PubMed · 13707978
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E GRAUE, C ZALDIVAR. [Ocular prothesis].. https://pubmed.ncbi.nlm.nih.gov/13707978/
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RATIONALE AND OBJECTIVES: We studied preparatory strategies for high-resolution human eye in vivo imaging with commercially available magnets and coils. MATERIALS AND METHODS: We imaged normal volunteers on 1.5T systems by Philips, GE, and Siemens, using commercial approximately 9 cm temporomandibular joint receive coils. Subjects fixated the nonimaged eye on a target. We compared signal (S) to tissue noise (Nt) and system noise (Ns) between images acquired with the imaged eye: 1) open, 2) held closed, 3) taped closed, and 4) taped closed with overlying water-soaked gauze. We standardized technique 4 to compare studies between manufacturers using T1-weighted parameters (repetition time/echo time/flip angle/number of signal averages = 400 ms/10-17 ms/90 degrees /4-6, in-plane resolution approximately 250 x 250 microm2; 2-3 mm slices, image time = 4.3-5.2 min). We obtained similar images of an enucleated human eye to estimate in vivo effects of microsaccades and ocular pulsations. RESULTS: Measurements of S/Nt and S/Ns gave surprising results of Nt < Ns in some instances. Ns/Nt was congruent with 1, varying approximately 20%, when the eye was taped shut and covered with water-soaked gauze. T1-weighted spin echo sequences, using technique 4, produced high-quality images with good S/Nt on all systems. Images from the three manufacturers were comparable when parameters were normalized for pulse repetition time, echo time, number of signal averages, bandwidth in Hz/pixel, and reconstruction matrix. Images of the enucleated eye produced S/Nt ratios that were comparable to in vivo images in some structures. CONCLUSIONS: Our best preparatory technique produced images with in-plane resolution of approximately 250 mum in 4-5 minutes with three commercial 1.5 T systems. The in vivo S/Nt was comparable to in vitro values in most solid tissues but decreased in most fluid compartments.
Microbial agents have an important role in the pathogenesis of various inflammatory eye diseases, such as uveitis and keratitis. Microbial infections of the eye such as microbial keratitis, ocular onchocerciasis, bacterial endophthalmitis, viral retinitis, and other infectious uveitis are unfortunately common. In addition, microbial agents have been implicated in the pathogenesis of "non-infectious" immune mediated diseases such as HLA-B27 associated acute anterior uveitis. Toll-like receptors (TLR) are a family of pattern recognition receptors that initiates rapid host innate immune response to microbial components known as pathogen associated molecular patterns, which are unique to a given class of microbes, such as lipopolysaccharide of Gram negative bacteria. Recent in vitro and in vivo studies have demonstrated the expression and function of TLRs in the eye, with significant implications for better understanding of ocular immunity and the pathogenesis of inflammatory eye diseases affecting the cornea, uvea, and retina.
Brain neuronal dysfunction has been implicated in pathogenesis of migraine but direct evidence is lacking. Scintillating scotoma of migraine is generally believed to originate at the visual cortex. While cortical spreading depression is a relatively late physiological alteration in migraine, its protective role in neuronal ischaemia is increasingly being recognized. Atenolol, nadolol, or verapamil prevent migraine but do not readily cross the blood-brain barrier or critically influence any brain or peripheral neuronal function. Typical migraine headache, aura, or scintillating scotoma has not been reported following enucleation or evisceration of the eye. In humans, pain and temperature fibres from only the ophthalmic division of the trigeminal nerve reach the upper cervical spinal segments. Pain in migraine attacks including occipital and nuchal discomfort reflects selective involvement of the ophthalmic nerve. Photophobia is largely a retinal reflex involving the ophthalmic division of the trigeminal nerve. Key clinical features of the migrainous scintillating scotoma are consistent with retinal origin. Spreading depression in the retina is well-established. A subtle regional ocular sympathetic deficit prevails in migraine patients and possibly impairs regulation of intraocular choroidal blood volume and intraocular pressure. Several first-line migraine prophylactic agents lower the intraocular pressure. The neuro-ophthalmological basis for a monocular origin of migrainous scintillating scotomata due to mechanical deformation of the posterior segment of the corneo-scleral envelope consequent to choroidal venous congestion and rise in intraocular pressure is presented. Study of distribution and displaceability of the migrainous scintillating scotoma can settle its site of origin. Headache of migraine possibly arises from a similar mechanical deformation of the anterior eye segment followed by antidromic discharge in the trigeminovascular system. Lateralizing negative deficits such as homonymous hemianopia probably reflect vasospastic complications of migraine. A rational explanation for the most characteristic clinical features of migraine and a new template to elucidate the pharmacological basis of anti-migraine drugs is offered.