Caution advised over OCT measurement of thick choroid

By Lucy Piper, Senior medwireNews Reporter

Enhanced depth imaging optical coherence tomography (EDI-OCT) is consistent for measuring choroidal thickness, researchers confirm, but its accuracy may be impaired in eyes with a very thick choroid.

Precise measurement of choroidal thickness is crucial in understanding the pathophysiology of various ocular diseases, but indistinct choroidal junctions can make it difficult to measure, notes the team.

To determine the reliability of manual choroidal thickness measurement and investigate the influence of image scale setting, researchers Yun Kim (Ewha Womans University, Seoul, South Korea) and colleagues assigned two ophthalmologists to measure the subfoveal choroidal thickness of 189 eyes in 189 adults from 1:1 micron and 1:1 pixel images obtained from EDI-OCT scanning.

The participants, aged an average of 45 years, were categorised into three groups according to predefined choroidal thickness definitions of: thin (≤211 µm), intermediate (>211 to ≤363 µm) and thick (>363 µm).

Based on a total mean choroidal thickness measurement from the two ophthalmologists for the 1:1 pixel image, 26 eyes were classified as thin, 111 as intermediate and 52 as thick . The average subfoveal choroidal thickness for the three subgroups were 180.0 µm, 295.4 µm and 425.3 µm, respectively.

For the 1:1 micron image, the average subfoveal choroidal thicknesses were 180.0 µm for the thin group, 292.2 µm for the intermediate group and 421.6 µm for the thick group.

Agreement between the two ophthalmologists on choroidal thickness measurement was high, as was intraobserver repeatability, regardless of image setting. But the researchers note in Eye that interobserver agreement was reduced for patients with thick measurements, particularly on 1:1 pixel images.

In the thick group, 25.0% of eyes displayed a significant interobserver gap and nine eyes had vague chorio-scleral interface (CSI), the researchers report. By contrast, a significant interobserver gap was evident in just 3.8% of eyes in the thin group and 11.7% of eyes in the intermediate group, of which only four in the intermediate group had vague CSI.

“This result suggests that indistinct CSI, which was frequent in eyes with thick [choroidal thickness], may be an important impeding factor in the measurement of [choroidal thickness ]”, say Kim et al.

They conclude: “Intraobserver [choroidal thickness] measurements could be useful for investigation of disease characteristics and progression.

“However, attention should be paid during interpretation of numerical [choroidal thickness] values reported by different observers or at different facilities, especially in thick choroids.”

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