[Relationships between refractive parameters: sphere, cylinder and axis].
OBJECTIVE
To analyze the relationships between refractive parameters as well as the relationship between fellow eyes in a normal population.


METHODS
Both subjective refraction and auto-refractometry data of 500 patients were prospectively recorded. Refraction data were analyzed on three rectangular coordinates in a dioptric space. WTR/ATR ratio of axis was quantified by the Cos2axis function. Enantiomorphism (mirror-image symmetry) between fellow eye axes was quantified by the absolute value of the difference between 180° and the sum of both axes.


RESULTS
Mean refraction and mean cylinder were -1.74D (+0.28D × 91.5°) and 0.81 ± 0.89D respectively. The spherical component had no significant influence on refractive astigmatism (r(s)≤ 0.07, P ≥ 0.07) except for high spherical ametropia. Eyes with spherical equivalent greater than 4D (in absolute value) demonstrated higher cylinder (1.15D vs 0.84D, P<0.001). Cylinder influenced the WTR/ATR ratio (r(s)=-0.25, P<0.001) and the enantiomorphism (r(s)=0.36, P<0.001). Age also influenced the WTR/ATR ratio (r(s)=0.27, P<0.001) and the enantiomorphism (r(s)=0.14, P<0.001). Axes were more likely WTR and enantiomorphic when the cylinder was high and the subject young. Oblique axes were less enantiomorphic (35.5° vs 20.6°, P<0.001) and were associated with lower cylinder (0.56D vs 0.98D, P<0.001). Correlation between fellow eyes was significant for cylinder (r(s)=0.66, P<0.001) and for spherical equivalent (r(s)=0.96, P<0.001). Gender had no significant influence on refraction (P>0.12) except for spherical equivalent (relative hyperopia of +0.17D, P=0.04 in females).


CONCLUSIONS
The spherical component of the refraction appears to be independent of the refractive astigmatism except for high spherical ametropia. Cylinder influences somewhat the WTR/ATR ratio of axis and the enantiomorphism. Relationships between refractive parameters are weak in comparison to the fellow eye relationships.
Service 5, centre hospitalier national d'ophtalmologie des Quinze-Vingts, 28, rue de Charenton, 75012 Paris, France; Inserm, institut de la vision, 17, rue Moreau, 75012 Paris, France. touzeau@quinze-vingts.fr
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Touzeau
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Gaujoux
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Bullet
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Allouch
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Borderie
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Laroche
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001251:Astigmatism / Q000145:classification* / Q000175:diagnosis* / Q000453:epidemiology / Q000503:physiopathology*; D003196:Computer Graphics; D005123:Eye / Q000503:physiopathology; D005260:Female; D005556:Form Perception / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D012029:Refraction, Ocular / Q000502:physiology*; D012727:Sex Characteristics; D014787:Vision Tests / Q000295:instrumentation / Q000379:methods*; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult