Cone density and psychophysical thresholds were investigated in patients with retinitis pigmentosa. Our aim was to assess possible disturbances of foveal cones, especially in patients with good visual acuity. Using the continuously recording densitometer described by van Norren and van der Kraats, we examined ten patients (19 eyes). With the same apparatus it was possible to determine cone final threshold. In all patients double density values were lower than in an age-matched and sex-matched control group of an equal number, and the half time of regeneration was increased in eight eyes. In 12 eyes of eight patients the foveal final threshold was raised above normal. Pseudoprotanomaly was found in seven eyes in four males. Possible explanations for these findings are discussed. Since reduced double density was found in all patients with retinitis pigmentosa, we conclude that disturbed foveal cones are probably a common and rather early feature in this disease. Invest Ophthalmol Vis Sci 24: [1123][1124][1125][1126][1127][1128][1129][1130] 1983 Retinitis pigmentosa is a progressive form of tapetoretinal dystrophy. Typical observations in the disease are the characteristic fundus picture of bone-spicule pigmentation, a lowered or undetectable scotopic b-wave on electrophysiologic examination, an annular scotoma on perimetric examination, and a raised final threshold on examination with the Goldmann-Weekers adaptometer. The disease affects primarily the receptor layer, particularly the cells of the midperipheral retina; in a later stage the cones in the fovea may also become involved. It is well known that the central field of vision may be retained for a long time and that the visual acuity can remain relativily unimpaired, even in the far advanced stages of the disease. When the technique of retinal densitometry came into use, it was to be expected that attention would be especially focused on measuring the properties of the rods, and several investigators demonstrated that a reduction in the density of rhodopsin correlated well with the loss of visual sensitivity. 1 -2 Perlman and Auerbach 3 distinguished two groups of patients: one group with a recessive inheritance, in which the relation between the log threshold elevation and the fraction of rhodopsin was probably linear, and another group with principally dominant inheritance in which absolute threshold elevation was linearly related to the fraction of rhodopsin present. It was our aim to investigate more thoroughly whether densitometric examination could demonstrate an impaired function in foveal cones in patients with retinitis pigmentosa. For this purpose we used the retinal densitometer described by van Norren and van der Kraats, 4 an instrument that enables reliable and relatively easy measurements in patients. To assess the functional state of the fovea, we measured psychophysical cone dark adaptation to all patients with the same apparatus. Our findings show that in all patients tested by densitometry, the double density values were significantly less than normal, and that in several of these subjects the half-time of pigment regeneration was slower than in the normal. Materials and Methods Subjects For the patient group only those patients were selected who had a confirmed retinitis pigmentosa, established by the following criteria. Except for patients 1 and 2, all patients had a family history of retinitis pigmentosa. Patient 5 is a sister of patient 6, patient 4 and 8 are brothers, and patient 9 and 10 are brother
