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Published on: July 22, 2014
In vivo MRI evaluation of early postnatal development in normal and impaired rat eyes
Jeannie M Au1, Swarupa Kancherla2, Malack Hamade1
1Department of Ophthalmology, NYU Grossman School of Medicine, NYU Langone Health, New York University, New York, NY, USA.
Insights
High-field MRI non-invasively tracks rat eye development and impairments. This technology reveals ocular volume changes and retinal alterations, aiding understanding of visual impairments.
Area of Science:
- Neuroscience
- Ophthalmology
- Biomedical Imaging
Background:
- Postnatal ocular development is crucial for visual function.
- Neonatal impairments can significantly impact eye growth and visual outcomes.
- Non-invasive imaging methods are needed to study these processes in vivo.
Purpose of the Study:
- To evaluate postnatal ocular growth patterns in Sprague-Dawley rats using in vivo 7-Tesla magnetic resonance imaging (MRI).
- To assess the effects of neonatal impairments on ocular development and volume.
- To explore the utility of chromium-enhanced MRI for retinal evaluation.
Main Methods:
- In vivo 7-Tesla MRI (T1- and T2-weighted imaging) was used on Sprague-Dawley rats from postnatal day 1 to 60.
- Ocular volumes (anterior and posterior chamber, lens, vitreous humor) were measured.
- Neonatal impairments included intravitreal potassium dichromate injection, hypoxic-ischemic encephalopathy, monocular deprivation, and enucleation.
Main Results:
- Normal ocular structures exhibited logistic volume increases, with anterior and posterior chambers expanding 33-fold and others fivefold.
- Potassium dichromate induced significant T1-weighted signal enhancement in the developing retina (188-289%).
- Neonatal impairments led to varying degrees of reduced ocular volumes in adult rats.
Conclusions:
- In vivo high-field MRI provides a non-invasive method for evaluating normal and impaired postnatal ocular development in rats.
- Chromium-enhanced MRI is effective for examining the developing retina, potentially related to lipid metabolism.
- Reduced ocular volumes in impaired eyes highlight the need to consider both ocular and neurological factors in visual outcome prediction.
Abstract:
This study employed in vivo 7-T magnetic resonance imaging (MRI) to evaluate the postnatal ocular growth patterns under normal development or neonatal impairments in Sprague-Dawley rats. Using T2-weighted imaging on healthy rats from postnatal day (P) 1 (newborn) to P60 (adult), the volumes of the anterior chamber and posterior chamber (ACPC), lens, and vitreous humor increased logistically with ACPC expanding by 33-fold and the others by fivefold. Intravitreal potassium dichromate injection at P1, P7, and P14 led to T1-weighted signal enhancement in the developing retina by 188-289%. Upon unilateral hypoxic-ischemic encephalopathy at P7, monocular deprivation at P15, and monocular enucleation at P1, T2-weighted imaging of the adult rats showed decreased ocular volumes to different extents. In summary, in vivo high-field MRI allows for non-invasive evaluation of early postnatal development in the normal and impaired rat eyes. Chromium-enhanced MRI appeared effective in examining the developing retina before natural eyelid opening at P14 with relevance to lipid metabolism. The reduced ocular volumes upon neonatal visual impairments provided evidence to the emerging problems of why some impaired visual outcomes cannot be solely predicted by neurological assessments and suggested the need to look into both the eye and the brain under such conditions.
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