The investigators hypothesize that this modified ophthalmic draping will reduce the accumulation and rebreathing of carbon dioxide during eye surgery.

Majority of eye surgery has been widely done under local anesthesia provided by the ophthalmologist with or without sedation.The surgical drapes used often covers the patients face and beyond in order to maintain sterility of the surgical field. This can lead to accumulation of carbon dioxide under ophthalmic drapes due to the exhaled carbon dioxide escapes incompletely through the drapes;hence results in an increase of carbon dioxide in the ambient air surrounding the patient's head.This causes an increase in arterial carbon dioxide partial pressure and thus hyperventilation and patient discomfort with restlessness and unable to stay still during the surgery.

In recent years,several types of ophthalmic drapes have been produced.This study is look for possible difference in accumulation of carbon dioxide under the standard ophthalmic drapes compared to the modified draping.

Inclusion Criteria:

- ASA physical status I,II OR III,adult aged 40 to 80 years old,scheduled to undergo elective eye surgery under local anaesthetic at UMMC will be enrolled in this study.

Exclusion Criteria:

• Pre-existing pulmonary disease,psychological disorders,neurological disorder and patient required sedation.