How is choroidal thickness defined on OCT?

From the internal limiting membrane to the RPE

From Bruch's membrane to Haller's layer

From the outer nuclear layer to the sclera

How does enhanced depth imaging OCT bring the choroid into view?

The device is placed so the choroid sits near the zero delay line With EDI the device is placed close to the eye so the choroid sits near the zero delay line, raising sensitivity in deeper layers on standard spectral-domain machines.

A longer wavelength light source is used

An intravenous contrast dye is injected

Adaptive optics correct the ocular aberrations

How should a choroidal thickness value be used in treatment decisions?

As an adjunct to fluid, angiography and symptoms Thickness supports diagnosis and tracks disease, but treatment should never be started on a thickness value alone; combine it with fluid, angiography and symptoms.

As the sole trigger to start treatment

Only after conversion to axial length units

In place of angiography when fluid is absent

By roughly how much does the choroid thin with each year of age?

About 1.5 micrometers The choroid thins by about 1.5 micrometers each year of age and also thins with each diopter of myopia, so age- and refraction-matched data are needed.

Subfoveal choroidal thickness in pachychoroid disease often exceeds which value?

350 micrometers Thick choroid with dilated large vessels defines the pachychoroid spectrum, and thickness often exceeds 350 micrometers in affected eyes.

Which conditions are associated with a thin choroid on EDI-OCT?

Geographic atrophy and pathologic myopia Eyes with geographic atrophy and pathologic myopia show a thin choroid, and the thinning may precede visible atrophy.

Central serous chorioretinopathy and polypoidal vasculopathy

Acute Vogt-Koyanagi-Harada disease

How does acute Vogt-Koyanagi-Harada disease affect choroidal thickness?

It thickens the choroid, and steroids reduce it Choroiditis such as VKH thickens the choroid in the acute phase, steroid treatment reduces the thickness, and serial scans track recovery and warn of relapse.

It thins the choroid until steroids are started

It leaves choroidal thickness unchanged

It thins the choroid permanently from onset

What does the choroidal vascularity index measure?

Vessel area as a ratio of total choroid area The choroidal vascularity index is the ratio of vessel area to total choroid area on binarized images, and it is less sensitive to age and refraction than thickness.

Choroidal thickness divided by axial length

Percentage of choriocapillaris flow deficits

Ratio of Haller to Sattler layer thickness

Why should serial choroidal thickness scans be taken at the same time of day?

Choroidal thickness changes through the day Brown and colleagues showed diurnal change in choroidal thickness, and caffeine, water intake and exercise can alter it, so repeat scans at the same time of day.

Pupil size alters scan segmentation

Axial length changes after meals

Lens thickness varies with accommodation

Choroidal Thickness on EDI-OCT: Measurement

Choroidal thickness is the distance from the outer border of the retinal pigment epithelium to the chorioscleral interface.

Enhanced depth imaging OCT made this measurement routine.

Therefore, clinicians can now follow the choroid in many diseases.

Why Measure Choroidal Thickness

The choroid supplies the outer retina and shapes many diseases.

Thickening and thinning mark different disease groups.

Also, treatment can change the thickness.

As a result, the measure adds to the diagnosis and follow-up.

Enhanced Depth Imaging

Spaide and colleagues described enhanced depth imaging in 2008.

The device is placed close to the eye so that the choroid sits near the zero delay line.

Also, the technique increases sensitivity in the deeper layers.

Therefore, standard spectral-domain machines can show the choroid.

Test your knowledge 10 questions from this article

Swept-Source OCT

Swept-source devices use a longer wavelength that penetrates deeper.

They image the choroid and the sclera without special settings.

Also, the signal is stronger through cataract and blood.

As a result, many centers now prefer swept-source scans.

Measuring Subfoveal Choroidal Thickness

Place a caliper at the outer border of the pigment epithelium and drag it to the inner scleral border.

Take the measurement under the center of the fovea.

Also, repeat at points 500 and 1,000 micrometers nasal and temporal.

Therefore, report the subfoveal value and the location.

Normal Choroidal Thickness Values

Margolis and Spaide found a mean subfoveal thickness of about 287 micrometers in normal eyes.

Values fall with age and with axial length.

Also, the range is wide among healthy people.

As a result, use age- and refraction-matched reference data.

Effect of Age and Myopia on Choroidal Thickness

The choroid thins by about 1.5 micrometers each year of age.

It also thins with each diopter of myopia.

Also, high myopia can reduce thickness to under 100 micrometers (see tessellated fundus).

Therefore, interpret thickness in context.

Diurnal and Other Variations

Brown and colleagues showed that thickness changes through the day.

The choroid is thickest in the morning and thinner in the evening.

Also, caffeine, water intake and exercise can alter it.

In addition, schedule repeat scans at the same time of day.

Pachychoroid Disease

Thick choroid with dilated large vessels defines the pachychoroid spectrum.

Central serous chorioretinopathy, pachychoroid neovasculopathy and polypoidal vasculopathy are in the group.

Also, thickness often exceeds 350 micrometers in affected eyes.

Therefore, a thick choroid should prompt a search for these diseases.

Thin Choroid in AMD and Myopia

Eyes with geographic atrophy and pathologic myopia show thin choroid.

The thinning may precede visible atrophy.

Also, thin choroid predicts poor response in some diseases.

As a result, thinness serves as a marker of risk.

Choroidal Thickness on EDI-OCT: Measurement and Meaning

Inflammatory Disease

Choroiditis such as Vogt-Koyanagi-Harada disease thickens the choroid in the acute phase.

Treatment with steroids reduces the thickness.

Also, serial scans help to track recovery.

In addition, thickness can warn of relapse.

Choroidal Vascularity Index

Agrawal and colleagues proposed the ratio of vessel area to total choroid area.

It separates vessels from stroma in binarized images.

Also, it is less sensitive to age and refraction than thickness.

Therefore, it adds a second measure of choroidal status.

Choroidal Thickness After Treatment

Photodynamic therapy thins the choroid in central serous disease.

Anti-VEGF therapy can reduce thickness in some eyes.

Also, mineralocorticoid antagonists may thin it in selected patients.

As a result, thickness tracks a response.

Pitfalls in Measuring Choroidal Thickness

The outer border can be hard to see in thick or thin choroid.

Shadowing from pigment or hemorrhage blurs the line.

Also, manual caliper errors affect small changes.

Therefore, use the same observer and the same method.

Automated Segmentation

Software can segment the choroid and give maps.

Errors occur in eyes with disease, so review the lines.

Also, maps allow comparison across the macula.

In addition, report the device and software version.

Clinical Use Today

Use thickness to support a diagnosis and to track disease.

Do not treat on a thickness value alone.

Also, combine it with fluid, angiography and symptoms.

As a result, the measure serves as an adjunct.

Pitfalls to Avoid

Do not compare values between devices without correction
Never interpret thickness without age and refraction
Do not forget the time of day in serial scans
Never use thickness alone to start treatment

Reporting Choroidal Measurements

State the device, the scan mode and the point of measurement.

Give the date and time of the scan.

Also, include age and refraction.

Therefore, others can compare your numbers with yours.

For the latest studies, see the PubMed results for choroidal thickness.

References

Spaide RF, Koizumi H, Pozzoni MC. Enhanced depth imaging spectral-domain optical coherence tomography. Am J Ophthalmol. 2008;146:496-500.
Margolis R, Spaide RF. A pilot study of enhanced depth imaging optical coherence tomography of the choroid in normal eyes. Am J Ophthalmol. 2009;147:811-815.
Brown JS, Flitcroft DI, Ying GS, et al. In vivo human choroidal thickness measurements: evidence for diurnal fluctuations. Invest Ophthalmol Vis Sci. 2009;50:5-12.
Agrawal R, Gupta P, Tan KA, Cheung CM, Wong TY, Cheng CY. Choroidal vascularity index as a measure of vascular status of the choroid: measurements in healthy eyes from a population-based study. Sci Rep. 2016;6:21090.

Test yourself

A few questions straight from this article.

1 / 10 0 correct

How is choroidal thickness defined on OCT?
Choroidal thickness is the distance from the outer border of the retinal pigment epithelium to the chorioscleral interface.
How does enhanced depth imaging OCT bring the choroid into view?
With EDI the device is placed close to the eye so the choroid sits near the zero delay line, raising sensitivity in deeper layers on standard spectral-domain machines.
How should a choroidal thickness value be used in treatment decisions?
Thickness supports diagnosis and tracks disease, but treatment should never be started on a thickness value alone; combine it with fluid, angiography and symptoms.
What mean subfoveal choroidal thickness did Margolis and Spaide find in normal eyes?
Margolis and Spaide found a mean subfoveal thickness of about 287 micrometers in normal eyes, with a wide healthy range.
By roughly how much does the choroid thin with each year of age?
The choroid thins by about 1.5 micrometers each year of age and also thins with each diopter of myopia, so age- and refraction-matched data are needed.
Subfoveal choroidal thickness in pachychoroid disease often exceeds which value?
Thick choroid with dilated large vessels defines the pachychoroid spectrum, and thickness often exceeds 350 micrometers in affected eyes.
Which conditions are associated with a thin choroid on EDI-OCT?
Eyes with geographic atrophy and pathologic myopia show a thin choroid, and the thinning may precede visible atrophy.
How does acute Vogt-Koyanagi-Harada disease affect choroidal thickness?
Choroiditis such as VKH thickens the choroid in the acute phase, steroid treatment reduces the thickness, and serial scans track recovery and warn of relapse.
What does the choroidal vascularity index measure?
The choroidal vascularity index is the ratio of vessel area to total choroid area on binarized images, and it is less sensitive to age and refraction than thickness.
Why should serial choroidal thickness scans be taken at the same time of day?
Brown and colleagues showed diurnal change in choroidal thickness, and caffeine, water intake and exercise can alter it, so repeat scans at the same time of day.

Ahmed Ophthalmologist

Writes and reviews the clinical articles on Educate. Every post is checked against peer-reviewed sources before it goes live.

Choroidal Thickness on EDI-OCT: Measurement and Meaning