7
views
0
recommends
+1 Recommend
0 collections
    0
    shares
      • Record: found
      • Abstract: found
      • Article: not found

      Improvements on Littmann's method of determining the size of retinal features by fundus photography.

      Graefe's Archive for Clinical and Experimental Ophthalmology

      Fundus Oculi, Humans, Mathematics, Ocular Physiological Phenomena, Photography, methods, Retina, anatomy & histology, physiology, Vision, Ocular

      Read this article at

      ScienceOpenPubMed
      Bookmark
          There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

          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.

          Related collections

          Most cited references 2

          • Record: found
          • Abstract: not found
          • Article: not found

          Repeatability reproducibility and intersession variability of the Allergan Humphrey ultrasonic biometer

            Bookmark
            • Record: found
            • Abstract: not found
            • Article: not found

            A method of determining the equivalent powers of the eye and its crystalline lens without resort to phakometry

              Bookmark

              Author and article information

              Journal
              8082844

              Comments

              Comment on this article