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Night Blindness in the Appaloosa (CSNB)

Introduction to CSNB Educational Pages

Welcome to the main page of the CSNB education section of our website. This is a general information page that provides a definition of CSNB and a summary of the 2005-06 CSNB study, including the abstract from the scientific paper itself. Simply scroll further down this page to read these items.

There are also five other linked resource pages on this part of the site, dealing with frequently asked question, inheritance, management of affected horses, general equine vision, and background information on the CSNB study. You will find live links to them further down this page, under the heading "Resources on This Website".

We hope that you find the information we have prepared for you to be helpful.

Sheila Archer
The Appaloosa Project

What is CSNB?

CSNB stands for “congenital stationary night blindness”. More commonly referred to as night blindness, CSNB is the name given to any disease that is typified by:

a) impaired/absent night vision
b) present at birth
c) inherited
d) non-progressive

This term does not represent a single disorder. There are several forms of CSNB in humans and other animals. The above are the features that all these unique, yet similar types of CSNB share.

Impaired night vision is a general description. Some forms of CSNB involve extremely impaired vision, while others are less severe. They all involve some degree of lack of rod function, thus the term “night blind”.

The form of CSNB found in the Appaloosa is the subject of the information pages on this website. Please read on to find out more about it, how it was discovered and the research being conducted to study it further.

CSNB affected patterns

Is Appaloosa-specific CSNB connected to a particular coat pattern?

The 2005-06 study by Sandmeyer et al revealed that CSNB is associated with Appaloosa coat patterning of a specific type. Appaloosas with coat patterns indicating they are homozygous for LP are affected. The above diagram shows these patterns. Appaloosas that are heterozygous for LP are not affected by CSNB. Horses that are true solid non-characteristic Appaloosas, with no dominant copies of LP, are not affected by CSNB either.

For more information on the research that was done to establish this connection, readers will want to read the summary of the research paper, or the entire document (see below on this page). More information relating to coat pattern and CSNB can also be found on the Frequently Asked Questions and Inheritance of CSNB pages.

Resources on This Website:

The scientific paper quoted below is a technical document written primarily for the veterinary ophthalmologist. On the Appaloosa Project website you will find information about CSNB presented in layman's terms, prepared specifically for breeders and enthusiasts and. Our information pages have been written by Dr. Lynne Sandmeyer, Sheila Archer and Dr. Rebecca Bellone. Just click on the title of the section you wish to read:

1. Frequently Asked Questions about CSNB in the Appaloosa
- 22 questions about CSNB and the research that was done to investigate it

2. Inheritance Information for Appaloosa-specific CSNB
- Diagrams showing various types of crosses and the probable outcomes, using Punnett Squares

3. Management of Night Blind Horses
- Practical guidelines for owners, breeders and anyone else working with CSNB-affected Appaloosas

4. Equine Vision and Management of Vision Problems in Horses
- A survey of the horse's visual system, common vision problems and their management

5. Background Information on CSNB Research
- A historical overview of research on CSNB in the Appaloosa and a description of how the latest research came about, and why.

2005-06 CSNB Study - The Paper and the Findings

In 2005-06, Sandmeyer, Breaux, Archer and Grahn conducted a scientific investigation of night blindness in the Appaloosa. The entire paper that resulted from this study is now in print, and can be obtained by following this link (note that the publisher charges a fee for the full text):

Veterinary Ophthalmology, Volume 10 Issue 6 Page 368-375, November 2007
Journal of the American College of Veterinary Ophthalmology (ACVO), published by Blackwell Science.

The summary, known as an Abstract, appears below:

Clinical and electroretinographic characteristics of congenital stationary night blindness in the Appaloosa and the association with the leopard complex

Lynne S Sandmeyer*, Carrie B Breaux*, Sheila Archer†, Bruce H Grahn*

* Department of Small Animal Clinical Sciences, Western College of Veterinary Medicine University of Saskatchewan, 52 Campus Drive, Saskatoon, Saskatchewan, S7N 5B4, Canada, and † Moose Jaw, Saskatchewan S6H 7W6, Canada.

Lynne S. Sandmeyer DVM, DVSc, DACVO.
Carrie B. Breaux DVM.
Sheila Archer BSc Hons
Bruce H. Grahn DVM, ACBP, DACVO

Objective: To determine the prevalence of congenital stationary night blindness (CSNB) in a population of Appaloosa horses in western Canada, investigate the association with the leopard complex of white spotting patterns, and further characterize the clinical and electroretinographic aspects of CSNB in the Appaloosa. Animals studied: Three groups of ten Appaloosas were studied based on coat patterns suggestive of LpLp, Lplp, and lplp genotype. Procedures: Neurophthalmic examination, slit-lamp biomicroscopy, indirect ophthalmoscopy, measurement of corneal diameter, streak retinoscopy, scotopic and photopic full-field flash and flicker ERGs were completed bilaterally. Results: All horses in the LpLp group were affected by CSNB, while none in the Lplp or lplp groups were affected. The LpLp and Lplp groups had significantly smaller vertical and horizontal corneal diameters compared to lplp group. Median refractive error was zero for all groups. Scotopic flash ERGs in the LpLp (CSNB-affected) group were consistent with previous descriptions. The CSNB-affected horses had significantly longer photopic flash a-wave implicit times, greater a-wave amplitudes, and lower b-wave amplitudes compared to the Lplp and lplp (normal) groups. No differences were present in photopic flicker amplitude or implicit times. Scotopic flickers in the CSNB-affected horses were markedly reduced in amplitude and abnormal in appearance. No differences were noted in oscillatory potential (OP) implicit times, however amplitudes of some OPs were reduced in CSNB-affected horses. There were no differences in scotopic and photopic flash or flicker ERGs or OPs between the normal groups. Conclusions: CSNB was present in 1/3rd of horses studied and there is a significant association between CSNB and the inheritance of two Lp alleles. ERG abnormalities support the hypothesis that CSNB is caused by a defect in neural transmission through the rod pathway involving the inner nuclear layer.

How To Contact Us With Questions

If after reading the CSNB information pages on this site you have a question for our research team about CSNB, you are invited to address them directly to the authors via the Appaloosa Project's "Electronic Classroom". Dr. Sandmeyer and Ms. Archer have both agreed to answer questions about the CSNB research and its practical implications in that venue.

Please note that to join the "Electronic Classroom", you will need to subscribe to this website if you are not already a member.

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Night blind mares

Created on 09/08/2007 02:20 PM by SheilaArcher
Updated on 04/21/2011 02:55 PM by SheilaArcher
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