Biomedical subjects

Thom Terwee

Publications and source records attributed to Thom Terwee.

8 recordsLinked to original sources

PubMed2006

Development of an accommodating intra-ocular lens--in vitro prevention of re-growth of pig and rabbit lens capsule epithelial cells.

Cataract surgery is routinely performed to replace the clouded lens by a rigid polymeric intra-ocular lens unable to accommodate. By implanting a silicone gel into an intact capsular bag the accommodating properties of the natural lens can be maintained or enhanced. The implantation success of accommodating lenses is hampered by the occurrence of capsular opacification (PCO) due to lens epithelial cell (LEC) growth. In order to prevent LEC proliferation, a treatment regime using actinomycin D, cycloheximide and water was developed. The effectiveness of treatment was analyzed using an in vitro, MTT-based cell culture system and an ex vivo pig eye model in which the implanted lens-in-the-bag is cultured as a whole. LEC were exposed to treatment solutions for 5 min, then the cells were allowed to recover and to re-colonize the substratum. MTT conversion by cells was transiently inhibited by cycloheximide dissolved in water and by water alone. Exposure to actinomycin D resulted in a lasting inhibition of MTT conversion and consequently cell proliferation. These in vitro data could not be fully reproduced in the ex vivo pig eye model due to essential differences between both models. Treatment with actinomycin D containing solutions, however, resulted in a nearly complete absence of cells on the capsular wall. The pig eye model is a promising approach to further evaluate the effects of peri-surgical treatment during the accommodating intra-ocular lens implantation.

Animals↗

PubMed2006

Artificial crystalline lens.

If presbyopia is caused by hardening of the crystalline lens, replacing it with a material with mechanical properties similar to the young crystalline lens should restore accommodative ability. Such a silicone material has been developed. Refilling the capsular bag with this material results in 3 to 5 D of accommodation in primates in response to pilocarpine.

Animals↗

PubMed2006

Accommodative lens refilling in rhesus monkeys.

PURPOSE: Accommodation can be restored to presbyopic human eyes by refilling the capsular bag with a soft polymer. This study was conducted to test whether accommodation, measurable as changes in optical refraction, can be restored with a newly developed refilling polymer in a rhesus monkey model. A specific intra- and postoperative treatment protocol was used to minimize postoperative inflammation and to delay capsular opacification. METHODS: Nine adolescent rhesus monkeys underwent refilling of the lens capsular bag with a polymer. In the first four monkeys (group A) the surgical procedure was followed by two weekly subconjunctival injections of corticosteroids. In a second group of five monkeys (group B) a treatment intended to delay the development of capsular opacification was applied during the surgery, and, in the postoperative period, eye drops and two subconjunctival injections of corticosteroids were applied. Accommodation was stimulated with carbachol iontophoresis or pilocarpine and was measured with a Hartinger refractometer at regular times during a follow-up period of 37 weeks in five monkeys. In one monkey, lens thickness changes were measured with A-scan ultrasound. RESULTS: In group A, refraction measurement was possible in one monkey. In the three other animals in group A, postoperative inflammation and capsular opacification prevented refraction measurements. In group B, the maximum accommodative amplitude of the surgically treated eyes was 6.3 D. In three monkeys the accommodative amplitude decreased to almost 0 D after 37 weeks. In the two other monkeys, the accommodative amplitude remained stable at +/-4 D during the follow-up period. In group B, capsular opacification developed in the postoperative period, but refraction measurements could still be performed during the whole follow-up period of 37 weeks. CONCLUSIONS: A certain level of accommodation can be restored after lens refilling in adolescent rhesus monkeys. During the follow-up period refraction measurements were possible in all five monkeys that underwent the treatment designed to prevent inflammation and capsular opacification.

Accommodation, Ocular↗

PubMed2005

Comparison of the accommodation theories of Coleman and of Helmholtz by finite element simulations.

PURPOSE: The accommodation process of the human eye is still a controversial subject. Coleman assumes that the lens, together with the zonula fibers, forms a diaphragm which is held in a catenary shape due to the pressure difference between the aqueous and vitreous body of the lens. The aim of the paper is to compare the results of two simulations (according to the Helmholtz and to the Coleman theories) with ultrasonographic data. METHODS: An axisymmetric static finite element model of the lens was generated using the literature data for geometry, material properties and loads. The refractive power of the lens was calculated for two different ages (29 and 45 years). RESULTS: The application of a pressure to the posterior lens surface did not yield an increase in refractive power change during accommodation. Rather a decrease in accommodation related refractive power was found. CONCLUSIONS: Physiologically relevant refractive power changes are obtained by a simulation in accordance with the Helmholtz theory. A simulation in accordance with the Coleman theory does not yield physiological values of refractive power change.

Accommodation, Ocular↗

PubMed2004

Relation between injected volume and optical parameters in refilled isolated porcine lenses.

PURPOSE: This study was performed to elucidate the correlation between added lens refill material and enhanced lens power as well as the correlation between lens refilling volume and accommodative amplitude as determined by equatorial stretching of ex vivo refilled pigs' lenses. METHODS: Nine porcine lenses were refilled with increasing amounts of silicone oil. After each refill step, the lens power, the lens power change, and the lens thickness were measured both in the relaxed state and with a 3-mm larger ciliary body diameter. In addition, the spherical aberration of the refilled lenses was also quantified. RESULTS: Injection of 0.04 mL silicone material into the relaxed lens enhanced the lens power by 1 D. A 0.54-mm increase of the lens thickness in relaxed lenses added 1 D to the lens power. Increasing the lens refilling volume decreased the lens power changes measured at 3-mm ciliary body stretch. Spherical aberration was positive in the refilled lenses and increased with increasing lens refilling volume. CONCLUSION: The correlation found between the refilling volume and the lens power (0.04 mL D(-1)), as well as the correlation between the lens thickness and the lens power (0.54 mm D(-1)), might be important factors to be controlled in conjunction with surgery, as these also determine the lens power in the presence of this refill material. An increasing lens filling volume is associated with decreasing accommodative amplitude. The positive spherical aberration of refilled porcine lenses presents a sharp contrast to the negative aberration of natural pigs' lenses. Different lens contours and the transition from a gradient to a homogeneous refractive index might be responsible for this change in spherical aberration.

Accommodation, Ocular↗

PubMed2003

Effect of infusion bottle height on lens power after lens refilling with and without a plug.

PURPOSE: To evaluate the influence of intraoperative infusion bottle height on the power of refilled pig lenses. SETTING: Research Laboratory, Pharmacia Intraocular Lens Manufacturing Plant, Groningen, The Netherlands. METHODS: This study comprised 2 groups of pig eyes. In 1 group, the lens was refilled with silicone oil using a plug to close the capsulorhexis; in the other group, no plug was used. The anterior chamber depth, lens thickness, and vitreous chamber depth were measured by A-scan ultrasound. The total refraction was measured with a Hartinger refractometer. Measurements were performed with the infusion bottle at 0 cm, 25 cm, 50 cm, 75 cm, and 100 cm above eye level. Calculations using a model eye were performed to evaluate the change in lens power based on empirical data. RESULTS: The mean change in the power of refilled lenses caused by varying the height of the infusion bottle was 1.8 diopters. Lenses refilled with a plug had a thickness similar to that of natural lenses. Lenses refilled without a plug were significantly thinner (P<.05). The power of lenses refilled with a plug was significantly higher that of lenses refilled without a plug (P<.05). CONCLUSIONS: During lens refilling, infusion bottle height influenced the resulting lens power. Using a plug to close the capsulorhexis resulted in refilled lens dimensions similar to those of the natural lens.

Animals↗

PubMed2003

Polymer refilling of presbyopic human lenses in vitro restores the ability to undergo accommodative changes.

PURPOSE: Because presbyopia is thought to be accompanied by increased lens sclerosis this study was conducted to investigate whether refilling the capsule of the presbyopic human lens with a soft polymer would restore the ability of the lens to undergo accommodative changes. METHODS: Accommodative forces were applied to natural and refilled lenses by circumferential stretching through the ciliary body and zonular complex. Nine natural lenses and 10 refilled lenses from donors ranging in age from 17 to 60 years were studied. Two refill polymers with a different Young's modulus were used. The lens power was measured by a scanning laser ray-tracing technique, and lens diameter and lens thickness were measured simultaneously while the tension on the zonules was increased stepwise by outward pull on the ciliary body. RESULTS: In the natural lenses the older lenses were not able to undergo power changes with stretching of the ciliary body, whereas in the refilled lenses, all lenses showed power changes comparable to young, natural lenses. The refilled human lenses had a higher lens power than the age-matched natural lenses. The Young's modulus of the polymers influenced the lens power change when measured with the ciliary body diameter increased by 4 mm. CONCLUSIONS: Refilling presbyopic lenses with a soft polymer enabled restoration of lens power changes with mechanical stretching. Because sclerosis of the lens is an important factor in human presbyopia, refilling the lens during lens surgery for cataract could enable restoration of clear vision and accommodation in human presbyopia.

Accommodation, Ocular↗

PubMed2002

Monitoring accommodative ciliary muscle function using three-dimensional ultrasound.

BACKGROUND: Our objective was to develop a three-dimensional high-resolution ultrasonic imaging technique to be utilized for in-vivo characterization of the ciliary body and the posterior iris. The benefit of this imaging in enhancing the quantification of the configurational changes in the ciliary body during accommodation is demonstrated. METHODS: Sequential ultrasound biomicroscopic images of the ciliary body region were obtained with a computer-controlled scanning device designed for use with a standard ultrasound biomicroscope for 3D imaging. Custom-made software allows online data collection, data analysis and 3D reconstruction in conjunction with commercially available VoxelView software. RESULTS: The three-dimensional presentation allows a close approximation of the ciliary muscle inside the ciliary body in vivo. We are able to distinguish and to analyze the changes in the muscle contour in different accommodation states. During accommodation a shift in the ciliary muscle center of gravity in a range of 0.04-0.26 mm (mean 0.13+/-0.06 mm) in the direction of the lens equator, with an interindividual variation and a small decrease with age, was observed. CONCLUSIONS: High-resolution ultrasound is a well established technique for in-vivo investigation of the anterior segment. Three-dimensional ultrasound biomicroscopy allows an assessment of the individual ciliary muscle activity in consideration of the ciliary processes. In combination with a contour analysis tool we improved the muscle contour determination during different accommodation states. The investigation showed an activity of the ciliary muscle in young volunteers as well as those of presbyopic age.

Accommodation, Ocular↗