CHC
Congenital Hereditary Cataract
Testing method
Slit-lamp biomicroscopic examination of the lens following pupil dilation. The nuclear position and characteristic appearance distinguish CHC from other forms of cataract. Litter screening and early examination are recommended, given the congenital nature of the condition.
What is congenital hereditary cataract?
Congenital hereditary cataract (CHC) is a form of inherited cataract that is present from birth or detectable in very early life. Unlike the non-congenital hereditary cataracts that develop in adult dogs, CHC is a developmental abnormality of the lens that occurs during gestation or in the immediate neonatal period.
In the Miniature Schnauzer — the breed currently certified for CHC under the BVA scheme — the cataract is primarily nuclear in position, affecting the centre of the lens. The opacity may vary in density and is typically bilateral and similar in both eyes. Associated abnormalities including posterior lenticonus (a conical protrusion of the posterior lens capsule) and microphakia (an abnormally small lens) may also be present.
Distinguishing CHC from normal lens changes in Miniature Schnauzers
An important point specific to the Miniature Schnauzer: temporary opacification of the equatorial suture lines is a normal finding in some puppies of this breed and is not a sign of CHC. These temporary opacities disappear by 9 to 12 months of age and are of no clinical significance. An experienced panellist will be able to differentiate these transient suture line opacities from true congenital hereditary cataract.
Breeds affected
Congenital hereditary cataract is currently certified under the BVA scheme in the Miniature Schnauzer. Note that the Miniature Schnauzer is also certified for non-congenital hereditary cataract (HC), which is a separate condition with a different age of onset and lens appearance. Both conditions may be assessed at the same examination.
What the examination involves
The examination requires pupil dilation to allow full visualisation of the lens. Slit-lamp biomicroscopy is used to assess the position, pattern, and density of any lens opacity. Early examination is recommended, ideally as part of litter screening or at first veterinary examination, given the congenital nature of the condition.