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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The effect of axial length on laser spot size and laser irradiance.
TL;DR: The effect of axial length on laser spot size and laser irradiance may be ignored when administering photodynamic therapy with verteporfin but has to be considered for transpupillary thermal treatment of choroidal neovascular lesions.
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Prevalence of myopic retinopathy in rural Central India.
Jost B. Jonas,Vinay Nangia,Rajesh Gupta,Krishna Bhojwani,Prabhat Nangia,Songhomitra Panda-Jonas +5 more
TL;DR: In this paper, the prevalence of myopic retinopathy (MR) in rural Central India was determined, and a binary regression analysis was used to identify the most likely individuals with MR.
Journal ArticleDOI
Age-related changes of individual macular retinal layers among Asians.
Jacqueline Chua,Yih Chung Tham,Bingyao Tan,Kavya Devarajan,Florian Schwarzhans,Alfred Tau Liang Gan,Damon Wong,Carol Y. Cheung,Shivani Majithia,Sahil Thakur,Georg Fischer,Clemens Vass,Ching-Yu Cheng,Leopold Schmetterer +13 more
TL;DR: Most of the retinal layers decreased with age except for foveal retinal nerve fiber layer (RNFL) and the inner/outer segments of photoreceptors where they increased with age.
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Measurement of normal optic nerve head parameters.
TL;DR: Recent data on the normal morphology and measurement of optic nerve head parameters as assessed by the major imaging modalities now available are summarized.
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Objective Assessment of Foveal Cone Loss Ratio in Surgically Closed Macular Holes Using Adaptive Optics Scanning Laser Ophthalmoscopy
Satoshi Yokota,Sotaro Ooto,Masanori Hangai,Kohei Takayama,Naoko Ueda-Arakawa,Yoshihara Yuki,Masaaki Hanebuchi,Nagahisa Yoshimura +7 more
TL;DR: Adapt optics scanning laser ophthalmoscopy (AO-SLO) is a useful means of assessing foveal cone damage objectively and quantitatively and is an important factor determining visual function after MH surgery.
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.