Susan A. Strenk

Magnetic resonance imaging of aging, accommodating, phakic, and pseudophakic ciliary muscle diameters

PURPOSE: To quantify in vivo accommodative changes in the aging human ciliary muscle diameter in phakic and pseudophakic eyes. SETTING: Department of Surgery/Bioengineering, UMDNJ–Robert Wood Johnson Medical School, Piscataway, and the Institute of Ophthalmology and Visual Science UMDNJ–New Jersey Medical School, Newark, New Jersey, USA. METHODS: Images were acquired from 48 eyes of 40 people between the ages of 22 and 91 years, 1 eye of 32 phakic volunteers and both eyes of 8 patients who had monocular implantation of a single‐piece AcrySof intraocular lens (IOL) (Alcon Laboratories). Images were acquired during physiological accommodation and with accommodation at rest, and the diameter of the ciliary muscle ring was measured. RESULTS: Results show the ciliary muscle remains active throughout life. The accommodative change in its diameter (mean 0.64 mm) (P<.00001) was undiminished by age or IOL implantation. Preliminary data showed that the accommodative decrease in muscle diameter in phakic and pseudophakic eyes was statistically identical. The phakic eyes had a marked decrease in ciliary muscle diameter with advancing age for both accommodative states (P<.000001 and P<.000001), which did not appear to be altered by IOL implantation. The lens equator was constant with age in the unaccommodated human eye, resulting in decreased circumlental space with advancing age in the phakic eyes. CONCLUSION: Although the undiminished ability of the ciliary muscle to decrease its diameter with accommodation can be relied on in strategies for presbyopia correction, even in advanced presbyopia, the decreasing circumlental space and its potential effects on zonular tension must also be considered.

Scheimpflug and high-resolution magnetic resonance imaging of the anterior segment: a comparative study.

High-resolution imaging with a camera system built on the Scheimpflug principle has been used to characterize the geometry of the anterior segment of the adult human eye as a function of aging and accommodative state but is critically dependent on algorithms for correction of distortion. High-resolution magnetic resonance imaging (MRI), in contrast, provides lower-resolution information about the adult eye but is undistorted. To test the accuracy of the Scheimpflug correction methods used by Cook and Koretz [J. Opt. Soc. Am. A 15, 1473 (1998)]; [Appl. Opt. 30, 2088 (1991)], data on anterior chamber and segment lengths, as well as lens thickness and anterior and posterior curvatures, were compared with corresponding MRI data for adults aged 18-50 at 0 diopter accommodation. Excellent statistical agreement was found between the MRI and the Scheimpflug data sets with the exception of the posterior lens radius of curvature, which is less well defined than the other measurements in the Scheimpflug images. The considerable agreement between data obtained with MR and Scheimpflug imaging, two different yet complementary in vivo imaging techniques, validates the Scheimpflug correction algorithms of Cook and Koretz and suggests the capability of directly integrating information from both. A third, equivalent, data set obtained with a Scheimpflug-style camera system differs considerably from both Scheimpflug and MRI results in magnitude and age dependence, with negative implications for this alternative method and its correction procedures.

Magnetic resonance imaging of the anteroposterior position and thickness of the aging, accommodating, phakic, and pseudophakic ciliary muscle

PURPOSE: To quantify accommodative and age‐related changes in the anteroposterior position and thickness of the ciliary muscle in phakic and pseudophakic eyes. SETTING: Department of Surgery/Bioengineering, UMDNJ–Robert Wood Johnson Medical School, Piscataway; Institute of Ophthalmology and Visual Science UMDNJ–New Jersey Medical School, Newark, New Jersey; MRI Research, Inc., Middleburg Heights, Ohio, USA. METHODS: Magnetic resonance images were taken of phakic and pseudophakic eyes. RESULTS: The cohort comprised 32 phakic volunteers and 8 volunteers with a monocular intraocular lens (IOL) aged 22 to 91 years. No anteroposterior accommodative movement of the ciliary muscle apex occurred in either group. The muscle moved closer to the cornea with advancing age in phakic eyes; IOL implantation returned the muscle to a youthful position. An age‐dependent increase in ciliary muscle anteroposterior thickness occurred that was not mitigated by IOL implantation. Muscle thickness increased with accommodation in only phakic eyes. CONCLUSIONS: Presbyopia‐correction strategies cannot rely on accommodative anterior movement of the ciliary muscle. Forces on the uvea by crystalline lens–pupillary margin contact may increase with accommodation and lens growth, producing accommodative and age‐dependent increases in muscle thickness and significant age‐dependent anterior muscle displacement. Intraocular lens implantation removed these forces, allowing choroidal elasticity to restore the muscle to a youthful position; however, the increase in thickness was permanent and likely due to an age‐dependent increase in connective tissue. This supports the geometric theory of presbyopia development and that the mechanical forces in human accommodation and presbyopia are very different from those in the rhesus monkey model. Financial Disclosure: S. A. Strenk and L. M. Strenk have a proprietary interest in the purpose‐built eye coil. Dr. Guo has no financial or proprietary interest in any material or method mentioned.

Surface coil for high resolution imaging using a magnetic resonance imaging apparatus

The present invention provides an RF receiver coil with improved signal-to-noise ratio (SNR) characteristics, designed to be positionable immediately adjacent to or surrounding the anatomical region of the body of the patient which is desired to be imaged. The surface coil of the invention is designed for use as a signal receiver, for high resolution unilateral imaging of a localized region, with improved penetration depth. The RF surface coil minimizes capacitive coupling to the patients body, and in conjunction therewith reduces resistive coupling of the coil to the body of the patient. The RF receiver coil of the invention includes at least two turns of an electrical conductor formed in a solenoidal configuration, with the at least two turns being positioned in spaced apart relationship defining an interturn spacing therebetween. Each of the turns of the coil includes a predetermined number of capacitive splits spaced at intervals along the length of the conductor forming the turns. The predetermined number of capacitive splits reduces capacitive coupling of the coil to the body of the patient, and thus, limits the effect of the body on the coil performance.

Pathologic Assessment of Complications with Asymmetric or Sulcus Fixation of Square-Edged Hydrophobic Acrylic Intraocular Lenses

OBJECTIVE One-piece hydrophobic acrylic intraocular lenses (IOLs) are not indicated for sulcus fixation because of complications, such as uveitis-glaucoma-hyphema syndrome. Similar complications may also be observed with 3-piece lenses that have a square optic edge on the anterior surface. The objective of this study was to provide pathologic evidence of complications related to out-of-the-bag fixation of 1- or 3-piece hydrophobic acrylic IOLs with anterior and posterior square optic edges. DESIGN Comparative case series with pathology. PARTICIPANTS A total of 661 pseudophakic cadaver eyes obtained from eye banks within the United States, implanted with different IOLs. METHODS Anterior segment scanning of whole eyes with a high-frequency ultrasound system or high-resolution anterior segment magnetic resonance imaging, followed by gross examination. Selected eyes were processed for complete histopathologic analysis; some of them were explanted before histopathology to allow for direct light microscopic evaluation of the lenses. MAIN OUTCOME MEASURES Findings from imaging, gross, and histopathologic evaluation that could be related to out-of-the-bag fixation of the lenses. RESULTS A total of 256 eyes were implanted with hydrophobic acrylic IOLs with anterior and posterior square optic edges; 18 of them exhibiting asymmetric or sulcus IOL fixation (six 1-piece and twelve 3-piece IOLs) underwent complete histopathologic evaluation and were compared with the contralateral eyes with symmetric in-the-bag IOL implantation. Pathologic findings were composed of IOL decentration and tilt, pigmentary dispersion within the anterior segment and on the IOL surface, iris transillumination defects, iris changes including vacuolization/disruption/loss of the pigmented layer, iris thinning, and iris atrophy, as well as synechiae and loop erosion in the case of 3-piece lenses. Findings were more significant in comparison with the control contralateral eyes and were particularly evident in relation to the sulcus-fixated haptic in the case of 1-piece lenses. The majority of the eyes with 3-piece lenses showed signs of complicated surgery. CONCLUSIONS This study provides pathologic correlation of complications that were clinically reported in the peer-reviewed literature in relation to sulcus fixation of 1-piece hydrophobic acrylic IOLs. The eyes with 3-piece lenses generally exhibited evidence of complicated surgery; therefore, all pathologic findings in those cases may not be strictly attributed to the out-of-the-bag fixation.

Pathologic Comparison of Asymmetric or Sulcus Fixation of 3-Piece Intraocular Lenses with Square Versus Round Anterior Optic Edges

OBJECTIVE To evaluate the pathologic findings of 3-piece intraocular lenses (IOLs) with asymmetric or sulcus fixation in pseudophakic cadaver eyes, comparing IOLs with square or round edges on the anterior optic surface. DESIGN Comparative case series with pathology. PARTICIPANTS A total of 661 pseudophakic cadaver eyes, obtained from eye banks within the United States, implanted with different IOLs. METHODS Anterior segment scanning of whole eyes with a high-frequency ultrasound system or high-resolution anterior segment magnetic resonance imaging followed by gross examination. Selected eyes were processed for complete histopathologic analysis. MAIN OUTCOME MEASURES Findings from imaging, gross, and histopathologic evaluation that could be related to out-of-the-bag fixation of the lenses. RESULTS Of 661 pseudophakic cadaver eyes obtained, 13 had 3-piece hydrophobic acrylic IOLs with anterior and posterior square optic edges, and 14 had 3-piece lenses with anterior round edges (13 silicone lenses and 1 hydrophobic acrylic lens) without symmetric in-the-bag fixation. These 27 selected eyes were processed for complete histopathologic analysis. Gross findings in both groups were composed of IOL decentration and tilt, pigmentary dispersion within the anterior segment and on the IOL surface, and iris transillumination defects. Histopathology of the 14 eyes with 3-piece IOLs with round anterior optic edges showed mild focal disruption of the iris pigmented layer and loop protrusion/erosion in the ciliary sulcus. Additional changes observed in the 13 eyes with square anterior optic edge IOLs included iris changes, such as vacuolization, disruption and loss of the pigmented epithelial layers, iris thinning and atrophy, synechiae, and pigmentary dispersion within the trabecular meshwork. One eye also exhibited initial signs of optic nerve disc cupping. CONCLUSIONS In this series, pathologic findings were more severe in eyes implanted with 3-piece IOLs with square anterior optic edges, suggesting that IOLs with round anterior edges are more suitable for sulcus fixation. FINANCIAL DISCLOSURE(S) Proprietary or commercial disclosure may be found after the references.

Reply to comment on “Scheimpflug and high-resolution magnetic resonance imaging of the anterior segment: a comparative study”

We dispute the claim made by Dubbelman and colleagues [J. Opt. Soc. Am. A22, 1216 (2005); this issue] that “incorrect statistical methods” were used to compare the MRI and Scheimpflug data. We clearly stated that we “analyzed the covariance of regression lines” in the results section. We believe the analysis of covariance of regression lines, as shown by Snedecor and Cochran [Statistical Methods (Iowa State U. Press, Ames, Iowa, 1989)] is as “correct” as the “straightforward statistical comparison” of confidence intervals employed by Dubbelman and colleagues; however; our statistical method has the benefit of being more precise and stringent than a simple comparison of confidence intervals.

High resolution MRI study of circumlental space in the aging eye.

he controversy and confusion regarding the mechanism of presbyopia results in large part from an inability to directly measure the anatomical structures in question. In this study, magnetic resonance imaging (MRI) has been used to directly detect age related changes in circumlental space of 47 emmetropes and mild myopes. MRI offers unparalleled soft tissue contrast, providing differentiation between muscle and other soft tissue, thus allowing the ciliary muscle to be visualized. Moreover, MRI produces undistorted images of the entire lens surface. As previously presented 1 , both the ciliary muscle ring diameter and the circumlental space decrease with age, the decrease in circumlental space is primarily the result of an age dependent decrease in the ciliary muscle ring diameter since the length of the lens equator is not significantly correlated with age. Recently, investigators 2 found evidence that the lens is not symmetrically positioned in the ciliary ring of the rhesus monkey. Specifically, Croft and colleagues 2 reported that during resting accommodation, the temporal ciliary processes are 0.21 mm closer to the lens equator than to the nasal ciliary processes. Here,we present MRI based on data that demonstrate this asymmetry also occurs in the position of the human lens. METHODS A 1.5 Tesla MR imager (1.5T-Signa, General Electric Medical Systems, Waukesha, WI) was used to obtain images from 47 subjects, ages 21 through 83. The soft tissue image contrast available with MRI is superior to that obtained with any other imaging modality. Moreover, by varying MR pulse sequences and timing parameters, desired contrast differences can be maximized. We used a T1 weighted spin-echo pulse sequence to differentiate between muscle and other soft tissue, while clearly delineating lens shape. A series of contiguous axial slices through the lens were acquired simultaneously, requiring 5 minutes. These images were collected with a 4 cm field-of-view and 256 x 256 pixel matrix, resulting in 0.156 mm in-plane resolution. The contiguous 3 mm thick axial slices ensured that the entire lens was captured and allowed the desired “center” slice as well as its flanking slices to be evaluated in order to determine the lens dimensions, as previously described. 3 A custom eye coil consisting of a three-turn solenoid with a 2.5 cm diameter, posi