Lens Thickness (lens + thickness)

Distribution by Scientific Domains


Selected Abstracts


Effects of hyperglycaemia on ocular development in rabbit: refraction and biometric changes

OPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 2 2005
Peter Herse
Abstract Aim:, To determine the effect of acute and chronic hyperglycaemia on the refraction and development of the rabbit eye. Methods:, Ocular dimensions of five alloxan-induced hyperglycaemic and six control rabbits were measured over 9 weeks using A scan biometry. Refraction was measured using retinoscopy. The animals were 10 weeks of age at the start of the experiment. Results:, The acute onset of hyperglycaemia was associated with a fast and stable 2 D hyperopic shift in refraction. Lens thickness increased during the first 2 weeks of hyperglycaemia, returned to near normal thickness after 3,5 weeks of hyperglycaemia and then decreased in thickness in the last 4 weeks of the study. The hyperopic refraction remained unchanged during changes in lens thickness. Nine weeks of hyperglycaemia was associated with a 25% reduction in the growth of both the globe and the lens and a 17% decrease in body mass compared with the controls. Conclusion:, The hyperopic refraction change of acute hyperglycaemia is likely to be because of a change in the refractive index of the cortical fibres of the lens and is the probable source of the fluctuating refraction seen in diabetic patients. Chronic hyperglycaemia reduced the axial development of the eye and is the probable source of the chronic hyperopic refraction seen in children with Type I diabetes. [source]


Intraocular pressure change after temporal clear corneal phacoemulsification in normal eyes

ACTA OPHTHALMOLOGICA, Issue 1 2010
Inci Irak-Dersu
Abstract. Purpose:, To evaluate short- and long-term intraocular pressure (IOP) changes after temporal clear corneal phacoemulsification in normal eyes. Methods:, The charts of 266 consecutive non-glaucoma patients who underwent uneventful cataract surgery were reviewed. We recorded preoperative and postoperative (1 day, 1 week, 1 month, 3 months, 6 months, 1 year and 2 years) IOP measurements as well as anatomical properties obtained using Zeiss Humphrey IOL Master (Zeiss Meditech, Dublin, California, USA). Results:, Mean IOP reduction after cataract surgery was 8.2%, 4.6%, 6.7% and 7.8% at 3 months, 6 months, 1 year and 2 years, respectively. Lens thickness was the only anatomical characteristic that correlated significantly with IOP decrease after surgery. Conclusion:, Temporal clear corneal phacoemulsification results in a decrease in postoperative IOP that persists for 2 years following surgery. [source]


Refractive error and ocular biometry in Jordanian adults

OPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 4 2005
Edward A. H. Mallen
Abstract The aim of this study was to establish the prevalence of refractive errors in Jordanian adults of working age, and to study the ocular biometric correlates of refractive error in this population. Refractive error and ocular biometry were measured in 1093 Jordanian adult subjects aged 17,40 years to determine the prevalence of refractive error, and explore structural correlations of ametropia. Refractive error was measured using a Grand-Seiko GR-3100K closed-view infrared autorefractor. Ocular component measurements were made using A-scan ultrasonography and autokeratometry. The prevalence of myopia [spherical equivalent refraction (SER) less than ,0.50 DS] and hyperopia (SER greater than +0.50 DS) was 53.71 and 5.67% respectively; 40.62% of the sample was emmetropic (refraction between +0.50 D and ,0.50 D inclusive in both principal meridians). The distribution of SER was found to show marked leptokurtosis, exhibiting a peak between plano and 1 D of myopia. Corneal radius, anterior chamber depth, crystalline lens thickness, vitreous chamber depth and axial length (AL) parameters were normally distributed in the population studied. AL to corneal curvature ratio was not normally distributed, and showed marked leptokurtosis. Linear regression analysis showed that AL correlated most closely with spherical equivalent refractive error. This study has established a database of refractive error prevalence and ocular biometric correlates of ametropia in a Middle Eastern population of working age. [source]


Effects of hyperglycaemia on ocular development in rabbit: refraction and biometric changes

OPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 2 2005
Peter Herse
Abstract Aim:, To determine the effect of acute and chronic hyperglycaemia on the refraction and development of the rabbit eye. Methods:, Ocular dimensions of five alloxan-induced hyperglycaemic and six control rabbits were measured over 9 weeks using A scan biometry. Refraction was measured using retinoscopy. The animals were 10 weeks of age at the start of the experiment. Results:, The acute onset of hyperglycaemia was associated with a fast and stable 2 D hyperopic shift in refraction. Lens thickness increased during the first 2 weeks of hyperglycaemia, returned to near normal thickness after 3,5 weeks of hyperglycaemia and then decreased in thickness in the last 4 weeks of the study. The hyperopic refraction remained unchanged during changes in lens thickness. Nine weeks of hyperglycaemia was associated with a 25% reduction in the growth of both the globe and the lens and a 17% decrease in body mass compared with the controls. Conclusion:, The hyperopic refraction change of acute hyperglycaemia is likely to be because of a change in the refractive index of the cortical fibres of the lens and is the probable source of the fluctuating refraction seen in diabetic patients. Chronic hyperglycaemia reduced the axial development of the eye and is the probable source of the chronic hyperopic refraction seen in children with Type I diabetes. [source]


Cling film as a barrier against CJD in corneal contact A-scan ultrasonography

OPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 1 2003
Asha Rani
Abstract Purpose: To determine the validity of covering a corneal contact transducer probe with cling film as protection against the transmission of Creutzfeldt,Jakob disease (CJD). Methods: The anterior chamber depth, lens thickness and vitreous chamber depth of the right eyes of 10 subjects was recorded, under cycloplegia, with and without cling film covering over the transducer probe of a Storz Omega Compu-scan Biometric Ruler. Measurements were repeated on two occasions. Results: Cling film covering did not influence bias or repeatability. Although the 95% limits of agreement between measurements made with and without cling film covering tended to exceed the intrasessional repeatability, they did not exceed the intersessional repeatability of measurements taken without cling film. Conclusions: The results support the use of cling film as a disposable covering for corneal contact A-scan ultrasonography to avoid the risk of spreading CJD from one subject to another. [source]


From epidemiology to lysyl oxidase like one (LOXL1) polymorphisms discovery: phenotyping and genotyping exfoliation syndrome and exfoliation glaucoma in Iceland

ACTA OPHTHALMOLOGICA, Issue 5 2009
Fridbert Jonasson
Abstract. The first Icelandic articles on exfoliation syndrome (XFS) and exfoliation glaucoma (XFG) appeared some 35 years ago in 1974. Articles since then have included epidemiology, pedigree-based and twin-studies as well as investigations into XFG response to medical therapy and XFS/XFG genetics. All studies found XFS/XFG to be common in Iceland and to be age-related. The Reykjavik Eye Study (RES), a population-based epidemiological study, was first conducted in 1996. The RES found that XFS and XFG prevalence in patients aged 50 years and older was 11% and that XFS/XFG was more common in women than in men. These results were confirmed in 5- and 12-year incidence studies that also suggested that detailed characterization of the phenotype is important, including pupil dilation. In the RES, eyes with XFS were found to be clinically unilateral in about half of cases and to have higher mean intraocular pressure (IOP) than non-XFS eyes. However, XFS was not found to be associated with central corneal thickness, corneal curvature, anterior chamber depth, lens thickness, lens opacification or optic disc morphology. About 15% of persons with XFS had XFG, and XFG eyes had higher risk of developing visual impairment and blindness than eyes with primary open-angle glaucoma. The first genetic studies on Icelanders, conducted about 12 years ago, were linkage studies and were unsuccessful in discovering the genetics behind XFS/XFG. However, in 2007 a genome-wide association study in Iceland using more than 300 000 markers [single nucleotide polymorphisms (SNPs)] on a relatively small number of patients did discover that lysyl oxidase like 1 (LOXL1) on chromosome 15q24 is a major gene for XFS/XFG. These results have now largely been replicated world-wide. [source]


Computerized calculation scheme for retinal image size after implantation of toric intraocular lenses

ACTA OPHTHALMOLOGICA, Issue 1 2007
Achim Langenbucher
Abstract. Purpose., To describe a paraxial computing scheme for tracing an axial pencil of rays through the ,optical system eye' containing astigmatic surfaces with their axes at random. Methods., Two rays (,10 prism diopters from vertical and horizontal) are traced through the uncorrected and corrected eye. In the uncorrected eye one specific ray is selected from the pencil of rays, which passes through the pupil center. In the corrected eye any ray can be traced through the eye. From the slope angle, the intersection of the ray with the refractive surface and the refraction the slope angle of the exiting ray is determined and the ray is traced to the subsequent surface. From both rays traced through the eye an ellipse is fitted to the image to characterize the image distortion of an circular object. Example., Assumptions: target refraction ,0.5,1.0D/A = 90° at 14 mm, corneal refraction 42.5 + 3.5D/A = 15°, axial length 23.6 mm, IOL position 4.6 mm, central lens thickness 0.8 mm, refractive index 1.42, front/back surface of the toric IOL 10.0 D/7.14 + 6.47D/A = 101.8°. The vertical incident ray was imaged to (x, y) = (0.0055 mm, ,1.6470 mm)/(0.0067 mm, ,1.6531 mm) in the uncorrected/corrected eye. The horizontal incident ray was imaged to (x, y) = (1.6266 mm, ,0.0055 mm)/(1.6001 mm, ,0.0067 mm) in the uncorrected/corrected eye. The ellipse (semi-major/semi-minor meridian) fitted to the conjugate image of a circle sized 1.648 mm/1.625 mm in an orientation 14.2° in the uncorrected and 1.654 mm/1.599 mm in an orientation 7.1° in the corrected eye. Conclusion., This concept may be relevant for the assessment of aniseikonia after implantation of toric intraocular lenses for correction of high corneal astigmatism. [source]


Relationships between ocular dimensions and adult stature among participants in the Reykjavik Eye Study

ACTA OPHTHALMOLOGICA, Issue 6 2005
Thor Eysteinsson
Abstract. Purpose:,To examine the relationships between adult stature, age and ocular dimensions in a large homogenous, white population. Methods:,We used the national population census for Reykjavik to select a random sample of adults aged 50 years or older. A total of 846 persons were examined. Scheimpflug images were used to measure anterior chamber depth. Ultrasound was used to measure axial length, lens thickness and vitreous chamber depth. An autorefracto-keratometer was used to measure autorefractive and keratometric values, including the radius of the corneal curvature. Stereo fundus photographs were taken of the optic disc and measurements of the disc diameters were made using computer software. Results:,Height correlated positively with axial length in the multivariate model (B = 0.020, 95% CI 0.006,0.034, p < 0.01). Both age and height showed significant correlations with vitreous chamber depth, where the correlation with age was negative (B = , 0.016, 95% CI , 0.006 to , 0.025, p < 0.005) and the correlation with height was positive (B = 0.019, 95% CI 0.005,0.034, p < 0.01). Height also showed a positive correlation with the radius of the corneal curvature (B = 0.008, 95% CI 0.004,0.011, p < 0.001). Anterior chamber depth had a negative correlation with age (B = , 0.013, 95% CI , 0.010 to , 0.016, p < 0.001), whereas lens thickness had a significant positive correlation with age (B = 0.019, 95% CI 0.016,0.023, p < 0.001). We found a significant negative correlation between axial length and refraction/spherical equivalent (r = , 0.595, p < 0.0001). Discussion:,Our results indicate that there is a significant relationship between height and several ocular dimensions in this adult population and confirms a negative correlation between axial length and refraction. [source]


Association between stature, ocular biometry and refraction in an adult population in rural Myanmar: the Meiktila eye study

CLINICAL & EXPERIMENTAL OPHTHALMOLOGY, Issue 9 2007
Hui Min Wu MD PhD
Abstract Purpose:, To study the association between adult stature and ocular biometric parameters and refraction. Methods:, In a population-based cross-sectional ophthalmic survey of 2418 adults (,40 years old) living in the rural villages in central Myanmar, height and weight were measured using a standardized protocol, and body mass index was calculated. Non-cycloplegic refraction and corneal curvature were determined by an autorefractor. Ultrasound pachymetry was performed and ocular biometry, including axial length, anterior chamber depth, lens thickness and vitreous chamber length were measured using A-mode ocular ultrasonography. Results:, Height and weight were significantly correlated with age, gender and all the ocular biometric parameters, except lens thickness. After adjusting for age and gender, taller and heavier persons had eyes with longer axial length, deeper anterior and vitreous chambers, and flatter and thicker corneas than shorter persons. Height was not significantly correlated with refraction, and heavier persons tended to be less myopic (P < 0.001). Multivariate linear regression models revealed consistent results with the findings for association between height, weight and ocular biometry and refractive error. Conclusions:, Adult stature is independently associated with vitreous chamber length and corneal radius in this Burmese population. Heavier persons were slightly hyperopic. [source]