Imaging and Perimetry Society

About IPS
Joining IPS
Membership List
Site Map

Short Wavelength Automated Perimetry  (SWAP)

Chris A. Johnson Ph.D.


Printer-Friendly pdf version

The pioneering work of Stiles provided a means of psychophysically isolating and measuring the sensitivity of individual color vision mechanisms through the two-color increment threshold procedure.1,2  Basically, this approach involved decreasing the sensitivity of some color vision mechanisms (termed π mechanisms by Stiles) by using a chromatic adapting background light, and then measuring the sensitivity of another color vision mechanism by means of a narrow band chromatic stimulus.  According to Stiles’ terminology, π0 refers to the sensitivity of the rod system, π1, 2 and 3 are short wavelength (“blue”) sensitive mechanisms, π4 is a middle wavelength (“green”) sensitive mechanism, and π5 is a long wavelength (“red”) sensitive mechanism.  Isolation of π1, the principal short wavelength (“blue”) sensitive mechanism, was best achieved with a high luminance (greater than 50 cd/m2) white or broad spectrum yellow background (530 nm short wavelength “cutoff” filter), and a large (greater than 2 degrees in diameter) narrow band (440 nm peak wavelength with a 10-20 nm bandwidth) short wavelength stimulus.  The figure below and to the right shows the spectral sensitivity of three color vision mechanisms (π1, π4, and π5) under normal viewing conditions on the left graph.  ""The vertical blue line indicates the peak of the short wavelength mechanism and the vertical yellow line indicates the peak wavelength of the background.  The graph is plotted in a threshold versus wavelength format, in which the background chromaticity and luminance are constant, the stimulus wavelength is varied and the stimulus increment threshold is determined.  Note that under these conditions, sensitivity to a short wavelength stimulus is higher for the middle and long wavelength systems than for the short wavelength system.  The graph to the right shows the same spectral sensitivity profile in the presence of a bright broadband yellow background.  Here one can observe that there is substantially decreased sensitivity for the middle and long wavelength mechanisms, thereby permitting the short wavelength mechanism’s sensitivity to be isolated and measured.


Several investigators were able to adapt this technique for use in testing patients with various ocular and neurologic disorders.3,4  Most of this initial work concentrated on the evaluation of the fovea and possibly a limited number of extra foveal locations.  An example of the results obtained from these early studies is shown on the top graph presented to the right.  This data representation format is a threshold versus intensity (or threshold versus radiance) type of representation in which the chromaticity of the stimulus and background are held constant, the luminance of the background is varied on successive trials, and the stimulus increment threshold is determined.  As shown by the left portion of the graph (labelled π4), the increment threshold sensitivity is unaffected by the luminance of the background, thereby demonstrating a horizontal line.  At some point, the background begins to exert an effect, and more light must be added to the stimulus to make it detectable, and this relationship between stimulus and background luminance is linear.  When the background luminance becomes higher, it may significantly adapt one mechanism (in this instance, π4) and another, more sensitive, mechanism may then detect the stimulus, as indicated in the figure where π1 becomes prominent. Thus, the departures from linearity in the graph are indications that stimulus detection is being transferred from one mechanism to another, more sensitive mechanism. A similar threshold versus intensity curve is presented in the middle graph for an extrafoveal location.4

More recently, several laboratories have attempted to adapt this procedure for automated perimetric testing.5-12 In particular, a procedure that isolates and measures the short wavelength sensitive mechanisms has been of interest, and it has come to be referred to as Short Wavelength Automated Perimetry (SWAP). 


The lower graph on this page presents threshold versus sensitivity curves for an eccentric location that was obtained using the two-color increment threshold technique on a modified automated perimeter.  Initially, it was also determined that there were normal aging effects that were greater than for standard automated perimetry,5,10 and that these aging effects were partly due to optical factors12 and some were due to neural losses.6 Subsequent investigations found that normal aging effects were essentially equivalent for all visual field procedures if the dynamic ranges are taken into account.13  It has also been reported that there are learning effects that occur for SWAP.14,15  Specific details about the SWAP procedure are beyond the scope of this presentation, and the interested reader is encouraged to review the literature citations included with this presentation.1-63  The initial methods for performing SWAP were slightly different among the various laboratories, but after its clinical effectiveness had been established, many of the laboratories were able to collaborate and define optimal clinical test conditions for SWAP, which was extremely beneficial for its application in the eye clinic.16 

It was determined that a broadband yellow filter (OG530 Schott filter – a 530 nm short wavelength cutoff filter) for the background, a background luminance of 100 cd/m, 2 a large stimulus (Goldmann Size V, about 1.7 degrees diameter) with a narrow band short wavelength interference filter (440 nm peak transmission, with a 15 nm bandwidth) and a 200 millisecond stimulus duration was the most appropriate set of conditions for performing SWAP testing.  The table to the right indicates that under these conditions, the bottom filter condition (5b) shows that one was able to obtain 1.4 to 1.7 long units of isolation of the short wavelength sensitive mechanisms (14 to 17 dB), which subsequent studies have shown makes it possible to maintain isolation of these mechanisms throughout the entire operating range of the visual field instrument and for all levels of visual field damage.17-19  In this Table, DNT refers to “did not test”. The figure to the right presents a view of the SWAP procedure as performed by an automated perimeter that was modified to conduct this test procedure. Our best current understanding of the mechanisms underlying SWAP detection is that it is mediated by input from the cone photoreceptors through inner retinal interactions and subsequent processing by a group of retinal ganglion cells that are responsible for coding blue-yellow opponent color processing.64,65  These ganglion cells comprise approximately 5% of the total number of ganglion cells and are believed to project to the intralaminar cells (Koniocellular cells) in the lateral geniculate nucleus.64,65  In this view the neural mechanisms underlying SWAP are sparse and are uniquely designed to be specifically responsive to this type of stimulus display.

As with all diagnostic test procedures, SWAP has some advantages and disadvantages. Longitudinal investigations performed at several different laboratories have demonstrated that SWAP is able to identify glaucomatous visual field deficits earlier than standard (white-on-white) automated perimetry,8,20-34 revealing deficits in approximately 20-25% of patients at risk of developing glaucoma who have repeatedly normal visual field results for standard automated perimetry.  The pattern of visual field loss corresponds to those that would be expected to occur as a consequence of retinal nerve fiber bundle deficits in glaucoma.7,35  Additionally, the size of SWAP defects are usually larger than those observed for standard automated perimetry,7,9,36-38 and progression of SWAP deficits is typically greater than for standard automated perimetry.7,9,36-38 Additional studies have demonstrated that SWAP deficits can be confirmed by subsequent testing more frequently than standard automated perimetry losses,24 and that isolation of short wavelength sensitive mechanisms can be maintained throughout the entire dynamic range for SWAP testing, even in damaged visual field areas.17-19  Perhaps the greatest advantage of SWAP is that it is able to predict the onset and location of future glaucomatous visual field deficits for standard automated perimetry by 3-5 and possibly 10 years.20-34  Two examples of this predictive value of SWAP are presented below, where SWAP results for five consecutive years are presented in the bottom panels and standard automated perimetry results are presented in the top panels.  Locations that are within the 95% normal confidence limits (adjusted for age) are indicated by gray circles, whereas locations that are worse than the lower normal 5% limit are indicated by yellow circles, and locations that are worse than the lower 1% level are denoted by red circles.




"" SWAP has several disadvantages as well. First, it is more variable than standard automated perimetry,39 is affected by the absorption properties of the crystalline lens,12 and is more difficult for some patients to perform.  However, these disadvantages do not deter from the clinical value of SWAP, and methods have been developed to account for these disadvantages.  This has enhanced the robustness and viability of SWAP as a routine clinical diagnostic test procedure. Recently, several laboratories have examined the relationship between SWAP deficits and structural deficits produced by glaucoma, thereby enhancing our knowledge of the basis for glaucoma pathophysiology. 40-43

SWAP has also been useful for diagnostic evaluation of ocular and neurologic diseases other than glaucoma.  SWAP has been found to be useful in the visual field evaluation of patients with diabetic retinopathy and other retinal diseases,44-53 optic neuropathies, pre-chiasmal, chiasmal and post chiasmal deficits,54-56 migraine,57,58 and other disorders.  In most instances, the deficit noted for SWAP is more extensive than those observed for standard automated perimetry, or the deficit is present for SWAP but is not evident on standard automated perimetry.  The figure to the right56 demonstrates an example of standard automated perimetry (top graphs) and SWAP (bottom graphs) for both eyes of a patient with normal test results (repeatedly) for standard automated perimetry and a right homonymous hemianopic visual field deficit for SWAP (repeatedly).  Several neuro-ophthalmology exams revealed no remarkable findings that could account for the hemianopic visual field deficit for SWAP.  However, an MRI scan revealed multiple disseminated plaques that were present in both hemispheres, but were particularly prominent in the left hemisphere that would correspond to the right SWAP homonymous hemianopsia.

""One of the shortcomings associated with the commercial version of SWAP is the length of time required to perform testing.  Typically, SWAP testing required 2-3 minutes longer that the Full Threshold procedure for standard automated perimetry, creating test times of 15-20 minutes per eye.  Recently, several laboratories have applied Bayesian test strategies to the SWAP procedure in order to provide a more efficient method of testing for clinical diagnostic purposes.59-62  SITA SWAP has been reported to provide sensitivity for detection of glaucomatous visual field loss that is highly similar to the Full Threshold SWAP approach.  Also, the variability of SITA SWAP, both within and between subjects, was found to be equal to or less than that observed for the standard SWAP procedure.59-62  Additionally, the SITA SWAP procedure has been reported by two independent laboratories to have 4-5 dB of increased sensitivity for each test location, when compared to the standard SWAP procedure.59-62  This has the advantage of increasing the dynamic range of SWAP, which makes it possible to monitor damaged visual field areas in a better manner, which is a distinct benefit in view of SWAP’s more limited response operating range when compared to standard automated perimetry.  Some of the factors responsible for this increased dynamic range for SITA SWAP have been identified, while other remain to be determined.63  The figure to the right shows an example of SITA SWAP for the right eye of a patient with glaucomatous visual field loss. A superior partial arcuate deficit is detected within a test duration interval of approximately 4 minutes and 9 seconds.

SWAP is currently implemented on several commercially available automated perimeters (along with a normative database and statistical analysis package), include the Humphrey Field Analyzer II (Model 700 and higher) and Octopus perimeters.  In view of the available literature devoted to SWAP, it would also be a rather straightforward procedure for many other manufacturers to provide SWAP as a test procedure as well.

In summary, SWAP has been a technique that has taken many years to develop and refine, has had several laboratories conducting longitudinal evaluations of its clinical capabilities, and continues to be refined.  It therefore serves as a good example of the type of work necessary to validate a clinical diagnostic test procedure.



  1. Stiles WS, Color vision: the approach through increment threshold sensitivity.   Proc Nat Acad Sci, 1959, 45: 100-114.

  2. Enoch JM,   The two color threshold technique of Stiles and derived component color mechanisms. In Handbook of Sensory Physiology VII/4 - Visual Psychophysics (Jameson and Hurvich, eds), Chapter 21, Berlin: Springer-Varlag, 537-567.

  3. Kranda K, King-Smith PE, What can colour thresholds tell us about the nature of the underlying detection mechanisms? Ophthalmic Physiol Opt, 1984, 4: 83-87.

  4. Kitahara K, Tamaki R, Noji J, Kandatsu A, Matsuzaki H,  Extrafoveal Stiles p m mechanisms.  Doc Ophthalmol Proc Series: Fifth International Visual Field Symposium, 1983, The Hague: Junk Pub, 397-403.

  5. Johnson CA, Adams AJ, Twelker JD, Quigg JM:  Age-related changes in the central visual field for short-wavelength-sensitive pathways.  Journal of the Optical Society of America A, 1988, 5: 2131-2139.

  6. Johnson CA, Adams AJ, Lewis RA:  Evidence for a neural basis of age-related visual field loss in normal observers.  Investigative Ophthalmology and Visual Science, 1989, 30: 2056-2064.

  7. Adams AJ, Johnson CA, Lewis RA:  S cone pathway sensitivity loss in ocular hypertension and early glaucoma has nerve fiber bundle pattern.  Proceedings of the 10th Symposium of the International Research Group on Colour Vision Deficiencies, (Drum, Moreland and Serra, eds.), The Netherlands: Kluwer Academic Publishers, 1991, pp. 535-542.

  8. Johnson, CA, Adams, AJ, Casson, EJ, Brandt, JD :  Blue-on-Yellow perimetry can predict the development of glaucomatous visual field loss.  Archives of Ophthalmology, 1993, 111: 645-650.

  9. Johnson, CA, Adams AJ, Casson EJ, Brandt JD :  Progression of early glaucomatous visual field loss for Blue-on-Yellow and standard White-on-White automated perimetry.  Archives of Ophthalmology, 1993, 111: 651-656.

  10. Sample PA, Weinreb RN, Boynton RM: Acquired dyschromatposia in glaucoma.  Survey of Ophthalmology, 1986, 81: 54-64.

  11. Sample PA, Weinreb RN: Progressive visual field loss in glaucoma. Investigative Ophthalmology and Vision Science, 1992, 33: 2068-2071.

  12. Sample PA, Martinez GA, Weinreb RN: Short wavelength autopated perimetry without lens density testing.  AM J Ophthalmol, 1994, 118: 632-641.

  13. Gardiner SK, Johnson CA, Spry PGD:  Normal age-related sensitivity loss for a variety of visual functions throughout the visual field. Optom Vis Science, 2006, 83: 438-443.

  14. Rossetti L, Fogagnolo P, Miglior S, Centofanti M. Vertrugno M, Orzalesi N: Learning effect of short-wavelength automated perimetry in patients with ocular hypertension. J Glaucoma, 2006, 15: 399-404.

  15. Wild JM, Kim LS, Pacey IE, Cunliffe IA:  Evidence for a learning effect in short wavelength automated perimetry.  Ophthalmology, 2006, 113: 206-215.

  16. Sample PA, Johnson CA, Haegerstrom-Portnoy G and Adams AJ,  Optimum parameters for short-wavelength automated perimetry.  J Glaucoma, 1996, 5: 375-383.

  17. Felius J and Swanson WH,  Effects of cone adaptation on variability in S-cone increment thresholds.  Invest Ophthalmol Vis Sci, 2003, 44: 4140-4146.

  18. Demirel S and Johnson CA,   The influences of stimulus wavelength and eccentricity on short wavelength pathway isolation in automated perimetry.  Ophthalmic Physiol Opt, 2001, 21: 1-8.

  19. Demirel S and Johnson CA,  Isolation of short-wavelength sensitive mechanisms in normal and glaucomatous visual field regions.  J Glaucoma, 2000, 9: 63-73.

  20. Sit AJ, Medieros FA and Weibren RN,  Short-wavelength automated perimetry can predict glaucomatous standard visual field loss by ten years.  Semin Ophthalmol, 2004, 19: 122-124.

  21. Mansberger SL, Sample PA, Zangwill LM and Weinreb RN,   Achromatic and short-wavelength automated perimetry in patients with glaucomatous large cups.  Arch Ophthalmol, 1999, 117: 1473-1477.

  22. Johnson CA,  The diagnostic value of Short Wavelength Automated Perimetry (SWAP).  Current Opinion in Ophthalmology, 1996, 7: 54-58.

  23. Demirel, S. and C.A. Johnson, Short wavelength automated perimetry (SWAP) in ophthalmic practice. J Am Optom Assoc, 1996. 67:451-456.

  24. Demirel, S. and C.A. Johnson, Incidence and prevalence of short wavelength automated perimetry deficits in ocular hypertensive patients. Am J Ophthalmol, 2001. 131: p. 709-715.

  25. Johnson CA, Brandt JD, Khong AM and Adams AJ,  Short wavelength automated perimetry (SWAP) in low, medium and high risk ocular hypertensives: Initial baseline findings.  Archives of Ophthalmology, 1995, 113: 70-76.

  26. Casson EJ, Johnson CA and Shapiro LR,  A longitudinal comparison of Temporal Modulation Perimetry to White-on-White and Blue-on-Yellow Perimetry in ocular hypertension and early glaucoma.  Journal of the Optical Society of America, 1993, 10: 1792-1806.

  27. Sample PA and Weinreb RN,  Color perimetry for assessment of primary open angle glaucoma.  Invest Ophthalmol Vis Sci, 1990, 31: 1869-1875.

  28. Landers, J., I. Goldberg, and S. Graham, A comparison of short wavelength automated perimetry with frequency doubling perimetry for the early detection of visual field loss in ocular hypertension. Clin Experiment Ophthalmol, 2000. 28:  248-252.

  29. Johnson, C.A., Recent developments in automated perimetry in glaucoma diagnosis and management. Curr Opin Ophthalmol, 2002. 13(2): p. 77-84.

  30. Sample PA, Medieros FA, Racette L, Pascual J, Boden C, Zangwill LM, Bowd C and Weinreb RN,  Identifying glaucomatous vision loss with visiual function-specific perimetry in the diagnostic innovations in glaucoma study.  Invest Ophthalmol Vis Sci, 2006, 47: 3381-3389.

  31. Demirel S and Johnson CA,  Short Wavelength Automated Perimetry (SWAP) in ophthalmic practice. Journal of the American Optometric Association, 1996, 67: 451-456.

  32. Lewis RA, Johnson CA and Adams AJ,  Automated static visual field testing and perimetry of short-wavelength-sensitive (SWS) mechanisms in patients with asymmetric intraocular pressures. Graefe's Arch Clin Exp Ophthalmology, 1993, 231: 274-278.

  33. Wild JM,  Short wavelength automated perimetry.  Acta Ophthalmol Scand, 2001, 79: 546-559.

  34. Racette L and Sample PA,  Short wavelength automated perimetry.  Ophthalmol Clin North Am, 2003, 16: 227-236.

  35. Landers J, Sharma A, Goldberg I and Graham S,  Topography of the frequency doubling perimetry visual field compared with that of short wavelength and achromatic automated perimetry visual fields.  Br J Ophthalmol, 2006, 90: 70-74.

  36. Landers JA, Goldberg I, and Graham SL, Detection of early visual field loss in glaucoma using frequency-doubling perimetry and short-wavelength automated perimetry.  Arch Ophthalmol, 2003, 121- 1705-1710.

  37. Bayer, A.U. and C. Erb, Short wavelength automated perimetry, frequency doubling technology perimetry, and pattern electroretinography for prediction of progressive glaucomatous standard visual field defects. Ophthalmology, 2002. 109(5): p. 1009-17.

  38. Soliman, M.A., et al., Standard achromatic perimetry, short wavelength automated perimetry, and frequency doubling technology for detection of glaucoma damage. Ophthalmology, 2002. 109(3): p. 444-54.

  39. Kwon YH, Park HU, Jap A, Ugurlu S, Caprioli J,  Test-retest variability of blue-on-yellow perimetry is greater than white-on-white perimetry in normal subjects.  Am J Ophthalmol, 1998, 126: 29-36.

  40. Johnson, C.A., et al., Structure and function evaluation (SAFE): I. criteria for glaucomatous visual field loss using standard automated perimetry (SAP) and short wavelength automated perimetry (SWAP). Am J Ophthalmol, 2002. 134(2): p. 177-85.

  41. Johnson CA, Sample PA, Zangwill LM, Vasile CG, Cioffi GA, Liebmnn JR and Weinreb RN,   Structure and function evaluation (SAFE) II.  Comparison of optic disc and visual field characteristics.  Am J Ophthalmol, 2003, 135, 148-154.

  42. Shah NN, Bowd C, Medieros FA, Weinreb RN and Sample PA, Combining structural and functional testing for detection of glaucoma.  Ophthalmology, 2006, 113: 1593-1602.

  43. Sanchez-Galeana CA, Bowd C, Zangwill LM, Sample PA and Weinreb, RN,  Short-wavelength automated perimetry results are correlated with optical coherence tomography retinal nerve fiber layer thickness measurements in glaucomatous eyes.  Ophthalmology, 2004, 111: 1866-1872.

  44. Gilmore ED, Hudson C, Nrusimhadevara RK and Harvey PT,  Frequency of seeing characteristics of the short wavelength sensitive visual pathway in clinically normal subjects and diabetic patients with focal sensitivity loss.  Br J Ophthalmol, 2005, 89: 1462-1467.

  45. Razeghinejad MR, Torkaman F and Amini H,  Blue-yellow perimetry can be an early detector of hydroxychloroquine and chloroquine retinopathy.  Med Hypotheses, 2005, 65: 629-630.

  46. Jacobson SG, Marmor MF, Kemp CM and Knighton RW,  SWS (blue) cone hypersensitivity in a newly identified retinal degeneration.  Invest Ophthalmol Vis Sci, 1990, 31: 827-838.

  47. Sakai T, Iida K, Tanaka Y, Kohzaki K and Kitahara K,  Evaluation of S-cone sensitivity in reattached macula following macula-off retinal detachment surgery.  Jpn J Ophthalmol, 2005, 49: 301-305.

  48. Han Y, Adams AJ, Bearse MA, Schneck ME,  Multifocal electroretinogram and short-wavelength automated perimetry measures in diabetic eyes with little or no retinopathy.  Arch Ophthalmol, 2004, 122: 1809-1815.

  49. Afrashi F, Erakgun T, Kose S, Ardic K and Mentes J,  Blue-on-yellow perimetry versus achromatic perimetry in type I diabetes patients without retinopathy.  Diabetes Res Clin Pract, 2003, 61: 7-11.

  50. Remky A, Weber A, Hendricks S, Lichtenberg K and Arend O,  Shot-wavelength automated perimetry in patients with diabetes mellitus without macular edema.  Graefes Arch Clin Exp Ophthalmol, 2003, 241: 468-471.

  51. Remky A, Lichtenberg K, Elsner AE and Arend O,  Short-wavelength automated perimetry in age-related maculopathy.  Br J Ophthalmol, 2001, 85: 1432-1436.

  52. Remky A, Arend O and Hendricks S,  Short-wavelength automated perimetry and capillary density in early diabetic maculopathy.  Invest Ophthalmol Vis Sci, 2000, 41: 274-281.

  53. Hudson C, Flanagan JG, Turner GS, Chen HC, Young LB and McLeod D,  Short-wavelength sensitive visual field loss in patients with clinically significant diabetic macular oedemaI.  Diabetologia, 1998, 41: 918-928.

  54. Walters JW, Gaume A and Pate L,  Short wavelength automated perimetry compared with standard achromatic perimetry in autosomal dominant optic atrophy.  Br J Ophthalmol, 2006, 90: 1267-1270.

  55. Corallo G, Cicinelli S, Papadia, M, Bandini F, Uccelli A and Calabria G,  Conventional perimetry, short-wavelength automated perimetry, frequency-doubling technology and visual evoked potentials in the assessment of patients with multiple sclerosis.  Eur J Ophthalmol, 2005, 15: 730-738.

  56. Keltner JL and Johnson CA,  Short Wavelength Automated Perimetry (SWAP) in neuro-ophthalmologic disorders.  Archives of Ophthalmology, 1995, 113: 475-481.

  57. Yenice O, Temel A, Incili B and Tuncer N,  Short wavelength automated perimetry in patients with migraine.  Grafes Arch Clin Exp Ophthalmol, 2006, 244: 589-595.

  58. McKendrick AM, Cioffi GA and Johnson CA,  Short-wavelength sensitivity deficits in patients with migraine.  Arch Ophthalmol, 2002, 120: 154-161.

  59. Turpin, A., C.A. Johnson, and P.G.D. Spry, Development of a maximum likelihood procedure for Short Wavelength Automated Perimetry (SWAP). Perimetry Update 2000/2002, ed. M.a.W. Wall, J.M. in press, The Hague: Kugler.

  60. Bengtsson B,  A new rapid threshold algorithm for short-wavelength automated perimetry.  Invest Ophthalmol Vis Sci, 2003, 44: 455-461.

  61. Bengtsson B and Heijl A, Normal intersubject threshold variability and normal limits of the SITA SWAP and full threshold SWAP perimetric programs.  Invest Ophthalmol Vis Sci, 2003, 44: 5029-5034.

  62. Bengtsson B and Heijl A,  Diagnostic sensitivity of fast blue-yellow and standard automated perimetry in early glaucoma: a comparison between different test programs.  Ophthalmology, 2006, 113: 1092-1097.

  63. Gardiner SK, Demirel S, Fortune B, Johnson CA and Turpin A,  Why are SITA-SWAP sensitivities higher than those from full threshold SWAP ?  Presented at the XVIIth International Perimetric Society Meeting (Portland, Oregon, July 11-14, 2006.

  64. DaceyDM and Packer OS, Colour coding in the primate retina: diverse cell types and cone-specific circuitry.  Curr Opin Neurobiol, 2003, 13: 421-427.

  65. Dacey DM and Lee BB,  The “blue-on” opponent pathway in primate retina originates from a distinct bistratified ganglion cell type.  Nature, 1994, 367: 731-735.



search this site

Copyright 2008. Imaging and Perimetry Society