| 摘要 |
A sensor 17 detects a quantity of light emitted by an alignment light source 21 and reflected by an eye. A comparison circuit 53 compares a quantity of the reflected alignment light with a predetermined quantity of reference light. If the reflected alignment light is less in quantity than the reference light, the comparison circuit 53 judges that there exist stains which exert a bad influence on the reflected alignment light. An operator obtains the judgment through a monitor 52 by which cautions are offered, so that the operator can operate an instrument in the best condition.
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