Determinantes sociales de la salud relacionados con la morbilidad materna extrema departamento de Sucre 2018-2019

Objetivo: Describir los determinantes sociales de la salud relacionados con la aparición de morbilidad materna extrema en gestantes de una institución de salud del departamento de Sucre durante 2018 - 2019. Materiales y métodos: Estudio mixto con fuentes secundarias (Sistema de vigilancia epidemiológica), observación directa en los sitios de residencia y la aplicación de una entrevista semiestructurada al grupo de sobrevivientes. Resultados: La incidencia del evento fue de 1.4 % de gestantes atendidas. El promedio de edad fue de 24 años, pertenece a una etnia el 37.5 %, proceden de área rural el 69.7 %, con niveles educativos bajos (38 %), conviviendo en unión libre (68.7 %), primigestantes (56.2 %), ingreso tardío a los controles prenatales (68.7 %), promedio de asistencias de 3.5 controles. Los determinantes que guardan relación estadística para la aparición del evento fueron: nivel educativo, la pertenencia étnica, tenencia de compañero sentimental y número de controles a los que asiste. La calidad de los servicios de salud, la pobreza, inaccesibilidad geográfica y barreras administrativas de las aseguradoras fueron las más destacadas para las gestantes. Conclusión: El evento se presenta principalmente en gestantes jóvenes, con bajo nivel educativo y de zonas rurales, los determinantes que se asociaron fueron: la etnia, el número de controles prenatales a los que asiste, el nivel educativo y el estado conyugal; para las gestantes con Morbilidad materna los bajos ingresos económicos, la inaccesibilidad a los servicios de salud y la mala calidad en la prestación de estos fueron los más importantes.

Objective: To describe the social determinants of health related to the appearance of extreme maternal morbidity in pregnant women from a health institution in the department of Sucre, for the 2018 - 2019 period. Materials and methods: Mixed study with secondary sources (Epidemiological surveillance system), direct observation at the places of residence, and the application of a semi-structured interview to the group of survivors. Results: The incidence of the event was 1.4% of pregnant women attending. The average age was 24 years old, 37.5% belong to an ethnic group, 69.7% from rural areas, with low educational levels (38%), living together in a free union (68.7%), first pregnancy (56.2%), late admission to prenatal controls (68.7%), average attendance of 3.5 controls. The determinants that are statistically related to the occurrence of the event were: educational level, ethnicity, possession of a romantic partner, and number of controls attended. The quality of health services, poverty, geographic inaccessibility, and administrative barriers of insurance companies were the most prominent for pregnant women. Conclusion: The event occurs mainly in young pregnant women, with a low educational level, and in rural areas. The determinants that were associated were: ethnicity, the number of prenatal check-ups attended, educational level, and marital status; for pregnant women with maternal morbidity, low income, inaccessibility to health services, and the presence of previous illnesses were the most important.

Caracterización de la prestación del servicio farmacéutico en el departamento de Sucre, Colombia / Characterization of the provision of the pharmaceutical service in the department of Sucre, Colombia

RESUMEN Con la ejecución de este estudio se pretende evaluar el nivel de cumplimiento de los servicios farmacéuticos del departamento de Sucre con las condiciones esenciales y procedimientos establecidos en la normatividad legal vigente en el país, así como determinar las características de la prestación de este servicio. Para lo cual, se realizó un estudio descriptivo exploratorio. Primero se solicitó el censo de establecimientos farmacéuticos del departamento de Sucre a la Secretaría Departamental de Salud y Cámara de Comercio, y fue seleccionado una muestra de servicios farmacéuticos dependientes e independientes por municipios, posteriormente se diseñó una herramienta de verificación basada en los requisitos exigidos por la Resolución 1403 de 2007, la cual fue aplicada en los sitios seleccionados. En el departamento de Sucre, el 99,47% de los servicios farmacéuticos se encuentran ubicados en zonas urbanas, la prestación del servicio es predominantemente independiente, la dirección técnica es ejercida en su mayoría por químicos farmacéuticos. En cuanto al nivel de cumplimiento, los servicios farmacéuticos dependientes presentan un 70,21% de cumplimiento y los independientes, 49,61%. En conclusión, se evidencia un problema de acceso a los medicamentos en las zonas rurales y una alta proporción de servicios farmacéuticos que no hacen parte del Sistema General de Seguridad Social en Salud, además de falencias en cuanto al nivel de cumplimiento sobre todo en los servicios independientes, lo cual genera una gran preocupación y la necesidad de generar acciones conjuntas entre las universidades, IPS, EPS y Gobierno para garantizar el acceso, la calidad y el uso adecuado de los medicamentos.

SUMMARY The objective of this study is to evaluate the level of compliance of the pharmaceutical services of the Department of Sucre with the essential conditions and procedures established in the legal regulations in the country, as well as to determine the characteristics of the provision of this service. For which, an exploratory descriptive study was carried out. First, a census of pharmaceutical establishments from the department of Sucre was requested from the Departmental Secretary of Health and the Chamber of Commerce, and a sample of dependent and independent pharmaceutical services by municipalities was selected, after which a verification tool was designed based on the requirements demanded by Resolution 1403 of 2007, which was applied in the selected sites. In the Department of Sucre, 99.47% of pharmaceutical services are located in urban areas, the service is predominantly independent and the technical direction is exercised mostly by pharmaceutical chemists. Regarding the compliance level, the dependent pharmaceutical services have 70.21% compliance and the independent 49.61%. In conclusion, there is evidence of a problem of access to medicines in rural areas and a high proportion of pharmaceutical services that are not part of the General System of Social Security in Health, in addition to shortcomings in the level of compliance especially in independent services, which generates great concern and the need to generate joint actions among universities, IPS, EPS and government to guarantee access, quality and proper use of medicines.

Distortion correction of OCT images of the crystalline lens: gradient index approach.

PURPOSE: To propose a method to correct optical coherence tomography (OCT) images of posterior surface of the crystalline lens incorporating its gradient index (GRIN) distribution and explore its possibilities for posterior surface shape reconstruction in comparison to existing methods of correction. METHODS: Two-dimensional images of nine human lenses were obtained with a time-domain OCT system. The shape of the posterior lens surface was corrected using the proposed iterative correction method. The parameters defining the GRIN distribution used for the correction were taken from a previous publication. The results of correction were evaluated relative to the nominal surface shape (accessible in vitro) and compared with the performance of two other existing methods (simple division, refraction correction: assuming a homogeneous index). Comparisons were made in terms of posterior surface radius, conic constant, root mean square, peak to valley, and lens thickness shifts from the nominal data. RESULTS: Differences in the retrieved radius and conic constant were not statistically significant across methods. However, GRIN distortion correction with optimal shape GRIN parameters provided more accurate estimates of the posterior lens surface in terms of root mean square and peak values, with errors <6 and 13 µm, respectively, on average. Thickness was also more accurately estimated with the new method, with a mean discrepancy of 8 µm. CONCLUSIONS: The posterior surface of the crystalline lens and lens thickness can be accurately reconstructed from OCT images, with the accuracy improving with an accurate model of the GRIN distribution. The algorithm can be used to improve quantitative knowledge of the crystalline lens from OCT imaging in vivo. Although the improvements over other methods are modest in two dimension, it is expected that three-dimensional imaging will fully exploit the potential of the technique. The method will also benefit from increasing experimental data of GRIN distribution in the lens of larger populations.

Contribution of the crystalline lens gradient refractive index to the accommodation amplitude in non-human primates: in vitro studies.

The purpose of this study was to determine the contribution of the gradient refractive index to the change in lens power in hamadryas baboon and cynomolgus monkey lenses during simulated accommodation in a lens stretcher. Thirty-six monkey lenses (1.4-14.1 years) and twenty-five baboon lenses (1.8-28.0 years) were stretched in discrete steps. At each stretching step, the lens back vertex power was measured and the lens cross-section was imaged with optical coherence tomography. The radii of curvature for the lens anterior and posterior surfaces were calculated for each step. The power of each lens surface was determined using refractive indices of 1.365 for the outer cortex and 1.336 for the aqueous. The gradient contribution was calculated by subtracting the power of the surfaces from the measured lens power. In all lenses, the contribution of the surfaces and gradient increased linearly with the amplitude of accommodation. The gradient contributes on average 65 ± 3% for monkeys and 66 ± 3% for baboons to the total power change during accommodation. When expressed in percent of the total power change, the relative contribution of the gradient remains constant with accommodation and age in both species. These findings are consistent with Gullstrand's intracapsular theory of accommodation.

Semiautomated analysis of optical coherence tomography crystalline lens images under simulated accommodation.

Presbyopia is an age related, gradual loss of accommodation, mainly due to changes in the crystalline lens. As part of research efforts to understand and cure this condition, ex vivo, cross-sectional optical coherence tomography images of crystalline lenses were obtained by using the Ex-Vivo Accommodation Simulator (EVAS II) instrument and analyzed to extract their physical and optical properties. Various filters and edge detection methods were applied to isolate the edge contour. An ellipse is fitted to the lens outline to obtain central reference point for transforming the pixel data into the analysis coordinate system. This allows for the fitting of a high order equation to obtain a mathematical description of the edge contour, which obeys constraints of continuity as well as zero to infinite surface slopes from apex to equator. Geometrical parameters of the lens were determined for the lens images captured at different accommodative states. Various curve fitting functions were developed to mathematically describe the anterior and posterior surfaces of the lens. Their differences were evaluated and their suitability for extracting optical performance of the lens was assessed. The robustness of these algorithms was tested by analyzing the same images repeated times.

Postnatal elongation of eye size in DBA/2J mice compared with C57BL/6J mice: in vivo analysis with whole-eye OCT.

PURPOSE: To characterize postnatal changes in eye size in glaucomatous DBA/2J (D2) mice and in nonglaucomatous C57BL/6J mice (B6) in vivo by means of whole-eye optical coherence tomography (OCT). METHODS: D2 (n = 32) and B6 (n = 36) mice were tested between 2 and 20 months of age in eight age bins. A custom time-domain OCT system with a center wavelength of 825 nm and an axial scan length of 7.1 mm produced axial A-scan interferograms at a rate of 20 A-lines/s with a resolution of 8 µm. Axial length (AL), corneal thickness (CT), anterior chamber depth (ACD), lens thickness (LT), vitreous chamber depth (VCD), and retinal thickness (RT) were measured in the optical axis and adjusted with corresponding refractive indices. Corneal curvature (CC) and IOP were also measured. RESULTS: AL increased (P < 0.001) more in the D2 (21%) than in the B6 (9%) mice. There was an interaction effect (two-way ANOVA, P < 0.001) between age and strain for AL, CT, ACD, and VCD. In the D2 mice, the lens became dislocated posteriorly. Multiple regression analysis in the D2 mice revealed an independent effect of age and IOP (P ≤ 0.01) on axial length. CC steepened in the older D2 mice, whereas it flattened in the B6 mice. CONCLUSIONS: In D2 mice, postnatal elongation of AL is larger than that in B6 mice and is associated with a greater increase in ACD and IOP, which seems to be a causal factor. The ease of use, short acquisition time, and noninvasiveness of whole-eye OCT make it suitable for routine use in longitudinal studies of mouse models.

Age-dependent variation of the Gradient Index profile in human crystalline lenses.

PURPOSE: To reconstruct the gradient index (GRIN) profile of human crystalline lenses ex-vivo using Optical Coherence Tomography (OCT) imaging with an optimization technique and to study the dependence of the GRIN profile with age. METHODS: Cross-sectional images of nine isolated human crystalline lenses with ages ranging from 6 to 72 (post mortem time 1 to 4 days) were obtained using a custom-made OCT system. Lenses were extracted from whole cadaver globes and placed in a measurement chamber filled with preservation medium (DMEM). Lenses were imaged with the anterior surface up and then flipped over and imaged again, to obtain posterior lens surface profiles both undistorted and distorted by the refraction through the anterior crystalline lens and GRIN. The GRIN distribution of the lens was described with three variables by means of power function, with variables being the nucleus and surface index, and a power coefficient that describes the decay of the refractive index from the nucleus to the surface. An optimization method was used to search for the parameters that produced the best match of the distorted posterior surface. RESULTS: The distorted surface was simulated with accuracy around the resolution of the OCT system (under 15 µm). The reconstructed refractive index values ranged from 1.356 to 1.388 for the surface, and from 1.396 to 1.434 for the nucleus. The power coefficient ranged between 3 and 18. The power coefficient increased significantly with age, at a rate of 0.24 per year. CONCLUSION: Optical Coherence Tomography allowed optical, non-invasive measurement of the 2-D gradient index profile of the isolated human crystalline lens ex vivo. The age-dependent variation of the changes is consistent with previous data using magnetic resonance imaging, and the progressive formation of a refractive index plateau.

Refractive power and biometric properties of the nonhuman primate isolated crystalline lens.

Purpose. To characterize the age dependence of shape, refractive power, and refractive index of isolated lenses from nonhuman primates. Methods. Measurements were performed on ex vivo lenses from cynomolgus monkeys (cyno: n = 120; age, 2.7-14.3 years), rhesus monkeys (n = 61; age, 0.7-13.3 years), and hamadryas baboons (baboon: n = 16; age, 1.7-27.3 years). Lens thickness, diameter, and surface curvatures were measured with an optical comparator. Lens refractive power was measured with a custom optical system based on the Scheiner principle. The refractive contributions of the gradient, the surfaces, and the equivalent refractive index were calculated with optical ray-tracing software. The age dependence of the optical and biometric parameters was assessed. Results. Over the measured age range isolated lens thickness decreased (baboon: -0.04, cyno: -0.05, and rhesus: -0.06 mm/y) and equatorial diameter increased (logarithmically for the baboon and rhesus, and linearly for cyno: 0.07 mm/y). The isolated lens surfaces flattened and the corresponding refractive power from the surfaces decreased with age (-0.33, -0.48, and -0.68 D/y). The isolated lens equivalent refractive index decreased (only significant for the baboon, -0.001 D/y), and as a result the total isolated lens refractive power decreased with age (baboon: -1.26, cyno: -0.97, and rhesus: -1.76 D/y). Conclusions. The age-dependent trends in the optical and biometric properties, growth, and aging, of nonhuman primate lenses are similar to those of the pre-presbyopic human lens. As the lens ages, the decrease in refractive contributions from the gradient refractive index causes a rapid age-dependent decrease in maximally accommodated lens refractive power.

Distortions of the posterior surface in optical coherence tomography images of the isolated crystalline lens: effect of the lens index gradient.

We quantify the posterior surface distortions in optical coherence tomography (OCT) images of isolated crystalline lenses. The posterior radius of curvature and asphericity obtained from OCT images acquired with the beam incident first on the anterior, and then the posterior, surface were compared. The results were compared with predictions of a ray-tracing model which includes the index gradient. The results show that the error in the radius of curvature is within the measurement reproducibility and that it can be corrected by assuming a uniform refractive index. However, accurate asphericity values require a correction algorithm that takes into account the gradient.

Effect of anterior zonule transection on the change in lens diameter and power in cynomolgus monkeys during simulated accommodation.

PURPOSE: To quantify the role of anterior zonular tension on the optomechanical lens response during simulation of accommodation in primates. METHODS: Postmortem cynomolgus monkey eyes (n = 14; age range, 3.0-11.5 years) were dissected leaving intact the lens, zonules, ciliary body, hyaloid membrane, anterior vitreous, and a scleral rim. The lens was mounted in a lens-stretching system and stretched radially in step-wise fashion. The load, and the lens diameter and power were measured at each step and the diameter- and power-load relationships were quantified. The anterior zonular fibers were then transected, and the experiment was repeated. The equatorial lens diameter and lens optical power before and after zonular transection were compared. RESULTS: Stretching increased the lens diameter by 0.25 +/- 0.09 mm (median +/- interquartile range) before and 0.25 +/- 0.19 mm after zonular transection. Stretching decreased the lens power by 13.0 +/- 6.5 D before and 10.6 +/- 8.0 D after zonular transection. The load required to change the diameter of the lens by 1 mm decreased from 18.8 +/- 10.7 g before to 15.0 +/- 7.8 g after zonular transection. The absolute change in power per gram of loading decreased from 2.5 +/- 1.1 before to 2.0 +/- 1.2 D after zonular transection. CONCLUSIONS: The cynomolgus monkey lens retains a significant fraction of its accommodative ability after transection of the anterior zonules in simulated accommodation experiments.

Shape of the isolated ex-vivo human crystalline lens.

PURPOSE: To develop an age-dependent mathematical model of the isolated ex-vivo human crystalline lens shape to serve as basis for use in computational modeling. METHODS: Profiles of whole isolated human lenses (n=27) aged 6 to 82, were measured from shadow-photogrammetric images. Two methods were used to analyze the lenses. In the two curves method (TCM) the anterior and posterior surfaces of the lens were fit to 10th-order even polynomials and in the one curve method (OCM) the contour of one half-meridional section of the lens was fit to 10th-order polynomials. The age-dependence of the polynomial coefficients was assessed. The analysis was used to produce an age-dependent polynomial model of the whole lens shape. RESULTS: The root mean squared errors for the fits ranged from 11 to 70 microm for the OCM, 9 to 27 microm for the posterior surface of the TCM and 8 to 134 microm for the anterior surface of the TCM. The coefficients of the OCM did not display a significant trend with age. The 2nd-, 6th- and 10th-order coefficients of the anterior surface of the TCM decreased with age while the 8th-order coefficient increased. For the posterior surface of the TCM, the 8th-order coefficient significantly decreased with age and the 10th-order coefficient increased. The age-dependent equations of both the models provide a reliable model from age 20 to 60. The OCM model can be used for lenses older than 60 as well. CONCLUSION: The shape of the whole human crystalline lens can be accurately modeled with 10th-order polynomial functions. These models can serve to improve computational modeling, such as finite element (FE) modeling of crystalline lenses.

Refractive index measurement of the isolated crystalline lens using optical coherence tomography.

An optical coherence tomography system has been developed that was designed specifically for imaging the isolated crystalline lens. Cross-sectional OCT images were recorded on 40 lenses from 32 human donors with an age range of 6-82 years. A method has been developed to measure the axial thickness and average refractive index of the lens from a single recorded image. The measured average group refractive index at the measurement wavelength of 825 nm was converted to the average phase refractive index at 589 nm using lens dispersion data from the literature. The average refractive index for all lenses measured was 1.408+/-0.005 which agrees well with recent MRI measurements of the lens index gradient. A linear regression of the data resulted in a statistically significant decrease in the average refractive index with age, but a simple linear model was insufficient to explain the age dependence. The results presented here suggest that the peak refractive index in the nucleus is closer to 1.420, rather than the previously accepted value of 1.406.

Role of the lens capsule on the mechanical accommodative response in a lens stretcher.

PURPOSE: To determine whether changes in elastic properties of the lens capsule ex vivo with age contribute to the forces necessary for accommodation. METHODS: Postmortem human (n = 22; age average: 41 +/- 17 years; range: 6-7) and cynomolgus monkey (n = 19; age average: 7.7 +/- 1.8 years, range: 4.2-10) tissues including the lens, capsule, zonules, ciliary body, and sclera were mounted in an optomechanical lens-stretching system. Starting at 0 load, the sclera was symmetrically stretched to 2 mm in 0.25-mm steps at a speed of 0.1 mm x s(-1). The load and lens diameter were measured at each step. The lens contents were removed through a mini-capsulorhexis. The stretching cycles were repeated on the empty capsular bag. The forces necessary to stretch the natural lens and empty bag were quantified as a function of age and compared. RESULTS: The force needed to stretch the empty lens capsule was independent of age (human, 2.6-34.9 g/mm [25.2-342.7 mN/mm]; monkey, 8.2-21.3 g/mm [80.3-208.6 mN/mm]). The ratio of the force necessary to stretch the empty lens capsule to the force necessary to stretch the natural lens decreased with age in the human and monkey lenses (P = 0.003, P = 0.72, respectively). CONCLUSIONS: The mechanical properties of the empty lens capsule assessed ex vivo in a lens stretcher remain constant with age, suggesting that the changes in elasticity of the lens capsule do not play a significant role in presbyopia. In young eyes, the lens capsule determines the force necessary to stretch the whole lens. The age-related increase in force needed to stretch the lens is due to changes in the lens contents.

Optical power of the isolated human crystalline lens.

PURPOSE: To characterize the age dependence of isolated human crystalline lens power and quantify the contributions of the lens surfaces and refractive index gradient. METHODS: Experiments were performed on 100 eyes of 73 donors (average 2.8 +/- 1.6 days postmortem) with an age range of 6 to 94 years. Lens power was measured with a modified commercial lensmeter or with an optical system based on the Scheiner principle. The radius of curvature and asphericity of the isolated lens surfaces were measured by shadow photography. For each lens, the contributions of the surfaces and the refractive index gradient to the measured lens power were calculated by using optical ray-tracing software. The age dependency of these refractive powers was assessed. RESULTS: The total refractive power and surface refractive power both showed a biphasic age dependency. The total power decreased at a rate of -0.41 D/y between ages 6 and 58.1, and increased at a rate of 0.33D/y between ages 58.1 and 82. The surface contribution decreased at a rate of -0.13 D/y between ages 6 and 55.2 and increased at a rate of 0.04 D/y between ages 55.2 and 94. The relative contribution of the surfaces increased by 0.17% per year. The equivalent refractive index also showed a biphasic age dependency with a decrease at a rate of -3.9 x 10(-4) per year from ages 6 to 60.4 followed by a plateau. CONCLUSIONS: The lens power decreases with age, due mainly to a decrease in the contribution of the gradient. The use of a constant equivalent refractive index value to calculate lens power with the lens maker formula will underestimate the power of young lenses and overestimate the power of older lenses.

Optomechanical response of human and monkey lenses in a lens stretcher.

PURPOSE: To quantify the forces necessary to change the shape and optical power of human and monkey lenses. METHODS: Cynomolgus monkey (n = 48; age: 3.8-11 years), rhesus monkey (n = 35; age: 0.7-17 years) and human (n = 20, age 8-70 years) eyes obtained postmortem, including the lens, capsule, zonules, ciliary body, and sclera were mounted in an optomechanical lens-stretching system. Starting at zero load, the lenses were symmetrically stretched in a stepwise fashion in 0.25- or 0.5-mm steps. The load, lens diameter, inner ciliary body diameter, and lens power were measured at each step and the diameter- and power-load responses were quantified. RESULTS: The diameter- and power-load responses were found to be linear in the physiologically relevant range of stretching. The average change in cynomolgus, rhesus, and human lens diameter, respectively, was 0.094, 0.109, and 0.069 mm/g in young lenses, and 0.069, 0.067, and 0.036, mm/g in older lenses. For the same lenses, the average change in lens power was -3.73, -2.83, and -1.22 D/g in young lenses and -2.46, -2.16, and -0.49 D/g in older lenses. CONCLUSIONS: The force necessary to change the lens diameter and lens power increases with age in human and monkey lenses. The results agree with the Helmholtz theory of accommodation and with presbyopia theories that predict that the force required to disaccommodate the lens increases with age.

Biometry of primate lenses during immersion in preservation media.

PURPOSE: The purpose of this study was to assess the condition of human lenses (obtained from an eye bank) and of fresh monkey lenses, and to determine the effects of maintaining these lenses in various liquid preservation media. METHODS: Freshly excised human and monkey lenses were maintained for 5 h in one of four solutions (Balanced Saline Solution [BSS], Ringer's Solution, Dulbecco's Modified Eagle Medium with Ham's F-12 [DMEM/F-12/F-12], and Tissue Culture Medium 199 [TC-199]) using a custom-designed, temperature-regulated testing cell. A modified optical comparator and digital camera were used to photograph magnified lens profiles and measure lens diameter and thickness. Lens volume was then calculated assuming rotational symmetry about the optical axis. RESULTS: Seven of the 33 human lenses exhibited extensive swelling and separation of the capsule from the lens cell mass prior to the incubation. During incubation, for 12/22 of the remaining human and 27/27 of the monkey lenses, thickness increased by 1.0-1.8%, diameter decreased by 0.7-1.6% and the volume was essentially unchanged. Substantial swelling and capsular separation were observed in 10 of the 22 human lenses, 7/10 for those maintained in salt solutions, and 3/12 for those in tissue culture media. Lens volumes increased by an average of 6.8%, due to an 8.7% increase in the thickness, while the diameter decreased by 0.9%. These changes appeared to be independent of postmortem time and donor age. CONCLUSIONS: Culture media are more effective than simple salt solutions in maintaining lens physical integrity during short-term incubations. Substantial uptake of water, accompanied by separation of the capsule from the lens cell mass, occurs at various stages during storage and experimental manipulations in >60% of human lenses obtained from the eye bank. Data obtained with such lenses will not be representative of the true ex vivo state. It is recommended that lenses be assessed to determine if swelling has taken place before acceptance of data.

In vitro dimensions and curvatures of human lenses.

The purpose of this study was to determine dimensions and curvatures of excised human lenses using the technique of shadowphotogrammetry. A modified optical comparator and digital camera were used to photograph magnified sagittal and coronal lens profiles. Equatorial diameter, anterior and posterior sagittal thickness, anterior and posterior curvatures, and shape factors were obtained from these images. The data were used to calculate lens volumes, which were compared with the lens weights. Measurements were made on 37 human lenses ranging in age from 20 to 99 years. These showed that lens dimensions and the anterior radius of curvature increase linearly throughout adult life while posterior curvature remains constant. The relative shape (or aspect ratio) of the posterior lens is unchanged through adult life since both equatorial diameter and posterior thickness increase at the same rate. The ratio of anterior thickness to posterior thickness is constant at 0.70. It is suggested that in vivo forces alter the apparent location of the lens equator, that the in vitro lens shape corresponds to the maximally accommodated shape in vivo and that the shapes of the accommodated and unaccommodated lens progressively converge toward each other due to lens growth with age, with a convergence point located near the age of total loss of accommodation (55-60 years). Together, these observations provide additional support for the Helmholtz theory of accommodation.

Preparation and hydration control of corneal tissue strips for experimental use.

PURPOSE: The purpose of this study was to develop an experimental protocol to maintain corneal tissue strips at normal hydration and avoid swelling or dehydration during experimental studies on corneal biomechanics and thermal stability. METHODS: The corneal thickness of 9 whole Eye-Bank eyes was brought back to normal values by immersion in a 25% dextran solution for 24 hours. Corneal buttons were then removed and cut into 2 x 6 mm strips. The 9 strips were immersed successively in Dextran solutions at 25%, 22.5%, and 20% concentration at 35 degrees C. The thickness of the immersed strip in solution was measured every 5 minutes for 1 hour using a modified optical comparator. RESULTS: The mean final thickness for the nine corneal strips after one hour in 25%, 22.5%, and 20% dextran solution was 508 +/- 38, 563 +/- 56, and 592 +/- 33 microm, respectively. Average swelling in 25%, 22.5%, and 20% dextran solutions was 1.06 +/- 0.03, 1.20 +/- 0.07, and 1.24 +/- 0.07 times the initial thickness, respectively. CONCLUSION: The hydration of corneal tissue strips is maintained at normal values when the strips are immersed in 25% Dextran solution. Corneal strips swell to thicknesses above normal values in solutions with lower molecular weights.

Semianalytical thermal model for subablative laser heating of homogeneous nonperfused biological tissue: application to laser thermokeratoplasty.

We present a semianalytical technique to calculate the temperature in homogeneous nonperfused tissue during subablative laser heating. Analytical expressions of the temperature distribution in time and space are provided for collimated beams with Gaussian and top-hat intensity distributions perpendicularly incident on a finite tissue slab. The temperature distribution produced with a collimated Gaussian beam is the triple sum of the product of four functions of separate variables. The semianalytical technique can be used to rapidly calculate the temperature in laser-irradiated tissue at any point in time and space. The model was used to estimate the corneal temperature during pulsed holmium:YAG laser thermokeratoplasty with various boundary conditions at the anterior and posterior corneal surface. The model demonstrates that the corneal temperature during laser thermokeratoplasty (LTK) with a pulsed Ho:YAG laser may be sufficient to induce superficial vaporization of epithelial cells and local thermal damage to the endothelium. The calculations show that convection at the anterior corneal surface does not have a significant effect on the corneal temperature distribution, but that a better knowledge of the cooling effect of the aqueous is required to better estimate the corneal temperature distribution during LTK.