Table 2. Comparison of Rates of Change in Retinal Thickness Among Patients With Sickle Cell Retinopathy With Different Hemoglobin Types, as Measured by Spectral-Domain Optical Coherence Tomography.

ETDRS subfield	Sickle cell hemoglobin subtype						Results of statistical tests comparing rates among the 3 hemoglobin subtypes
	HbSS (219 eyes)		HbSC (92 eyes)		HbS-β-thalassemia (33 eyes)
	Difference (95% CI)	P value	Difference (95% CI)	P value	Difference (95% CI)	P value	χ2	df	P value
Central	−0.31 (−0.96 to 0.34)	.35	−0.52 (−1.25 to 0.22)	.17	−1.21 (−2.45 to 0.03)	.05	8.78	2	.01
Inner
Nasal	−1.03 (−1.64 to −0.43)	.001	−1.25 (−1.91 to −0.59)	<.001	−1.90 (−3.10 to −0.70)	.002	7.25	2	.03
Superior	−0.81 (−1.62 to 0.00)	.05	−1.39 (−2.42 to −0.36)	.01	−1.56 (−3.25 to 0.14)	.07	5.24	2	.07
Temporal	−0.39 (−0.93 to 0.15)	.16	−0.80 (−1.42 to −0.18)	.01	−1.36 (−2.32 to −0.39)	.006	7.55	2	.02
Inferior	−0.34 (−0.84 to 0.16)	.18	−0.33 (−0.82 to 0.15)	.18	−0.87 (−1.65 to −0.09)	.03	2.59	2	.27
Outer
Nasal	−0.37 (−0.72 to −0.03)	.03	−0.40 (−0.90 to 0.10)	.11	−0.79 (−1.45 to −0.13)	.02	2.28	2	.32
Superior	−0.19 (−1.09 to 0.71)	.68	−0.45 (−1.87 to 0.97)	.53	−1.23 (−2.27 to −0.21)	.02	1.78	2	.41
Temporal	−0.43 (−1.45 to 0.59)	.41	−0.45 (−1.18 to 0.28)	.22	−1.01 (−2.19 to 0.16)	.09	0.81	2	.67
Inferior	−0.08 (−0.57 to 0.42)	.76	−0.05 (−0.81 to 0.72)	.91	−0.40 (−1.31 to 0.52)	.40	0.72	2	.70

Abbreviations: ETDRS, Early-Treatment Diabetic Retinopathy Study; HbS-β-thalassemia, hemoglobin β-thalassemia: HbSC, hemoglobin C; HbSS, hemoglobin SS.