Finite Element Analysis on Frequency Response of Human Eye under Acoustic Excitation / 医用生物力学

Objective To study the effects of excitation source, intraocular pressure and material parameters on frequency response of human eye under acoustic excitation. Methods Based on the three-dimensional (3D) finite element model of the whole eye, as well as the deformation and stress distribution of human eye, the effects of various parameters on frequency response of human eye were quantitatively analyzed. Results When other parameters were fixed and only the position and size of the excitation source changed, the amplitude at resonance of human eye (the acoustic excitation source was placed directly above the cornea, at an offset of 45°, and at larger excitation) at 134 Hz was 35, 48 and 133 μm, respectively. When only the intraocular pressure changed, the first-order resonance frequency was almost unaffected by the intraocular pressure, and the resonance frequencies of other orders would shift slightly to the left as the intraocular pressure increased. When only the scleral elastic parameters changed, the resonance frequency of eye tissues increased with the increase of the scleral elasticity. Conclusions The position and size of the excitation source have no effects on resonance frequency of human eye, but they have a greater effect on the resonance amplitude. The material parameters of human eye tissues have a greater effect on the frequency response, and there is a linear relationship between the intraocular pressure and resonance frequency. The results provide the theoretical basis for clinical development of high-performance intraocular pressure monitoring technology.

Preliminary establishment of dry eye model in non-obese diabetic mice / 国际眼科杂志(Guoji Yanke Zazhi)

@#AIM:To determine the pathological changes in ocular surfaces dry eye excessive evaporation non-obese diabetic(NOD)mice model and to preliminarily explore the feasibility of diabetic dry eye model.<p>METHODS: In this study, 40 females NOD mice were selected. The experimental group consisted of NOD mice that were diagnosed with diabetes while the normal control group consisted of those NOD mice without spontaneous diabetes. Hypodermic injection of Scopolamine hydrobromide(0.5mg/0.2mL)was administered under 40% humidity to the experimental group and placed in a controlled drying box for 12h a day. This was to achieve a dry eye model. Testing indicators on the 1, 7, 10 and 14d after modeling, phenol red thread test was used to measure tear secretion and the eye sections were stained with periodic acid-Schiff(PAS)to examine the morphology and number of conjunctival goblet cells. On the 10d after modeling, the changes in the corneal epithelium were visualized after staining with hematoxylin. <p>RESULTS:For the NOD mice of the experimental group, the tear secretion was gradually decreased with timing, while there were no obvious changes in the normal control group. The volume of the conjunctival goblet cells of the experimental group became larger, and on the 1d after the molding, the experimental group had decreased density of the goblet cells when compared with the normal control group(<i>P</i>=0.008). From the 7d after the molding, as the time was prolonged, the density of the goblet cells was gradually decreased and the differences between the two group at same time point were significant(all <i>P</i><0.001). Besides, it was required to observe the corneal epithelium of the two groups on the 10d. The result shows that the corneal epithelium became thinned, some epithelial cells were denatured, and stromal cells became edema.<p>CONCLUSION: Dry eye model of NOD mice was preliminary established, and the changes of ocular surface were similar to those of dry eye in the clinic.

Correlations among Refractive Error, Axial Length, and Corneal Power in Childhood

PURPOSE: To investigate sexual differences and correlations among refractive error, axial length (AL), and corneal power. METHODS: A retrospective review of the medical records for 2,006 eyes of children aged 5–16 years was conducted. Cycloplegic refraction and AL measurements were performed on all eyes. Sexual differences in corneal power and AL were investigated in emmetropic eyes and after adjustment for the spherical equivalent (SE). The distribution of AL with every 1 diopter (D) interval was determined. Quantitative correlations among SE, corneal power, and AL were analyzed using multiple regression analyses. RESULTS: The mean age of the subjects was 7.62 years and the mean SE was −0.10 D. Males had a longer AL and lower corneal power than females both in emmetropic eyes and in all subjects after adjustment for the SE. The AL increased 0.40 mm for every −1 D change of the SE. When compared to a 1 D interval of the SE, the AL difference between the upper and lower values of a 95% confidence interval was 2.98 mm, which showed the variability of the AL distribution. Eyes with a long AL had lower corneal power (p < 0.001). Every 1 mm change of AL resulted in a −2.1 D change in the SE, and every 1 D change of corneal power resulted in a −0.8 D change in the SE (p < 0.001). CONCLUSIONS: The distribution of the AL and corneal power was variable, even in eyes with the same refractive error. The AL and corneal power differed by sex. Quantitative correlations between the SE, AL, and corneal power can be clinically used in the estimation of these parameters.

The Feasibility of Short-term Dry Eye Animal Model Using Concanavalin A

PURPOSE: To evaluate the possibility of short-term dry eye model in rabbits by injection of concanavalin A (conA) to the lacrimal and haderian gland of rabbits. METHODS: We injected conA (10 mg/ml, 0.05 ml) to the lacrimal and haderian gland of rabbits twice to induce inflammation of lacrimal gland and compared with saline-injected control by lacrimal gland biopsy with H&E staining for identification of inflammation. The ratio of lacrimal secretion was evaluated by Schirmer test (preinjection vs. postinjection of conA) for 10 days and the number of goblet cells was counted in 10 consecutive high power field using impression cytology with PAS staining. The corneal & conjunctival apoptotic cell deaths were investigated with TUNEL staining 10 days after injection. RESULTS: Infiltration of inflammatory cells and destructed normal architecture of lacrimal gland was found only in conA injected group till 10 days. The Schirmer test showed marked reduction (0.56+/-0.26) by 5days after injection compared with control group (1.07+/-0.35) (p=0.02) and its significant difference was maintained till 10days. The number of goblet cell was 9.70+/-5.03/x200HPF, which was statistically significant decreased compared to control (47.50+/-17.13/x200HPF) at 10 days (p=0.00). Apoptotic cells were increased in injected eye (26.20+/-4.27) compared with those in control (16.60+/-2.70). CONCLUSIONS: Injection of conA to lacrimal glands in rabbit shows decrease of lacrimal secretion and similar cytological changes of the cornea and conjunctiva in human dry eye patients. It suggests its possible feasibility of short-term dry eye animal model for the 10 days.

Eye model for inspecting the functional vision of IOLs / 国际眼科杂志(Guoji Yanke Zazhi)

· AIM: To inspect and compare the functional vision of an aspheric intraocular lens (Tecnis) with those of conventional monofocal silicone and acrylic intraocular lens and multifocal intraocular lens (Array).· METHODS: The IOLs were tested in the eye model, which was designed to be optically equivalent to the theoretical eye model. The eye model is a combination of a spherical photographic lens with 35mm focal length ( IOL put in a water cell)and a charge coupled device (CCD) camera. The images constructed by the lenses are observed on a monitor of personal computer and the contrasts of the images are analyzed by using commercial image processing software.· RESULTS: The modulation transfer function of the eye model equals the scale produced by the theoretical eye model. The images constructed by changing the diameter of aperture stop and IOL.· CONCLUSION: The proposed eye model is useful for testing functional vision and for inspecting differences of intraocular lens.

Geometric changes of the eye with an encircling scleral buckle

PURPOSE: To investigate the postoperative changes and the mechanism of retinal reattachment, the geometric changes of the eye with an encircling scleral buckle was analyzed using a simplified eye model. METHODS: The simplified eye model is an inelastic sphere with an external diameter of 25 mm and an internal diameter of 23.6 millimeters. With an encircling scleral buckle, it was assumed that the circumference of the eyeball would decrease, and in particular with tightening of the buckle, the cross-section of eyeball would be deformed to an ellipsoid shape. The changes in radius, internal surface area, and volume of the eyeball in relationship to the changes in height and span of the silicone buckle were estimated. RESULTS: The radius of eyeball decreased by 0.19-0.90 mm with an encircling scleral buckle, and varied according to the increment of the tightening of the encircling band. The axial length of the eye increased and the volume of the eye decreased also with increased tightening of the band. The scleral arc of the buckle was shorter than the retinal arc of the buckle by 0.09-0.55 mm and the scleral surface area of the buckle was smaller than the retinal area of the buckle by 56-219 mm 2 ; therefore the retina would be redundant. CONCLUSIONS: An encircling scleral buckle changes the axial length and decreases the volume and internal surface area of the eye, making the retina redundant. This redundancy helps resolve or alleviate the problem of a foreshortened retina in retinal reattachment procedures.