Choroidal Thickness in Normal EyesMeasured using Cirrus HD

Optical Coherence Tomography

journal critique

By: Manal Al-RomeihOpto 541

Hypothesis

to evaluate the Cirrus HD-OCT device to see if its new software would allow accurate measurement of choroidal thickness and area in normal eyes.

to determine the correlation between retinal thickness and choroidal thickness.

Methods

Thirty four eyes of 34 subjects were measured (one eye per subject).

With no retinal or choroidal disease.

Methods

Subjects with myopia greater than -6.0 D were excluded.

Spectral-domain optical coherence tomography (SD-OCT) with frame enhancement software was used.

Emit lights into the eye; measure reflectivity of the tissues within a target cubeRendering the measurements for visualizing inner-structures

Methods

Statistical analysis (Pearson correlation) was used to correlate inter-observer findings, choroidal thickness and area measurements with age, and choroidal thickness with retinal foveal thickness.

2 independent observers measured:

1- choroidal thickness perpendicularly from the posterior edge of RPE to the choroid/sclera junction at 500 µm intervals up to 2500 µm temporal and nasal from the fovea.

2- central foveal thickness.

3- Central 1-mm area of the choroid, 500 µm temporal and nasal to the fovea.

Histological picture showing the choroid boundaries

(Top) Demonstration of normal choroidal thickness measured at 500µm intervals, up to 2500µm temporal and nasal to the fovea. Perpendicular lines were drawn from the

posterior edge of the RPE to the choroid/sclera junction using Cirrus HD-OCT software.

(Bottom) Central 1-mm cross-sectional area of choroid measured using Image analysis software; outlined area is 0.32 mm2

.

Results

choroidal thickness measurements had strong inter-observer correlation overall (r = 0.92, P ˂.0001).

Average thickness of the choroid beneath the fovea was 272 µm (SD, ±81 µm).

Results Mean choroidal thickness at each location was

plotted ,and the choroid was noted to be thinnest nasally, thicker in the subfoveal region, and then thinner again temporally but not as thin as the choroid proximal to the disc.

There was weak correlation between central foveal thickness of the retina and choroidal thickness in the area directly beneath the fovea (r=-.23, P =.18)retinal thickness aren’t directly related to choroidal thickness in normal eyes.

Graph of mean macular choroidal thickness in normal eyes. Mean thickness at each of the 11 locations measured at 500 µm (0.5˜mm)

intervals temporal (T) and nasal (N) to the fovea (F).

This article raised a good topic since:

The choroid plays a vital role in the patho-physiology of many diseases affecting the retina.

Measuring it in vivo was necessary to accurately determine its true structure and thickness due to its high vascularization.

Using OCT imaging techniques is a noninvasive way to determine optical biopsy of the posterior segment.

Continuation & confirmation of previous studies that already:

revealed choroidal thickness relative to diseases such as: • central serous chorioretinopathy • myopic degeneration

defined new entities such as:• age-related choroidal atrophy

Obtained an average of the choroidal thickness in normal eyes that will be helpful diagnostically (to track changes).

Obstacle faced measurement of choroidal thickness

1- Information regarding choroidal thickness in normal eyes was based primarily on histologic results, which do not necessarily reflect the true measurements of it, since histologic fixation produces artifacts because of processing, tissue deformation, and shrinkage.

2- adequate visualization of the choroid using OCT hasn’t been possible until recently when Spaide and associates used spectral domain OCT instrument which offers eye tracking technology and the capability to capture up to 100 B-scans.

Manjunath et alSpaide et al

34 (34 eyes)30 (54 eyes)Subjects (eyes)

51.1 yrs50.4 yrsMean age

r = −0.62-ve (↓15.6 μm/decade)Age/choroidal

thickness correlation

272 μm 287 μmChoroidal thickness

(subfoveal)

New software (raster scan)positioning a SD-OCT device close

enough to the eye to acquire an

inverted image

Technique

Apr 2010Dec 2008Date

Weak points of this study

1- inability to measure choroidal thickness in all eyes because of an unclear posterior boundary of the choroid (choroid/ sclera junction) in approximately one quarter of eyes.

2- insufficient number of subjects.

3- The previous study done by Spaide & Margolis confirmed the integrity of the new software used in this study.

One study isn’t enough for good judgment.

Conclusion

• This study led a good research regarding choroidal thickness in normal eyes since there is lack in studies in this field.

• On the other hand, evaluating the new cirrus soft ware had no strong credibility due to insufficient references in normal choroidal thickness.

.Thanks for listening