Kastl P R
Department of Ophthalmology, Tulane Medical School, New Orleans, LA 70112.
Cornea. 1990;9 Suppl 1:S20-2; discussion S23-4. doi: 10.1097/00003226-199010001-00009.
There are several circumstances in which contact lenses (CLs) provide vision inferior to that possible with spectacles. Over time, both soft and rigid gas-permeable (RGP) lenses accumulate deposits that can cloud vision. RGP lenses are especially prone to scratching; some varieties may even become crazed, giving a spiderweb quality to vision. Certain uncommon corneal complications associated with lens wear--infection, neovascularization, ulcers, and severe epithelial edema--may also impair vision, sometimes permanently. CLs often provide less than optimal vision for patients with presbyopia or severe astigmatism. Difficulties with axis stabilization arise with both soft and rigid toric lenses, and these can take several attempts to resolve. Monovision fitting currently offers the best option for presbyopes, but it has an effect on stereopsis, compromising depth perception. Furthermore, patients often require considerable time before adapting to monovision lens use. Finally, even under normal circumstances, certain inherent features of CLs can diminish visual acuity. The water in soft lenses diffuses light; the loss of visual crispness is particularly notable with high-water-content lenses. On the other hand, the small diameter of RGP lenses often contributes to ghosting--a phenomenon in which the edge of the lenses is visible whenever the pupils are widely dilated.
在某些情况下，隐形眼镜（CLs）提供的视力不如眼镜。随着时间的推移，软性和硬性透气性（RGP）隐形眼镜都会积累沉积物，从而模糊视力。RGP镜片特别容易刮花；有些种类甚至可能出现裂纹，使视力呈现出蜘蛛网般的效果。与佩戴镜片相关的某些罕见角膜并发症——感染、新生血管形成、溃疡和严重上皮水肿——也可能损害视力，有时是永久性的。对于老花眼或严重散光患者，隐形眼镜通常无法提供最佳视力。软性和硬性散光镜片都存在轴位稳定困难的问题，可能需要多次尝试才能解决。目前，单眼视力矫正为老花眼患者提供了最佳选择，但它会对视立体觉产生影响，损害深度感知。此外，患者通常需要相当长的时间才能适应单眼视力镜片的使用。最后，即使在正常情况下，隐形眼镜的某些固有特性也会降低视力。软性镜片中的水分会散射光线；高含水量镜片的视觉清晰度损失尤为明显。另一方面，RGP镜片的小直径常常导致重影——一种在瞳孔充分散大时镜片边缘可见的现象。
