Naugle Exophthalmometer Spirit Level is an accessory intended to insure that the instrument is level when measuring vertical displacement of the globe. It also Aides in placing the head in the vertical position during measurement. Compared to other exophthalmometers, the Naugle Exophthalmometer equipped with this spirit level option permits measurement of both hyper- and hypo-ophthalmos with the vertical gradient scale.

Use of the Spirit Level is dependent upon careful vertical positioning of the head. Consequently, positioning of the patient with a chin rest may be helpful in vertical positioning of the head and limiting movement of the head. With this accomplished, the Naugle instrument is positioned using the spirit level centering the bubble. Obtain readings on the vertical scale for possible hyperophthalmos and hypo-ophthalmos, the anterior surface of the cornea is measured for anterior and posterior readings on the horizontal gradient scale (while using the red vernier to decrease parallax).