Skip to main content
Log in

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

  • Laboratory Investigations
  • Published:
Graefe's Archive for Clinical and Experimental Ophthalmology Aims and scope Submit manuscript

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.

This is a preview of subscription content, log in via an institution to check access.

Access this article

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Institutional subscriptions

Similar content being viewed by others

References

  1. Bennett AG (1988) A method of determining the equivalent powers of the eye and its crystalline lens without resort to phakometry. Ophthalmic Physiol Opt 8:53–59

    Google Scholar 

  2. Bennett AG, Rabbetts RB (1990) Clinical visual optics, 2nd edn. Butterworth-Heinemann, Oxford

    Google Scholar 

  3. Littmann H (1982) Zur Bestimmung der wahren Größe eines Objekts auf dem Hintergrund des lebenden Auges. Klin Mbl Augenheilk 180:286–289

    Google Scholar 

  4. Littmann H (1988) Zur Bestimmung der wahren Größe eines Objekts auf dem Hintergrund eines lebenden Auges. Klin Mbl Augenheilk 192:66–67

    Google Scholar 

  5. Rudnicka AR, Steele CF, Crabb DP, Edgar DF (1992) Repeatability, reproducibility and intersession variability of the Allergan Humphrey ultrasonic biometer. Acta Ophthalmol 70:327–334

    Google Scholar 

  6. Sorsby A, Benjamin B, Davey JB, Sheridan M, Tanner JM (1957) Emmetropia and its aberrations. Special report series of the Medical Research Council, no. 293. HMSO, London

    Google Scholar 

Download references

Author information

Authors and Affiliations

Authors

Rights and permissions

Reprints and permissions

About this article

Cite this article

Bennett, A.G., Rudnicka, A.R. & Edgar, D.F. Improvements on Littmann's method of determining the size of retinal features by fundus photography. Graefe's Arch Clin Exp Ophthalmol 232, 361–367 (1994). https://doi.org/10.1007/BF00175988

Download citation

  • Received:

  • Revised:

  • Accepted:

  • Issue Date:

  • DOI: https://doi.org/10.1007/BF00175988

Keywords

Navigation