Examination of the ten degrees of visual field surrounding fixation

Transcription

1 Examination of the ten degrees of visual field surrounding fixation Michael Wall, M.D. Tulane University School of Medicine NANOS, 1987 Albrecht von Graete :ntroduced visual field testing into clinical ophthalmology in He used a 3 x 4 foot blackboard divided ~nto 3 ~n. squares as his campimeter and a piece of chalk as his test target. (1) Jannik Peterson Bjerrum developed the Bjerrum screen l n 1889.(2) Using a test distance of 2 meters and test objects as s mall as 1 meter, he was able to accurately map the centra~ 10 degrees. With the widespread use of the Goldmann perimeter, f ollow:ng its introduction ~n ly~~' there was ~mproved quantitation of the peripheral fiela. However, in many perimetrists h a~d s, there was a deemphasis of detailed testing of the central 10 degrees un~ess statlc pe r~metry was performed. Mark Amsler began development of a series of charts in the 1920 ' s. They were designed specifically to qualitatively analyze the disturbances of visual function in the central 10 degrees which accompany the beginnlng and evolution of maculopathies. The charts were pub l~sned o y tne Hamblin Co. in 1949 and have since become star.aar~ equ:pment in the general and neuro-ophthalmologists offices. (3-5} Using cross-polarizing filter s to vary perceived

2 luminance, (threshold Amsler grid testing) this test can be made more sensitive for the detection of scotomas and depressions.(6) Following Fankhauser's contributions on automated perimetry in the 1970 's threshold testing of the central 10 degrees is now more easily accomplished with the bowl perimeter. In addition to automated perimetry, we commonly test the central 10 degrees with the Amsler grid, tangent screen and Goldmann perimeter. I. Goldmann perimeter A. fixation monitor-can ' t routinely test central 2 degrees B. adequate threshold testing requires static attachment c. minification effect of short testing distance (30 em) II. Tangent screen examination (2 meter) A. magnification effect B. example strategy- see fig 1 c. use of 1/2 mm red target D. use of suprathreshold static examlnation N.B. beware of the Troxler effect III. Automated perimetry A. coordinate points are thresholded B. points are located at 3 or 6 degree intervals c. time consuming D. what is abnormal? I V. Amsler grid testing A. suprathreshold target B. detects metamorphopsia c. rapidly performed v. Threshold.Amsler grid testing A. threshold target (see fig 2) B. requires low luminance conditions c. poor f or metamo~phcp si a detect ion D. rapidly performed VI. Technique of threshold Amsler grid testing (6-8) A. occlude eye not be1ng tested B. give patient prop e ~ correction for near c. the standard white Amsler grid, (chart #1) white grid on black background is held em from the eye D. with rotation of the front polarizer, the angle of polarization is slowly increased until the patient can barely

3 see the white dot in the center of the grid but not the grid (this is usually between degrees of polarization) E. the angle of polarization is then decreased one degree at a time until the grid can barely be seen (this usually occurs after 1-2 degrees) this angle is recorded for reproduction of testing conditions at a follow-up office visit F. the patient then draws out any defects present N.B. since normal subjects may note that corners of the grid are missing, these defects are ignored VII. Comparison of testing with tangent screen (2M), automated perimetry and Amsler grids (6) A. 10 consecutive patients with optic neuropathies B. number of defects found 1. standard Amsler grid testing threshold Amsler grid testing M tangent screen exam OCTOPUS prog # 61 (6 degrees) OCTOPUS prog # 32 (30 degrees) - 5 c. total area of defects in square min. of arc 1. standard Amsler grid - 97, threshold Amsler grid - 525,000 D. 2 / 3 of the defects found with threshold Amsler testing were confirmed with another type of examination VIII. Threshold Amsler (TA) grid testing in maculopathies A. 10 patients wit h normal standard Amsler (SA ) grid testing B. all had ophthalmoscopic evidence of a macular lesion c. subjects viewed SA, TA, a bright red grid (BR) and the fine red grid (FR) found in the older sets D. number of defects found 1. standard Amsler grid bright red grid fine red grid threshold Amsler grid tan ge~~ screen confrontation v. f. - 3 E. total area of defects in square min. of arc 1. standard Ams l er grid bright red grid fine red grid - 25~ 4. threshold Amsler grid F. metamorphopsia resolved as one progressed ~n the sequence SA to BR to FR to TA. G. wi t r. TA the area that had shown metamorphopsia was often the site of a field defect

4 REFERENCES 1. Von Graefe A, Examination of the visual field in amblyopic disease. Archives Fur Ophthalmologie 1856; 2: Bjerrurn JP, An addition to the general examination of the field of vision Scand 0 Mag 1889; 2: Amsler M, L'examen qualitatif de la f6nction maculaire. Ophthalmologica 1947; 1142: Amsler M, Quantitative and qualitative vision. Trans Ophthal Soc UK 1949; 69: Amsler M, Earliest symptoms of disease of the macula. Br J Ophthalmol 1953; 37: Wall M, Sadun AA, Threshold Amsler grid testing; crosspolarizing lenses enhance yield. Arch 9Phthalmol 1986; 104: Sadun A, Lessell s. Brightness-sense and optic nerve disease. Arch Ophthalmol 1985; 103: Mainster MA, Dieckert JP, A simple haploscopic method for quantitating color brightness comparison. Am J Ophthalmol 1980 ; 89 :

5 JA Figure 1. Sagittal section of visual island as would be plotted by static perimetry. Relative scotoma (diagonal lines) is detected by threshold Amsler grid testing (TA). Standard Amsler grid stimulus surveys the island at too great a depth to detect the scotoma. Figure 2. Example or s~rate gy ior klnetic and static 2 meter tangent screen examinat1on. Arrows represent kinetic targets. Dots represent suprathreshold static stimuli.