目的:通过将双色视野与阈值与强度(tvi)测试相结合,探索色素性视网膜炎视锥敏感性丧失的机制。
方法:招募了7名常染色体隐性遗传性色素性视网膜炎的受试者和10名正常受试者,并使用在暗视条件下呈现的480和640nmGoldman大小V目标对一只眼睛进行了周边测试条件条件(无背景照明)和白色背景下,亮度范围为-1.5至2logcdm-2,范围为0.5logcdm-2。数据用logT=logT0+log((A+A0)/A0)n形式的tvi函数拟合,其中T是阈值,T0是绝对阈值,A是背景强度,A0是暗光常数,n是增益常数。
结果:在光学相干断层扫描中,在与椭圆体区丢失相对应的视野区域内无法获得可靠的tvi函数。在固定时,观察到T0和A0的变化,与d1机制损失一致,这导致了tvi函数的向上和向右移位。在[±3°处损失,±3°]显示T0的变化,与d3机制损失一致,导致tvi曲线向上平移。
结论:尽管每个位置的绝对视锥阈值都升高了,固定时tvi功能的变化(所谓的d1机制损失)在存在白色适应背景的情况下最小化阈值升高,例如通常在标准双色视野中使用的那些。在更多的外围测试地点,阈值的变化与背景亮度无关(所谓的d3机制损失)。这些发现表明,背景选择性地适应杆,同时保持视锥在,或附近,绝对阈值可能比传统的双色视野法更适合评估视锥灵敏度的损失,尤其是在固定点。
OBJECTIVE: To explore the mechanisms of cone sensitivity loss in retinitis pigmentosa by combining two-colour perimetry with threshold versus intensity (tvi) testing.
METHODS: Seven subjects with autosomal recessive retinitis pigmentosa and 10 normal subjects were recruited and underwent perimetric testing of one eye using 480- and 640-nm Goldman size V targets presented under scotopic conditions (no background illumination) and against a white background ranging in luminance from -1.5 to 2 log cd m-2 in 0.5 log cd m-2 steps. Data were fitted with tvi functions of the form logT = logT0 + log ((A + A0)/A0)n, where T is the threshold, T0 is the absolute threshold, A is the background intensity, A0 is the \'dark-light\' constant and n is a gain constant.
RESULTS: Reliable tvi functions could not be obtained within the region of the visual field corresponding to loss of the ellipsoid zone on optical coherence tomography. At fixation, changes in both T0 and A0 were observed, consistent with a d1 mechanism loss, which resulted in an upwards and rightwards shift of the tvi function. Losses at [±3°, ±3°] demonstrated changes in T0, consistent with a d3 mechanism loss, resulting in an upwards translation of the tvi curve.
CONCLUSIONS: Although the absolute cone threshold was elevated at each location, shifts in the tvi function (so-called d1 mechanism loss) at fixation minimise threshold elevation in the presence of white adapting backgrounds, such as those typically employed in standard two-colour perimetry. At more peripheral testing locations, changes in threshold occurred independent of background luminance (so-called d3 mechanism loss). These findings suggest that backgrounds which selectively adapt rods while maintaining cones at, or near, absolute threshold may be preferable to conventional two-colour perimetry for assessing loss of cone sensitivity, especially at the point of fixation.