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Editors Selection IGR 7-2

Basic Research: MRI for ocular anatomic changes

Comment by James Lindsey on:

22178 Manganese-enhanced MRI of the DBA/2J mouse model of hereditary glaucoma, Calkins DJ; Horner PJ; Roberts R et al., Investigative Ophthalmology and Visual Science, 2008; 49: 5083-5088

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The contrast of magnetic resonance images of the retina can be enhanced by systemic administration of manganese chloride. Calkins et al. (1389) used this approach to compare age-related changes in ocular anatomical measurements and image intensity measurements within normal C57BL/6 mice and DBA/2J mice that spontaneously develop elevated intraocular pressure. Between 3 and 10-11 months of age, they observed that the iridocorneal angle increased in the normal mice, but markedly decreased in the DBA/2J mice. Optic nerve head width was unchanged in the normal mice and dramatically increased in DBA/2J mice. In contrast, the ciliary body area was unchanged in the normal mice, but markely decreased in the DBA/2J mice. Smaller differences were noted in a number of structures. Also, manganese uptake distribution within the aged Basic Research DBA/2J retina differed from the pattern observed in young and aged normal mice and young DBA/2J mice. In general the study appears to have been done carefully. The authors pointed out that some of the retinal differences they observed were less than the pixel size within the original images. The resolution of this method was less than has been recently achieved with optical coherence tomography. The authors claim, however, that because differences in the image signal are likely related to differences in calcium uptake, the physiological value of the images is greater. Although this may possible in the future, the present limited understanding of the basis for image intensity differences means that conclusions relying on this point remain speculative.

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