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Wadim Bowl, Birgit Lorenz; Fundus-controlled two-color adaptometry with the Microperimeter MP1. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3024.
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To provide fundus-controlled two-color adaptometry of mesopic vision with an existing device without modifying the CE-marked Microperimeter MP1 itself. Rod and cone sensitivity can be measured and differentiated on defined retinal positions the examiner is most interested in.
An external filter holder was imposed on the objective lens of the MP1 (Nidek, Padova, Italy) and fitted with filters to modify background and stimulus intensity. Light output of the MP1 was reduced by Schott RG780 and BG3 filters outside the instrument to create the stimulus colors red and blue, which were used alternating in this examination. Absorption of infrared light by these filters is low thereby minimizing problems with fundus observation by the built-in infrared camera system. After bleaching with a Ganzfeld ColorDome (Espion E2, Diagnosys LLC, Lowell, MA, USA) with a luminous intensity of 3000 cd/m2 for 5 minutes, twenty normal subjects were investigated with a pattern covering 3 spots at the posterior pole of the retina (3 blue spots at 12° nasal; 3 red spots at 0° and 1°). The test was repeated every 3 minutes during the first 15 minutes and every 5 minutes until 45 minutes of dark-adaptation. Thresholds were determined using a 200 ms red Goldmann IV stimulus and a blue Goldmann III stimulus employing the built-in 4-2 strategy in a dark room.
In the first 5 minutes a slight increase of median light increment sensitivity (LIS) was measured for the red stimulus. With further dark-adaptation, LIS to red stimuli remained at about 7 dB. For blue stimuli LIS increased considerably during the first ten minutes. With processing time sensitivity to blue stimuli reached a plateau at 15 dB. Both measurements showed typical characteristics of dark-adaptation-curves.
Two-color fundus-controlled adaptometry with a commercial MP1 without internal changes to the device provides a quick and easy examination of rod and cone function during dark adaptation at defined retinal loci. Under the mesopic lighting conditions chosen, LIS for blue stimuli is determined by the rod pathway. LIS for red stimuli is mediated by the cone pathway. The method should be helpful to identify rod vs. cone function in the posterior pole in early stages of retinal degenerations.
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