[The combination of positive cylinders with negative cylinders in the detection of mixed astigmatism].
OBJECTIVE
To study clinical retinoscopy combined positive cylinders with negative cylinders in the detection of mixed astigmatisms.


METHODS
189 cases (340 eyes) with mixed astigmatism were divided into three groups (< 3.00 D; 3.00 approximately 6.00 D; > 6.00 D). There are 156 eyes with mixed astigmatism less than 3.00 D (76 eyes in experiment group, 80 eyes in control group); 132 eyes with mixed astigmatism between 3.00 D to 6.00 D (68 eyes in experiment group, 64 eyes in control group) and 53 eyes with mixed astigmatism over 6.00 D (29 eyes in experiment group, 24 eyes in control group). They were examined with cycloplegic retinoscopy. Retinoscopy of combined positive cylinders with negative cylinders was applied in experiment group, while conventional retinoscopy was used in control group. According to the shape of neutralized image, the accuracy and facility of the axis judgement, operating time and the number of combined lens, the result of retinoscopy was classified into three grades. Grade I: The shape of neutralized image is well distributed. The axis is easy to be evaluated precisely. Operating time is less than five minutes and only need one or two piece of lens. Grade II: The shape of neutralized image is not so well distributed. The axis is not difficult to be evaluated. Operating time is from five to ten minutes and needs two or three piece of lens to combine with. Grade III: The shape of neutralized image is not so well distributed and would be interfered by the combined lens or other factors easily. The axis is difficult to be evaluated precisely. Operating time is more than ten minutes and needs more than three piece of lens to combine with.


RESULTS
In the group of mixed astigmatism less than 3.00 D, no significant difference was found between experiment group and control group. (chi(2) = 0.094, P = 0.759). However, significant difference (chi(2) = 5.546, P = 0.019) was found between the groups with mixed astigmatisms from 3.00 D to 6.00 D and very significant difference (chi(2) = 8.509, P = 0.004) was found between the groups with mixed astigmatisms over 6.00 D.


CONCLUSIONS
Retinoscopy of combined positive cylinders with negative cylinders is an effective, convenient and precise method for detection higher degree mixed astigmatisms. It's an additional assistance for the conventional retinoscopy.
Huang
Zhong-Ning
ZN
Department of Ophthalmology, Guangdong Provincial People's Hospital, Guangzhou 510080, China. xiazai@tom.com
Huang
Du-Ru
DR
Yin
Dong-Ming
DM
D000293:Adolescent; D000328:Adult; D001251:Astigmatism / Q000175:diagnosis*; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D009907:Optometry / Q000379:methods*; D015203:Reproducibility of Results; D042262:Retinoscopy / Q000379:methods*; D012680:Sensitivity and Specificity