Study looks at degree of cyclotorsion in healthy adults
Sara Flodin MD
A significant number of healthy adults have some degree of cyclotorsion, suggesting a need to be alert for even low levels that could interfere with vision, according to Dr Sara Flodin, SU Mölndal Gothenburg, Sweden.
Speaking at the World Congress of Paediatric Ophthalmology and Strabismus in Hyderabad, India, she presented her research studying the standard reference range of cyclotorsion in a healthy adult population. She explained that although literature shows different methods for measuring cyclotorsion, none are standardised and very little is documented about the recommended method of use, the reproducibility and the reliability of measurement results.
Since subjective torsion testing records the response of perceived torsional orientation of an object, and binocular single vision is affected by torsion, it is important to know how much torsion is significant and how much is present in adults in general.
The aim of her research, therefore, was to find out the degree of cyclotorsion in a healthy adult population and to establish a general reference range to aid in clinical management of patients suffering from disruption of binocular viewing and image fusion. Some 120 volunteers (60 males and 60 females) between the ages of 18 and 69 years were included to establish a statistically significant reference interval, in accordance with the guidelines of the Clinical and Laboratory Standards Institute (CLSI). Healthy, non-strabismic adults with normal vision were included.
Patients unable to speak or understand Swedish, those with manifest strabismus, previous ocular surgery, diplopia, medications that may affect the eyes in any way or with neurological or circulatory illnesses were excluded. This, she said, ensured a naive population, as none of the subjects had undergone orthoptic investigations previously.
The Single Maddox Rod
Cyclotorsion was assessed using the synoptophore and the single Maddox rod, and a positive value was assigned to intorsion and a negative value to extorsion. Healthy non-strabismic adults in all age groups showed low values of cyclotorsion in the study, with a mean value for the whole sample of -1 degree for both methods. The standard reference range of cyclotorsion for men and women was roughly between -0.8 and -1.6 on single Maddox rod and -0.8 and -1.7 on synoptophore. The only significant difference was an increase in excyclotorsion with age (p=0.026).
Dr Flodin concluded that low levels of cyclotorsion are to be expected upon clinical investigation of non-strabismic individuals. A small increase in cyclotorsion, of even two degrees or less, may be sufficient to disrupt the ability to fuse binocular images. She also said that the study demonstrated the importance of investigating cyclotorsion in patients experiencing fusional problems. When values are outside the reference ranges, cyclotorsion and other fusional components need to be evaluated, she emphasised.
Sara Flodin: firstname.lastname@example.org