Bergmanson Jan Pg, Martinez Jesus G
Texas Eye Research and Technology Center, University of Houston College of Optometry, Houston, Texas, USA.
Clin Exp Optom. 2017 Sep;100(5):522-528. doi: 10.1111/cxo.12583. Epub 2017 Sep 3.
This review surveys available literature for corneal and limbal dimensions. With modern scleral lenses, these measures have become central to determining the overall size of a lens for satisfactory fitting. In general, published values are not based on a definition of what is being measured. In addition, the most widely accepted average corneal diameter measurement, 11.7 × 10.6 mm, emanates from one source published more than 50 years ago. This value was not based on a measurement but appears to be the cumulative impression of measurements from seven studies conducted between 67 and 127 years ago. Furthermore, in most instances, if at all stated, quoted measures are based on horizontal visible iris diameter, providing limited acknowledgement of limbal width and its inclusion as part of the corneal diameter. The corneo-scleral sulcus from one side to the other has been measured, giving a larger diameter, but may include at least part of the limbus. More objective measurements are possible with modern ophthalmic instrumentation but the lack of structural definition and low magnification resolution with these techniques raises concerns with the accuracy of the results. Measurement of the horizontal visible iris diameter does not include the limbal width, which means that the horizontal visible iris diameter is an underestimate of the true corneo-limbal diameter. This review concludes that the width of the limbus has been neither structurally defined nor accurately measured and that there is a need for the development of new protocols for determining the dimensions of the average cornea and limbus. It is predicted that more accurate measures will indicate that to vault across cornea with limbus and provide excellent comfort, the average cornea will need a lens to have a diameter of 16.0 mm or larger.
本综述调查了有关角膜和角膜缘尺寸的现有文献。对于现代巩膜镜而言，这些测量对于确定合适镜片的整体尺寸至关重要。一般来说，已发表的值并非基于对所测量内容的明确定义。此外，最广泛接受的平均角膜直径测量值11.7×10.6毫米来自50多年前发表的一个来源。该值并非基于测量，而是似乎是67至127年前进行的七项研究测量结果的累积印象。此外，在大多数情况下，即使有所说明，引用的测量值也是基于水平可见虹膜直径，对角膜缘宽度及其作为角膜直径一部分的纳入情况提及有限。已经测量了从一侧到另一侧的角巩膜沟，得出的直径更大，但可能至少包括部分角膜缘。使用现代眼科仪器可以进行更客观的测量，但这些技术缺乏结构定义和低放大倍率分辨率，引发了对结果准确性的担忧。水平可见虹膜直径的测量不包括角膜缘宽度，这意味着水平可见虹膜直径低估了真正的角巩膜直径。本综述得出结论，角膜缘的宽度既未在结构上进行定义，也未得到准确测量，需要制定新的方案来确定平均角膜和角膜缘的尺寸。预计更准确的测量将表明，为了跨越角膜和角膜缘并提供极佳的舒适度，平均角膜需要直径为16.0毫米或更大的镜片。
