Variability of choroidal and retinal thicknesses in healthy eyes using swept-source optical coherence tomography – implications for designing clinical trials

Figures & data

Figure 1 ETDRS grid used in this study.

Notes: The diameters of the central, middle, and outer rings are 1, 3, and 6 mm, respectively. CRT shows the central region within the 1 mm ring, centered at the fovea.
Abbreviation: ETDRS, Early Treatment Diabetic Retinopathy Study.

Table 1 Summary of demographic characteristics

Variables	Values
Age (years)	33.40±16.36 (range: 11–79)
Sex, n (%)
Male	45 (36.6%)
Female	78 (63.4%)
	Right eye	Left eye
Spherical refraction (D)	−0.86±1.86 (range: −6.50 to +2.0)	−0.84±1.95 (range: −6.25 to +2.50)
Cup-to-disk ratio	0.25±0.10 (range: 0–0.5)	0.26±0.10 (range: 0.1–0.5)
Axial length (mm)	24.01±1.26 (range: 21.19–28.63)	23.97±1.28 (range: 21.11–28.44)

Note: Values shown as n (%) or mean ± standard deviation (range).

Table 2 Partial correlation between retinal and choroidal thicknesses, age, and axial length

Variables	Age		Axial length
	ra	p-valuea	rb	p-valueb
Mean thickness (RETINA)	−0.208	0.023	−0.220	0.016
Mean thickness in CRT (RETINA)	−0.012	0.894	0.230	0.012
Mean thickness (RNFL)	−0.085	0.356	0.367	<0.0001
Mean thickness in CRT (RNFL)	−0.096	0.299	0.395	<0.0001
Mean thickness (GCLIPL)	−0.209	0.022	−0.257	0.005
Mean thickness in CRT (GCLIPL)	−0.040	0.665	0.260	0.004
Mean thickness (RNFLGCLIPL)	−0.180	0.050	−0.021	0.820
Mean thickness in CRT(RNFLGCLIPL)	−0.058	0.533	0.316	0.0004
Mean thickness (CSI)	−0.426	<0.0001	−0.504	<0.0001
Mean thickness in CRT (CSI)	−0.368	<0.0001	−0.513	<0.0001

Notes: For this purpose, measurements from the right eye and the left eye for each individual were averaged.

a Adjusted for sex and axial length.

b Adjusted for sex and age.

Abbreviations: CRT, central retinal thickness; CSI, choroid scleral interface; RETINA, total retinal thickness from internal limiting membrane to Bruch’s membrane; RNFL, retinal nerve fiber layer; GCLIPL, Ganglion cell layer and inner plexiform layer; RNFLGCLIPL, sum of retinal nerve fiber layer to inner plexiform layer.

Figure 2 (A) Bland–Altman plot between CSI thickness of the right and left eyes within the 6 mm grid in the ETDRS grid. (B) Bland–Altman plot of CSI thickness between the right and left eyes within the CRT grid.

Abbreviations: CRT, central retinal thickness; CSI, choroidal sclera interface; ETDRS, Early Treatment Diabetic Retinopathy Study; SD, standard deviation.

Table 3 Sample size calculations

Type of study	Total patients required using standard deviations of:
	50	100	200	300	400
Uniocular surgery or treatment using fellow eye as control (one group)a	5	11	36	78	136
Two groups of uniocular surgery or treatmentb	12	36	136	304	540

Notes: α=0.05, power =0.9 for all calculations. Difference to detect choroidal sclera interface thickness is set at 112 µm, either to the fellow eye or to other treatment/surgery groups. Assuming no loss to follow-up.

a Student’s t-test for comparing difference between two dependent mean values (matched pairs).

b Student’s t-test for comparing difference between two independent mean values (two groups).