光学的非接触術中眼軸長測定法

Optical noncontact measurement of axial length during cataract surgery

　挿入眼内レンズ屈折力の予測精度を向上させる目的で，光学的手法による非接触術中眼軸長測定法を開発し，眼内レンズ一次挿入例57例に適用した。この方法は，白内障術中に無水晶体眼の屈折度を手持ちオートレフラクトメータとハードコンタクトレンズとを用いて測定し，その値から遠点を求め，光線追跡法で網膜位置を決め，眼軸長を求める方法である。従来の超音波法と同等の精度で測定することが確認でき，患者の固視が困難な例ではより優れた精度が得られた。術前に従来の方法による眼軸長測定が困難な例でも適用でき，挿入眼内レンズ屈折力決定の精度向上に寄与できると考えられた。

In order to improve the accuracy of axial length measurement, we developed a noncontact optical method to be used during cataract surgery. The system consists of a portable infrared autore-fractometer and a contact lens. The refractive power of aphakia was measured just before im-plantation of intraocular lens (IOL) in 57 eyes. The values were converted into axial length using a ray -tracing technique and a computer to determine theoptimum power of IOL to be inserted. The obtained values were well correlated with those by conven-tional ultrasonic method (r=0.982). The difference between the two methods was less than 0.35mm in 54 eyes, 95%, and greater in 3 eyes, 5%. In the latter group, ultrasonic measurements gave lesser values than the present method. The findings show that the optical method gives more accurate values for the axial length, contributing to better results after cataract surgery with IOL implantation.