly the retinal pigment epithelium (RPE) and photoreceptors.

With the development of Optical Coherence Tomography (OCT), clinicians can measure choroidal thickness noninvasively and assess changes associated with different ocular conditions.

Choroidal thickness can vary considerably between individuals and is influenced by:

• Age
• Axial length
• Refractive error
• Myopia
• Hyperopia
• Glaucoma
• Diurnal variation
• Systemic factors
• Ocular diseases

Understanding choroidal thickness is particularly important when studying myopia, glaucoma, age-related macular degeneration, central serous chorioretinopathy, and other retinal or choroidal disorders.

What Is Choroidal Thickness?

Choroidal thickness refers to the vertical distance between the outer boundary of the retinal pigment epithelium/Bruch's membrane complex and the inner surface of the sclera on OCT imaging.

In simple terms:

RPE–Bruch's membrane complex

↓

Choroid

↓

Sclera

The distance between the upper and lower boundaries of the choroid represents its thickness.

Why Is Choroidal Thickness Important?

The choroid has an important physiological relationship with the retina.

It provides:

• Oxygen
• Nutrients
• Blood supply
• Metabolic support
• Heat regulation
• Waste removal

Therefore, changes in choroidal structure may provide information about the underlying health of the posterior eye.

However, choroidal thickness is not a direct measurement of choroidal blood flow or function. A thicker choroid does not necessarily mean better circulation, and a thinner choroid does not automatically mean disease.

Normal Choroidal Thickness

There is no single normal choroidal thickness value that applies to every person.

Choroidal thickness varies between individuals and depends on several factors.

Many OCT studies report average subfoveal choroidal thickness (SFCT) values in the general adult population roughly in the 200–300 µm range, but published values vary substantially depending on the population, OCT device, measurement technique, age, and refractive characteristics.

Therefore, a value should always be interpreted in clinical context rather than using one universal cutoff.

Important point

Normal choroidal thickness is a range, not one fixed number.

What Is Subfoveal Choroidal Thickness?

Subfoveal choroidal thickness (SFCT) is the thickness of the choroid directly beneath the foveal center.

It is one of the most commonly reported choroidal measurements in clinical research.

The measurement is taken from:

Outer boundary of RPE/Bruch's membrane complex → Inner scleral boundary

How Is Choroidal Thickness Measured?

The most common method is Optical Coherence Tomography (OCT).

OCT uses low-coherence light to produce high-resolution cross-sectional images of ocular tissues.

For better visualization of the choroid, clinicians may use:

• Enhanced Depth Imaging OCT
• Swept-Source OCT
• High-resolution OCT

Enhanced Depth Imaging OCT

Enhanced Depth Imaging (EDI-OCT) improves visualization of deeper structures, including the choroid and sclera.

It allows clinicians to obtain clearer images of:

• Choroidal vessels
• Choroidal stroma
• Choriocapillaris
• Scleral boundary

This makes EDI-OCT particularly useful when studying choroidal thickness.

Swept-Source OCT

Swept-Source OCT (SS-OCT) uses longer wavelengths than conventional spectral-domain OCT and can provide better penetration into deeper ocular tissues.

It can be particularly useful for evaluating:

• Thick choroids
• Highly myopic eyes
• Posterior staphyloma
• Choroidal lesions
• Scleral structures

Step-by-Step Measurement of Choroidal Thickness

Step 1: Obtain a high-quality OCT scan

The patient fixates on a target while the OCT captures cross-sectional retinal images.

Step 2: Identify the fovea

The foveal center is located on the OCT scan.

Step 3: Identify the RPE-Bruch's membrane complex

This provides the upper boundary of the choroid.

Step 4: Identify the scleral interface

The inner surface of the sclera forms the lower boundary.

Step 5: Measure the perpendicular distance

The distance between these boundaries represents the choroidal thickness.

Different Ways to Measure Choroidal Thickness

Choroidal thickness can be measured at different retinal locations.

1. Subfoveal Measurement

Directly beneath the fovea.

2. Parafoveal Measurement

Measurements are taken at specified distances from the foveal center.

3. Peripapillary Measurement

Choroidal thickness is measured around the optic nerve.

4. Choroidal Thickness Maps

Modern OCT software can generate maps showing regional variation in choroidal thickness.

Factors Affecting Choroidal Thickness

Choroidal thickness is highly variable.

1. Age

One of the most consistent factors associated with choroidal thickness is age.

In general, the choroid tends to become thinner with increasing age, although the magnitude of change varies between individuals.

2. Axial Length

Longer axial length is commonly associated with a thinner choroid.

This is particularly important in high myopia.

3. Refractive Error

Refractive status influences choroidal thickness.

Generally:

Higher myopia → thinner choroid

while hyperopic eyes may have relatively thicker choroids.

4. Diurnal Variation

Choroidal thickness can change during the day.

Therefore, the timing of OCT measurements can affect measurements.

This is particularly important in research studies where repeated measurements are compared.

5. Age and Ocular Biometry

Other variables such as:

• Axial length
• Anterior chamber parameters
• Refractive error

can influence the measured choroidal thickness.

Choroidal Thickness in Myopia

One of the most widely studied relationships is between myopia and choroidal thickness.

As myopia increases, particularly in eyes with increased axial length, the choroid often becomes progressively thinner.

The simplified relationship is:

Axial elongation

↓

Choroidal stretching/thinning

↓

Reduced choroidal thickness

This is especially important in pathologic myopia.

Why Does the Choroid Become Thin in Myopia?

The exact mechanisms are complex.

As the eye elongates, several posterior ocular structures undergo remodeling and stretching.

This can result in:

• Choroidal thinning
• Scleral changes
• Retinal stretching
• RPE alterations

In severe myopia, these changes can contribute to degenerative complications.

Choroidal Thickness in High Myopia

High myopia can be associated with marked choroidal thinning.

Associated findings may include:

• Patchy chorioretinal atrophy
• Lacquer cracks
• Posterior staphyloma
• Myopic macular degeneration
• Choroidal neovascularization

Choroidal Thickness and Myopia Progression

The relationship between choroidal thickness and myopia progression is an active area of research.

In children and adolescents, changes in choroidal thickness can occur during periods of axial elongation.

However, choroidal thickness alone should not be used to diagnose or predict myopia progression in an individual patient.

Axial length, refraction, age, family history, and other clinical factors are also important.

Choroidal Thickness in Glaucoma

The relationship between choroidal thickness and glaucoma is more complex.

Some studies have reported differences in choroidal thickness in glaucoma patients, while other studies have found inconsistent or modest associations.

Possible mechanisms being investigated include:

• Altered ocular blood flow
• Vascular factors
• Age-related thinning
• Changes in ocular biomechanics
• Association with axial length

Important clinical point

Choroidal thickness is not currently a standalone diagnostic test for glaucoma.

Glaucoma diagnosis primarily depends on:

• Optic nerve assessment
• Retinal nerve fiber layer analysis
• Ganglion cell analysis
• Intraocular pressure
• Visual field testing
• Clinical examination

Choroidal Thickness and Glaucoma Progression

Research continues to investigate whether choroidal measurements may provide additional information about glaucoma progression.

The choroid is involved in ocular blood supply, so vascular changes could theoretically influence optic nerve health.

However, the relationship is not simple enough to use choroidal thickness alone for diagnosis or progression monitoring.

Choroidal Thickness in Age-Related Macular Degeneration

Changes in the choroid and choriocapillaris are important in age-related macular degeneration (AMD).

Some patients with AMD show choroidal thinning, although choroidal changes vary according to disease subtype and stage.

Changes may involve:

• Choriocapillaris
• RPE
• Bruch's membrane
• Choroidal vessels

Choroidal Thickness in Central Serous Chorioretinopathy

Central Serous Chorioretinopathy (CSC) is strongly associated with abnormalities of the choroid.

Many patients with CSC demonstrate a thickened choroid, often described within the pachychoroid spectrum.

Common findings include:

• Increased choroidal thickness
• Dilated outer choroidal vessels
• Choroidal hyperpermeability
• RPE abnormalities
• Subretinal fluid

What Is Pachychoroid?

Pachychoroid refers to a group of conditions characterized by structural abnormalities of the choroid, often including increased choroidal thickness and dilation of larger choroidal vessels.

The term is commonly associated with the pachychoroid spectrum.

Conditions may include:

• Pachychoroid pigment epitheliopathy
• Central serous chorioretinopathy
• Pachychoroid neovasculopathy

Choroidal Thickness in Diabetic Eye Disease

Diabetes can affect both retinal and choroidal circulation.

Studies have reported variable changes in choroidal thickness among patients with diabetes and diabetic retinopathy.

Potential factors include:

• Microvascular damage
• Altered blood flow
• Retinal disease severity
• Duration of diabetes
• Systemic vascular factors

Because findings are variable, choroidal thickness should be interpreted alongside retinal findings and systemic history.

Choroidal Thickness in Inflammatory Eye Disease

Inflammatory conditions involving the choroid can produce structural changes.

Examples include:

• Posterior uveitis
• Choroiditis
• Vogt-Koyanagi-Harada disease
• Other inflammatory chorioretinal disorders

For example, acute inflammatory disease can produce significant choroidal thickening, while chronic disease may result in thinning in some cases.

Choroidal Thickness in Vogt-Koyanagi-Harada Disease

Vogt-Koyanagi-Harada (VKH) disease is an inflammatory disorder that can produce substantial choroidal thickening.

OCT may show:

• Marked choroidal thickening
• Serous retinal detachments
• RPE changes
• Inflammatory alterations

Choroidal thickness can decrease substantially after appropriate treatment, making OCT useful for monitoring disease activity in conjunction with clinical findings.

Choroidal Thickness in Uveitis

Inflammation can alter choroidal thickness.

Depending on the disease and stage:

Active inflammation → possible choroidal thickening

Chronic damage → possible choroidal thinning

The exact pattern varies by disease.

Choroidal Thickness and Age

Age is an important factor when interpreting OCT.

As age increases, the choroid generally becomes thinner.

Therefore, comparing a young patient's choroidal thickness with an elderly patient's value without considering age may be misleading.

Choroidal Thickness and Sex

Some studies have reported differences in choroidal thickness between males and females.

However, sex-related differences are generally less important clinically than factors such as:

• Age
• Axial length
• Refractive error
• Measurement technique

Choroidal Thickness and Axial Length

Axial length is particularly important when interpreting choroidal thickness.

A long eye, commonly seen in high myopia, tends to have a thinner choroid.

Therefore, two patients with identical choroidal thickness values may have different clinical interpretations depending on their axial length.

Choroidal Thickness and Blood Flow

It is important to distinguish between:

Choroidal Thickness

A structural measurement obtained using OCT.

Choroidal Blood Flow

A physiological measurement describing blood circulation through the choroidal vascular network.

These are related but not equivalent.

Thicker choroid ≠ automatically better blood flow

Thinner choroid ≠ automatically poor blood flow

This is an important clinical and examination concept.

Choroidal Thickness Measurement Errors

OCT measurements can be affected by several factors.

1. Poor Image Quality

Low-quality scans can make the scleral boundary difficult to identify.

2. Incorrect Foveal Localization

Measuring away from the true foveal center can produce different values.

3. Segmentation Errors

Automated software may incorrectly identify tissue boundaries.

4. Device Differences

Different OCT machines can produce different measurements.

5. Manual Measurement Variability

Two observers may identify the scleral boundary differently.

Automated vs Manual Choroidal Thickness Measurement

Modern OCT devices often use automated segmentation.

Advantages

• Fast
• Reproducible
• Suitable for large datasets

Limitations

• Segmentation errors
• Difficulty identifying the scleral boundary
• Reduced accuracy in abnormal eyes

Manual correction may be necessary when automated segmentation is inaccurate.

Choroidal Thickness Maps

Instead of measuring one point, clinicians can evaluate the choroid across multiple locations.

This can identify:

• Regional thickening
• Regional thinning
• Asymmetry
• Disease-associated patterns

Why Choroidal Thickness Is Not a Standalone Diagnostic Test

Although choroidal thickness is clinically useful, it should not be interpreted in isolation.

A patient's OCT should be considered alongside:

• Visual acuity
• Refraction
• Axial length
• Intraocular pressure
• Fundus examination
• OCT retinal findings
• Visual field
• Symptoms
• Medical history

This is especially important because a value that is abnormal for one patient may be normal for another.

Clinical Applications of Choroidal Thickness

Choroidal thickness measurements can be useful for:

Myopia

Monitoring structural changes associated with axial elongation.

CSC

Identifying choroidal thickening and monitoring changes.

Inflammatory diseases

Assessing choroidal inflammation and response to treatment.

AMD

Studying choroidal and choriocapillaris alterations.

Glaucoma research

Investigating relationships between choroidal structure and optic nerve disease.

Research

Understanding ocular growth, vascular function, and disease mechanisms.

Choroidal Thickness: Thick vs Thin

Thick ChoroidThin ChoroidCSC/pachychoroid spectrumHigh myopiaSome inflammatory diseasesIncreasing ageVKH during active inflammationPathologic myopiaSome pachychoroid disordersSome degenerative conditionsMay occur transientlyMay reflect chronic structural change

Important: These are associations, not diagnostic rules. Choroidal thickness must be interpreted in context.

Normal vs Abnormal Choroidal Thickness

There is no universal cutoff separating normal from abnormal choroidal thickness.

A clinically meaningful interpretation should consider:

• Age
• Axial length
• Refractive error
• OCT device
• Measurement location
• Disease status
• Previous measurements

Serial measurements in the same patient using the same technique can often be more informative than comparing a single number with a population average.

Can Choroidal Thickness Predict Eye Disease?

Choroidal thickness can provide useful structural information, but it generally cannot predict disease by itself.

For example:

Thin choroid ≠ automatically glaucoma

Thin choroid ≠ automatically pathological myopia

Thick choroid ≠ automatically CSC

The complete clinical picture matters.

Frequently Asked Questions

What is normal choroidal thickness?

There is no single universal normal value. In many adult OCT studies, average subfoveal choroidal thickness is roughly in the 200–300 µm range, but considerable variation exists.

How is choroidal thickness measured?

It is most commonly measured using OCT, particularly EDI-OCT or swept-source OCT.

What is subfoveal choroidal thickness?

It is the thickness of the choroid directly beneath the center of the fovea.

Does myopia make the choroid thinner?

Generally, increasing myopia and axial elongation are associated with reduced choroidal thickness, particularly in high myopia.

Is choroidal thickness reduced in glaucoma?

Some studies have reported thinner choroids in glaucoma, but the relationship is inconsistent. Choroidal thickness is not a standalone diagnostic test for glaucoma.

Which disease is associated with a thick choroid?

Central serous chorioretinopathy and other pachychoroid-spectrum disorders are commonly associated with increased choroidal thickness.

Does age affect choroidal thickness?

Yes. The choroid generally becomes thinner with increasing age.

Does choroidal thickness change during the day?

Yes. Diurnal variation can occur, which is important when comparing repeated measurements.

Can OCT measure choroidal thickness?

Yes. OCT is the standard noninvasive imaging method used to assess choroidal thickness.

Is a thin choroid always abnormal?

No. A thin choroid can be associated with normal aging, long axial length, myopia, and other factors. Clinical context is essential.

Easy Mnemonics

Myopia → Thin

Think:

“MYO = Minus → Choroid gets More Thin.”

So:

More myopia → thinner choroid

CSC → Thick

Think:

“Serous = Swollen.”

CSC is commonly associated with:

Thick choroid + hyperpermeability + subretinal fluid

OCT Boundaries

Remember:

RPE → Choroid → Sclera

The distance between RPE/Bruch's membrane and sclera = choroidal thickness.

Conclusion

Choroidal thickness is an important OCT-derived measurement that provides valuable information about the structure of the posterior eye. It is particularly useful in the study of myopia, central serous chorioretinopathy, inflammatory diseases, age-related macular degeneration, and other chorioretinal disorders.

There is no single universal normal choroidal thickness value. Measurements vary according to age, axial length, refractive error, location, time of day, OCT technology, and measurement technique. In many adult populations, subfoveal values commonly fall around 200–300 µm, but this should not be treated as a universal normal range.

The most important clinical associations to remember are:

Myopia → generally thinner choroid

Aging → generally thinner choroid

CSC/pachychoroid → often thicker choroid

Inflammation → can cause choroidal thickening

Glaucoma → association is complex and not diagnostic

For accurate interpretation, choroidal thickness should always be evaluated together with OCT retinal findings, axial length, refractive status, age, fundus examination, visual function, and the patient's clinical history.