Rein David B, Wirth Kathleen E, Johnson Chris A, Lee Paul P
RTI International, Atlanta, Georgia 30341, USA.
Ophthalmic Epidemiol. 2007 Jul-Aug;14(4):258-64. doi: 10.1080/01658100701473267.
To develop a function to describe quality-adjusted life year (QALY) losses associated with visual field losses for use in cost-effectiveness models.
We estimated the patient visual field defect in decibels (dBs) that corresponded to visual acuity values of 20/40, 20/70, 20/200 (US blindness), 20/400 (WHO blindness), and 20/1,000 (extreme impairment) using two methods. The first method categorized visual field defects by applying the logic of the Snellen minimum angle of resolution (MAR) acuity scale to the ability to perceive luminance adjusting for the differences in the visual acuity and luminance scales (MAR-based). The second method categorized visual field defects based on assumptions. We then assigned each visual field category the same QALY value associated with the analogous visual acuity category. Finally, for each method, we calculated a function that described QALY losses as a function of the absolute value of patient mean deviation (MD) values measured in dBs.
The MAR-based method estimated that MDs of -16, -18, -23, -24, and -30 or greater dBs corresponded to visual acuity values of 20/40, 20/70, 20/200, 20/400, and 20/1,000, respectively. For the same visual acuity values, the assumption-based method resulted in MD estimates of -13, -17, -22, -24, and -30. Our MAR-based method yielded the function, QALYs = 0.98991 + 0.0022 . dBs -0.00080518 . dBs2, setting dBs equal to the absolute value of the mean deviation in the better-seeing eye. OUR ASSUMPTION-BASED METHOD YIELDED THE PIECE-WISE FUNCTION, QALYS = 1.0 - 0.0155 . DBS FOR DBS < 22, AND 1.815 -0.0525. DBS FOR DBS >OR= 22.
Results from two estimation methods suggest a convex and downward sloping relationship between dBs of visual field loss and QALY decrements. QALY losses accumulate slowly at first and then increase at an accelerating rate following an MD of approximately -10 dBs. This relationship is consistent with recent empirical findings reporting minimal QALY losses associated with small visual field defects.
开发一种函数，用于描述与视野损失相关的质量调整生命年（QALY）损失，以用于成本效益模型。
我们使用两种方法估计了与视力值20/40、20/70、20/200（美国失明标准）、20/400（世界卫生组织失明标准）和20/1000（极度损伤）相对应的以分贝（dB）为单位的患者视野缺损。第一种方法通过将斯内伦最小分辨角（MAR）视力表的逻辑应用于感知亮度的能力来对视野缺损进行分类，同时调整视力和亮度量表之间的差异（基于MAR）。第二种方法基于假设对视野缺损进行分类。然后，我们为每个视野类别赋予与类似视力类别相同的QALY值。最后，对于每种方法，我们计算了一个函数，该函数将QALY损失描述为以dB为单位测量的患者平均偏差（MD）值绝对值的函数。
基于MAR的方法估计，-16、-18、-23、-24和-30dB或更高的MD分别对应于20/40、20/70、20/200、20/400和20/1000的视力值。对于相同的视力值，基于假设的方法得出的MD估计值为-13、-17、-22、-24和-30。我们基于MAR的方法得出的函数为：QALYs = 0.98991 + 0.0022·dBs - 0.00080518·dBs²，其中dBs等于视力较好眼睛的平均偏差绝对值。我们基于假设的方法得出的分段函数为：当dBs < 22时，QALYs = 1.0 - 0.0155·dBs；当dBs≥22时，QALYs = 1.815 - 0.0525·dBs。
两种估计方法的结果表明，视野损失的dB与QALY下降之间存在凸形且向下倾斜的关系。QALY损失起初积累缓慢，然后在MD约为-10dB后加速增加。这种关系与最近的实证研究结果一致，该研究报告称小视野缺损导致的QALY损失最小。
