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Title	Relative frequencies of congenital colour vision deficiencies seen at the Ghent University Hospital
Abstract Nr.	P016

Purpose	As a group, congenital colour vision (CV) deficiencies are rather frequent. Traditionally they include trichromatic deuteranomaly (DA), protanomaly (PA) and the dichromatic deuteranopia (D) and protanopia (P). Tritanomaly (TA) and tritanopia (T), blue cone monochromacy (BCM) and complete achromatopsia (CA) are all less frequent. Here, results of CV screening of such patients seen during 49 years at the Ghent University Hospital (GUH) are presented.
Methods	A total of 3289 patients (>99% males) referred because of problems with CV were examined from 1955 until 2004. To evaluate a potential referral bias prior to a change in the Belgian law (RD of 23/03/1998) allowing patients with P to drive from then onwards, patients examined after the introduction of that law were also analysed as a separate subgroup. All patients were examined using standard CV tests under C-light, including PIC-plates, ranking tests & anomaloscopy.
Results	The breakdown of the 3289 patients in decreasing order is as follows: 42% DA, 20% P, 19% D, 13% PA, and <1% CA, unknowns, BCM, TA, and 4% normals. The figures for 215 patients seen after introduction of the RD of 23/03/1998 are: 35% DA, 22% P, 20% PA, 14% D, 1% CA & 7% normals.
Conclusion	Relative frequencies of congenital CV deficiencies in patients seen at the GUH show a relative underrepresentation of DA and an overrepresentation of P & D. This is true when evaluating both total numbers and the numbers after a change in Belgian law allowing P patients to drive. Consequently, the relatively mild character of DA may be a more important referral bias.

Author 1

Last name	UVIJLS
Initials	A
Department	Ghent Univ Hospital
City	Ghent

Author 2

Last name	DE BIE
Initials	S
Department	Ghent Univ Hospital
City	Ghent

Author 3

Last name	KESTELYN
Initials	P
Department	Ghent Univ Hospital
City	Ghent

Author 4

Last name	LEROY
Initials	BP
Department	Ghent Univ Hospital
City	Ghent