Journal ArticleDOI
Improvements on Littmann's method of determining the size of retinal features by fundus photography.
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TLDR
Three new methods of determining Littmann's factor q become available: simply reducing the axial length by a constant 1 · 82 mm; constructing a personalized schematic eye, given additional data; and ray tracing through this eye to extend calculations to peripheral retinal areas.Abstract:
Littmann's formula relating the size of a retinal feature to its measured image size on a telecentric fundus camera film is widely used. It requires only the corneal radius, ametropia, and Littmann's factor q obtained from nomograms or tables. These procedures are here computerized for practitioners' convenience. Basic optical principles are discussed, showing q to be a constant fraction of the theoretical ocular dimension k′, the distance from the eye's second principal point to the retina. If the eye's axial length is known, three new methods of determining q become available: (a) simply reducing the axial length by a constant 1 · 82 mm; (b) constructing a personalized schematic eye, given additional data; (c) ray tracing through this eye to extend calculations to peripheral retinal areas. Results of all these evaluations for 12 subjects of known ocular dimensions are presented for comparison. Method (a), the simplest, is arguably the most reliable. It shows good agreement with Littmann's supplementary procedure when the eye's axial length is known.read more
Citations
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Journal ArticleDOI
Prevalence of fundus tessellation and its associated factors in Chinese children and adolescents with high myopia.
Tianyu Cheng,Junjie Deng,Xian Xu,Bo Zhang,Jingjing Wang,Shuyu Xiong,Yuchen Du,Suqin Yu,Wei Gong,Huijuan Zhao,Mengli Luan,Ying Fan,Jianfeng Zhu,Haidong Zou,Xun Xu,Xiangui He +15 more
TL;DR: In this article, the authors investigated the prevalence and associated factors of fundus tessellation in highly myopic children and adolescents, and a novel grading approach was adopted to classify fundus Tessellations into four categories on colour fundus photography, referring to the location of tesselation divided by an Early Treatment Diabetic Retinopathy Study grid centred on the fovea.
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Normative values of retinal vessel oximetry in healthy children against adults.
TL;DR: The aim of this study was to compare the RO parameters of healthy children to those in adults, and to establish a baseline level of confidence for this method in adults.
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Comparison of Individual Retinal Layer Thicknesses between Highly Myopic Eyes and Normal Control Eyes Using Retinal Layer Segmentation Analysis.
Jin Hyung Kim,Sung Hoon Lee,Jae Yong Han,Hyun Goo Kang,Suk Ho Byeon,Sung Soo Kim,Hyoung Jun Koh,Sung Chul Lee,Min Kim +8 more
TL;DR: Axially elongated, non-pathologic highly myopic eyes had different structural features than control eyes, with significantly greater individual macular layer thicknesses independent of sex or age.
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Macular Thickness, Foveal Volume, and Choroidal Thickness in Amblyopic Eyes and Their Relationships to the Treatment Outcome
TL;DR: The initial severity of amblyopia and the type of Amblyopia were the risk factors related to the poor outcome of ambleyopic treatment and thefoveal thickness, foveal volume, and choroidal thickness were not associated with the treatment outcome.
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The influence of axial length on confocal scanning laser ophthalmoscopy and spectral-domain optical coherence tomography size measurements: a pilot study
TL;DR: The present findings demonstrate accuracy of the scaling in cSLO and SD-OCT measurements of the Heidelberg Spectralis for emmetropic medium eyes.
References
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Journal ArticleDOI
Determination of the real size of an object on the fundus of the living eye
TL;DR: A method is described which allows the real diameter of an object on the fundus to be determined by means of a system of curves which are the result of trigonometrical calculations and which give an approximate value.
Book
Clinical Visual Optics
TL;DR: The eye's optical system visual acuity and contrast sensitivity spherical ametropia astigmatism subjective refraction accommodation and near vision ocular motility and binocularVision convergence anomalies of binocular vision - heterophoria and heterotropia stereopsis and the stereoscope.
Journal ArticleDOI
Determining the true size of an object on the fundus of the living eye
TL;DR: The result was represented by curves which enable factors used in calculating the true diameter to be determined, but instead of the curves a quadratic equation is used to produce the same factors.
Journal ArticleDOI
A method of determining the equivalent powers of the eye and its crystalline lens without resort to phakometry
TL;DR: If the positions of the principal points of the crystalline lens are conjectured, its equivalent power and that of the eye can be calculated as described from ocular dioptrics.