開放隅角緑内障と高眼圧症眼の角膜形状が眼圧測定値に及ぼす影響

Corneal configuration as an interfering factor in intraocular pressure values in primary open angle glaucoma and ocular hypertension

　眼圧測定値が中心角膜厚と角膜曲率でつくられる角膜力学特性にどのように影響されるかを，開放隅角緑内障24眼と高眼圧症89眼で検討した。眼圧は非接触眼圧計で，中心角膜厚は超音波角膜厚測定装置で計測した。中心角膜厚と角膜曲率半径から求めた角膜変形度は，高眼圧症眼で緑内障眼よりも有意に小さかった（p＜0.01）。高眼圧症では角膜弾性が高く，このために眼圧値が過大評価されていると推定された。治療前の眼圧と角膜変形度の症例ごとの検討から，眼圧，中心角膜厚，角膜曲率半径を指標として、視野異常の危険率の高い群（開放隅角緑内障）と低い群（高眼圧症）とに明確に区別でき，その精度は眼圧値による区別よりも高かった。角膜形状は眼圧測定値に影響すること，さらに眼圧と視野との関係にも影響することが結論された。

We studied 24 eyes of primary open angle glaucoma and 89 eyes of ocular hypertension regarding the intraocular pressure (IOP) and corneal configuration which was calculated from the central corneal thickness and corneal curvature. The TOP was measured by a noncontact tonometer. The corneal thickness was measured by an ultrasound corneal pachymeter. Eyes with ocular hypertension showed significantly higher corneal rigidity, or lesser corneal deformity, as calculated from the corneal thickness and curvature (p ＜ 0.01) . This feature appeared to mean that the measured IOP values tend to be overestimated in ocular hypertension. It was possible to assess the future risk of visual field impairment by using pretreatment TOP levels, corneal thickness and curvature as parameters. This assessment was more sensitive than using IOP alone as parameter. The findings also show that the corneal configuration is one of the interfering factors for IOP values and for the relationship between IOP and visual field.