Axial length may affect macular disease evaluation

By Sarah Guy

Korean researchers report that thinner macular retinal thickness, lower macular volume, and greater foveal thickness are associated with longer axial length in young individuals with myopic eyes.

The finding indicates that axial length might affect the accuracy of evaluation for various macular diseases, they say. For example, thin maculae in eyes with long axial length may cause false-positive diagnoses for macular disease with retinal thinning.

"These associations should be considered when interpreting Cirrus HD-OCT [spectral-domain optical coherence tomography] macular measurements," suggest Young Hoon Hwang (Konyang University, Seoul, Korea) and Yong Yeon Kim (University College of Medicine, Seoul).

The pair investigated associations between refractive error/axial length and macular thickness in a group of 336 healthy males aged an average 21 years with visual acuity 6/6 or better, normal intraocular pressure, and no retinal abnormalities aside from myopic peripapillary atrophy, to determine whether age affected myopic changes in the macular.

Participants underwent full optical examination, and scans using the Cirrus HD-OCT to determine macular thickness (and inner and outer macular thickness), foveal thickness, and macular volume. The researchers grouped participants into tertile levels of spherical equivalent (SE) and axial length: S1 - less than 3.50 diopter (D), n=103; S2 - at least 3.50 D and less than -1.25 D, n=118; and S3 - at least -1.25 D, n=115. Of note, age did not differ significantly between groups.

Hwang and Kim report that groups with greater myopia had significantly thinner average macula, thinner inner and outer macula, thicker fovea, and lower macular volume, at respective values of 276.0, 316.2, 271.5, 262.5 µm, and 9.9 mm³ in group S1, versus 285.1, 324.2, 283.6, 255.2 µm, and 10.3 mm³ for those in group S3.

Similarly, write the researchers in Clinical and Experimental Optometry, when they compared macular thicknesses/volumes of the three groups divided by axial length, those with greater length had thinner average macula, thinner inner and outer macula, thicker fovea, and lower macular volume.

Indeed, greater foveal thickness in eyes with long axial length could induce false-positive diagnoses for macular disease with foveal thickening, say the authors.

"Given that axial length-induced magnification can affect OCT scan radius, the effect of magnification on OCT macular measurements should be considered in myopic eyes," they conclude.

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