The biomechanical properties of eight human corneas from four normal Chinese fresh corpses were investigated by use of one dimension tensile test, tensile stress relaxation and creep test. The destructive load, stretchy ratio, spreading stress, spreading strain and elastic modulus were determined. Also obtained were the stress relaxation and creep data and curves. After reduction of data, the reduced stress relaxation and creep data and curves were worked out. The regression method was used to get the regression coefficient. The least square method was employed to fit the data of stress and strain; then the stress-strain formula was expressed and the curves of human cornea were plotted. The constitutive equation is K (lambda,t) = G(t) T(e) (lambda) and some conclusions are drawn.
Biomechanical Phenomena ; Cornea ; physiology ; Elastic Modulus ; Humans ; Stress, Mechanical

It is very difficult to measure the human eye properties directly, such as the accommodation mechanism, intraocular pressure distribution, the dynamics of aqueous humor flow and the bio-heat transfer in human eyes. Modeling and simulation may, therefore, play an increasingly important role in the ophthalmologic investigation. The major computer modeling methods, including geometric modeling, physical modeling and mathematical modeling, are introduced in this paper. Modeling and simulation anatomy properties and physiological properties of eye tissues, such as the cornea, aqueous humor and crystalline lens, vitreous, optic nerve head, sclera, are analyzed in the order from global to local, from front to back, from outside to inside. Finally, the problems of computer modeling in ophthalmologic investigation are discussed, and the development trends of the future are pointed out.
Aqueous Humor ; physiology ; Computer Simulation ; Cornea ; physiology ; Eye ; anatomy & histology ; Humans ; Lens, Crystalline ; physiology ; Ophthalmology ; trends ; Sclera ; physiology

A three-dimensional (3D) model of human anterior chamber is reconstructed to explore the effect of different corneal temperatures on the heat transfer in the chamber. Based on the optical coherence tomography imaging of the volunteers with normal anterior chamber, a 3D anterior chamber model was reconstructed by the method of UG parametric design. Numerical simulation of heat transfer and aqueous humor flow in the whole anterior chamber were analyzed by the finite volume methods at different corneal temperatures. The results showed that different corneal temperatures had obvious influence on the temperature distribution and the aqueous flow in the anterior chamber. The temperature distribution is linear and axial symmetrical around the pupillary axis. As the temperature difference increases, the symmetry becomes poorer. Aqueous floated along the warm side and sank along the cool side which forms a vortexing flow. Its velocity increased with the addition of temperature difference. Heat fluxes of cornea, lens and iris were mainly affected by the aqueous velocity. The higher the velocity, the bigger more absolute value of the above-mentioned heat fluxes became. It is practicable to perform the numerical simulation of anterior chamber by the optical coherence tomography imaging. The results are useful for studying the important effect of corneal temperature on the heat transfer and aqueous humor dynamics in the anterior chamber.
Anterior Chamber ; physiology ; Aqueous Humor ; physiology ; Cornea ; physiology ; Humans ; Iris ; Lens, Crystalline ; Models, Biological ; Temperature ; Tomography, Optical Coherence

The pattern and morphology of cellular infiltration of iris melanocytes implanted into the corneal stroma were studied with a rabbit corneal model. Iris melanocytes are transformed into fibroblast-like cells with a loss of pigment granules, which may reflect the in vivo characteristics of iris melanocytes under pathologic conditions. The metaplastic chararter of iris melanocytes appears to be related to the formation of retrocorneal pigmentation and fibrous membrane.
Animals ; Cell Division ; Cornea/*cytology/pathology/surgery ; Iris/*cytology ; Melanocytes/*cytology/physiology/transplantation ; Metaplasia/pathology ; Rabbits

Rigid contact lenses with eccentricity through manufacture can more or less influence visual correction or induce the corneal warpage. Therefore the fine detection of rigid contact lens eccentricity is needed and important. This study was aimed to design a system for lens eccentricity measurement by the principle of optical reflection. By using a standard concave mirror in the center of lens jig, the geometrical center of a lens could be detected accurately. It has solved the problem of lens distortion and breakableness attributed to the conventional method based on rotating reflection. The system is proved to be of practical method with good repeatability.
Contact Lenses ; adverse effects ; Cornea ; pathology ; Refraction, Ocular ; physiology ; Refractive Errors ; pathology

PURPOSE: We investigated the incidence of exposure keratopathy, cornea protective changes in tear film such as corneal sensitivity, tear film stability, and tear secretion after frontalis suspension, and the correlation of these with lagophthalmos. METHODS: The corneal sensitivity test, tear film break-up time (tBUT) measurement, and basic secretion test were performed prospectively in patients who had undergone frontalis suspension. RESULTS: The mean lagophthalmos was highest at postoperative 1 week and then gradually decreased. There were no significant changes in corneal sensitivity, tBUT or tear secretion after surgery. No significant differences were found in those parameters between eyes with lagophthalmos of 3 mm or more and those less than 3 mm, nor did these parameters differ between eyes with clear cornea and exposure keratopathy. Only tBUT at postoperative 1 week was significantly shorter in eyes with lagophthalmos 3 mm or more than those less than 3 mm. The average level of lagophthalmos in eyes with exposure keratopathy (15/33 eyes, 45.4%) was more than 3mm at every follow-up period, which was significantly higher than for eyes with a clear cornea. CONCLUSIONS: Tear physiology tends to maintain normal function despite poor blinking induced by lagophthalmos. The cornea is thought to be protected by these functions of tear film. The factor most influential on cornea status was the level of lagophthalmos, and exposure keratopathy should be carefully examined during postoperative period in eyes with higher lagophthalmos, especially more than 3 mm.
Blinking ; Cornea ; Follow-Up Studies ; Humans ; Incidence ; Physiology ; Postoperative Period ; Prospective Studies ; Tears*

Study of the mechanical properties of in vivo corneal materials is an important basis for further study of corneal physiological and pathological phenomena by means of finite element method. In this paper, the elastic coefficient ( ) and viscous coefficient ( ) of normal cornea and keratoconus under pulse pressure are calculated by using standard linear solid model with the data provided by corneal visualization scheimpflug technology. The results showed that there was a significant difference of and between normal cornea and keratoconus cornea ( < 0.05). Receiver operating characteristic curve analysis showed that the area under curve (AUC) for , and their combined indicators were 0.776, 0.895 and 0.948, respectively, which indicated that keratoconus could be predicted by and . The results of this study may provide a reference for the early diagnosis of keratoconus and avoid the occurrence of keratoconus after operation, so it has a certain clinical value.
Area Under Curve ; Cornea ; physiology ; Elasticity ; Humans ; Keratoconus ; pathology ; ROC Curve ; Viscosity

This study was performed to investigate the corneal epithelial healing time and rate according to the method for promoting the reepithelization after myopic epikeratoplasty. A prospective study was conducted on 30 myopic epikeratoplasties which were divided into 3 groups according to the method for promoting the epithelial healing. The groups consisted of 10 eyes with pressure patches, 10 eyes with Acuvue(R) disposable contact lens (CL) and 10 eyes with SeeQuence(R) disposable CL. The cornea epithelial healing time were 3.4, 3.5 and 3.4 postoperative days for the pressure patch, Acuvue(R) CL and SeeQuence(R) CL groups, respectively. The corneal epithelial healing rates during postoperative 1, 2, and 3 days were 0.33, 0.78, and 0.44 mm2/hour for the pressure patch group; 0.24, 0.92 and 0.37 mm2/hour for the Acuvue(R) CL group; and 0.30, 0.79 and 0.38 mm2/hour for the SeeQuence(R) CL group. These results suggest that a disposable contact lens may not hinder epithelial healing compared with a pressure patch.
Adult ; Bandages ; Contact Lenses ; Cornea/*physiology/surgery ; *Corneal Transplantation ; Epithelium/physiology ; Female ; Humans ; Male ; Middle Aged ; Myopia/*physiopathology/surgery ; Prospective Studies ; Time Factors ; Wound Healing/*physiology

No abstract available.
Child ; Cornea/*abnormalities ; Cysts/*diagnosis ; Eye Abnormalities/*diagnosis ; Eye Diseases/*diagnosis ; Female ; Humans ; Visual Acuity/physiology ; Vitreous Body/*pathology

OBJECTIVE: To explore the relationship between best corrected visual acuity (BCVA) and refraction parameters in myopia. METHODS: Two thousand two hundred and seventy-four patients (4245 eyes) with different degrees of myopia were collected. Their BCVA, diopter of spherical (DS), diopter of cylinder (DC), astigmatism axis, axial length (AL) and corneal thickness were detected. The influence of those parameters on BCVA was studied and the mathematical model of the relationship between BCVA and other parameters including the age and gender of patients was established. RESULTS: The logistic regression analysis showed that there were correlations between the BCVA (y) and DS (x1), DC (x2), gender (x3), AL (x4), corneal thickness (x5), astigmatism axis (x6) and age (x7) (P<0.05): y=0.580 6-0.034 0 x1-0.046 8 x2+0.056 5 x3+0.016 5 x4+ 0.0007 x5+0.000 2 x6-0.005 8 x7. CONCLUSION For people with myopia, age, gender and corneal thickness have small effect on BCVA, while the DS, DC, AL and astigmatism axis have significant effect on BCVA. The BCVA would decline following the extension of DS, DC and AL. It is helpful to assess the vision of myopia by analyzing the refraction parameters comprehensively.
Adolescent ; Adult ; Child ; Cornea/pathology* ; Female ; Forensic Medicine/methods* ; Humans ; Male ; Middle Aged ; Models, Theoretical ; Myopia/physiopathology* ; Refraction, Ocular/physiology* ; Refractometry ; Visual Acuity ; Visual Fields/physiology* ; Young Adult