1H Spin–Spin Relaxation in Normal and Cataractous Human, Normal Fish and Bird Eye Lenses

Rácz, Péter; Hargitai, C.; Alföldy, Bálint; Bánki, P.; Tompa, K.

doi:10.1006/exer.1999.0812

Cited by 17 publications

(21 citation statements)

References 14 publications

(13 reference statements)

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“…Thus, this very short component cannot be seen in an imaging experiment with a minimum TE of approximately15 msec. For a normal lens, and performing only a single exponential fit, Racz et al (24) report a value of T 2 ϭ 26.98 Ϯ 0.04 msec, which is in excellent agreement with the values found here for both the enucleated (25.0 Ϯ 0.2 msec) and in vivo (25.0 Ϯ 0.4 msec) eye measurements. A detailed physiological explanation of the multiple compartments in the lens is given by Moffat and Pope (25) but is beyond the scope of this work.…”

Section: Discussionsupporting

confidence: 88%

T₁ and T₂ measurements of the fine structures of the in vivo and enucleated human eye

Patz¹,

Bert²,

Frederick³

et al. 2007

Magnetic Resonance Imaging

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Purpose: To measure T 1 and T 2 of the fine structures of the in vivo eye. Materials and Methods:Involuntary saccades make it difficult to obtain artifact-free images. Using a method recently reported (Bert et al, Acad Radiol 2006;12:368 -378), near artifact-free spin-echo images were obtained. Both an isolated enucleated eye and eight human subjects were studied at 1.5T. Spin-echo variable TR/TE data was acquired for T 1 /T 2 determination. Average relaxation times were calculated two ways. First, an arithmetic average over different subjects was computed. Second, all data was normalized using the fitted amplitudes of each data set and pooled to obtain a single least squares fit. BECAUSE OF THE very small size of many structures in the human eye, as well as the difficulty with involuntary patient motion of the eye, high resolution and high signal-to-noise ratio (SNR) MRI of the human eye is technically difficult. There are, however, many reports of ocular MRI in the early literature (1-13). For example, in 1987, Atlas et al (13) retrospectively reviewed their initial experience in 59 patients with MRI of the orbit concluding that there were five specific areas in which MRI ocular imaging provided important information. Imaging at a high field, which was 1.5T in 1987, together with a surface coil and short TR values (600 -800 msec) were very important in increasing SNR so that the acquisition time (using 128 phase encodes) could be kept less than two minutes. For longer values of TR, considerable motion artifacts were observed from both head and eye motion. A number of limitations were noted, including poor specificity. In 1991, Wilms et al (14) reported the results of ocular MRI in 41 patients. Their conclusions were that MRI was superior to computed tomography (CT) in depicting ocular lesions because of multi-planar imaging and higher contrast resolution. Critical determinations of T 1 and T 2 values for ocular structures were not reported.From a technical standpoint, other than implementing surface coils and going to high field, it is useful to employ fast spin-echo (FSE) techniques that reduce total acquisition time by measuring multiple lines of k-space for each acquisition (15). In 2003, Simon et al (16) reported on the use of a three-dimensional T2-weighted FSE method to obtain a spatial resolution of 0.703 mm (readout), 0.938 mm (phase encode), and 1.2-1.6 mm (slice), over an 18 cm field of view (FOV) that included the eye. Total imaging time, however, was fairly long at nine minutes 52 seconds. Clinical results with this method were reported by McCaffery et al (17) and showed that with the thinner slice sections ob-

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Section: Discussionsupporting

confidence: 88%

T₁ and T₂ measurements of the fine structures of the in vivo and enucleated human eye

Patz¹,

Bert²,

Frederick³

et al. 2007

Magnetic Resonance Imaging

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“…However, the most likely explanation for the differences between our data and those of earlier measurements is that in our case we look at segments of the lens while Stankiewicz (1989) and Racz et al (2000) measured the relaxation of whole lenses. Thus our seven lens segments, from anterior cortex to nucleus to posterior cortex, each represented a more homogeneous sample than the whole lens of previous studies.…”

Section: Discussioncontrasting

confidence: 70%

“…Depending on the ®tting of the relaxation curves, NMR measurements may perceive one or up to three different forms of water. Stankiewicz et al (1989) and Racz et al (2000) ®tted their T 2 relaxation of different lenses with a two-term exponential equation and therefore, they calculated relaxation times as well as concentrations of two component systems in the lens. Stankiewicz et al (1989) ®tted the T 1 relaxation of their animal lenses with one-term exponential expression but used the proportions of a two component system gained from analysis of the T 2 relaxation.…”

Section: Discussionmentioning

confidence: 99%

“…In aging and cataractous lenses irreversible syneresis contributes to the turbidity of the lens by increasing the amplitude of refractive index¯uctu-ations (Debye and Bueche, 1949;Bettelheim and Paunovic, 1979). Besides light scattering and thermal studies the role of syneresis in cataractogenesis has been proven by NMR (Racz et al, 1979a(Racz et al, ,b, 1983(Racz et al, , 2000.…”

Section: Introductionmentioning

confidence: 97%

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Relaxographic Studies of Aging Normal Human Lenses

Bettelheim

Lizak

Zigler

2002

Experimental Eye Research

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“…One possible explanation for this paradox maybe due to the fact that in a tissue with such short T1 and T2 constants, the MRI is much more sensitive to the free water content and not the water bound to proteins. 60 Hence, the increase in water content induced by inhibiting the circulation system with ouabain could be explained by an abrupt and localized release of water that is normally bound to proteins in the lens core. This idea is supported by the observation that the ratio of free to bound water gradually increases in human lenses with advancing age and this change is more pronounced in cataractic lenses.…”

Section: Discussionmentioning

confidence: 99%

Active Maintenance of the Gradient of Refractive Index Is Required to Sustain the Optical Properties of the Lens

Vaghefi

Kim

Donaldson

2015

Invest. Ophthalmol. Vis. Sci.

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Citation: Vaghefi E, Kim A, Donaldson PJ. Active maintenance of the gradient of refractive index is required to sustain the optical properties of the lens. Invest Ophthalmol Vis Sci. 2015;56:7195-7208. DOI:10.1167/ iovs.15-17861 PURPOSE. To determine whether the cellular physiology of the lens actively maintains the optical properties of the lens and whether inhibition of lens transport affects overall visual quality. METHODS.One lens from a pair of bovine lenses was cultured in artificial aqueous humor (AAH), while the other was cultured in either AAH-High-K þ or AAH þ 0.1 mM ouabain for 4 hours. Lens pairs or whole enucleated eyes were then imaged in 4.7 Tesla (T) high-field small animal magnet. Lens surface curvatures, T1 measurements of water content, and T2 measurements of water/protein ratios were extracted from cultured lenses, while the geometrical parameters that define the optical pathway were obtained from whole eyes. Gradients of refractive index (GRIN), calculated from T2 measurements, and the extracted geometric parameters were inputted into optical models of the isolated lens and the whole bovine eye. RESULTS.Inhibiting circulating fluxes by inhibiting the Na/K-ATPase with ouabain or depolarization of the lens potential by High K þ caused changes to lens water content, the water/protein ratio (GRIN) and surface geometry that manifested as an increase in optical power and a decrease in negative spherical aberration in cultured lenses. Changes to optical properties of the lens resulted in a myopic shift that impaired vision quality in the optical model of the bovine eye.CONCLUSIONS. The cellular physiology of the lens actively maintains its optical properties and inhibiting the Na/K/ATPase induces a myopic shift in vision similar to that observed clinically in patients who go on to develop cataract.Keywords: lens physiology, magnetic resonance imaging, gradient of refractive index, physiological optics, optical modeling, cataract O ur sense of sight is critically dependent on the optical properties of the ocular lens that enables light to be focused onto the retina.1 Like a glass window, the lens allows light rays that enter the eye to pass through it with minimal scattering. However, the lens is more than a simple pane of glass, because its curved surfaces enable it to focus light. In addition, the lens needs to correct for positive spherical aberration introduced to the optical pathway via the cornea. This spherical aberration is an optical error caused by the increased refraction of light rays that strike the periphery of the cornea relative to those that strike its center.2 The lens compensates for this optical error by imposing and maintaining a compensating negative spherical aberration through the establishment an inherent gradient of refractive index (GRIN). 3Being a biological tissue, this gradient is generated by over expressing different subtypes of crystallin proteins with varying refractive indices, 4 thereby ensuring that incoming light is accurately focussed on the retina. While ...

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1H Spin–Spin Relaxation in Normal and Cataractous Human, Normal Fish and Bird Eye Lenses

Cited by 17 publications

References 14 publications

T₁ and T₂ measurements of the fine structures of the in vivo and enucleated human eye

T₁ and T₂ measurements of the fine structures of the in vivo and enucleated human eye

Relaxographic Studies of Aging Normal Human Lenses

Active Maintenance of the Gradient of Refractive Index Is Required to Sustain the Optical Properties of the Lens

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1H Spin–Spin Relaxation in Normal and Cataractous Human, Normal Fish and Bird Eye Lenses

Cited by 17 publications

References 14 publications

T1 and T2 measurements of the fine structures of the in vivo and enucleated human eye

T1 and T2 measurements of the fine structures of the in vivo and enucleated human eye

Relaxographic Studies of Aging Normal Human Lenses

Active Maintenance of the Gradient of Refractive Index Is Required to Sustain the Optical Properties of the Lens

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Product

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T₁ and T₂ measurements of the fine structures of the in vivo and enucleated human eye

T₁ and T₂ measurements of the fine structures of the in vivo and enucleated human eye