© 2007 American College of Veterinary Ophthalmologists Veterinary Ophthalmology (2007) 10, 1, 2–5 Blackwell Publishing Inc Postnatal development of canine axial globe length measured by B-scan ultrasonography N. Tuntivanich,* Simon M. Petersen-Jones,* Juan P. Steibel,† C. Johnson* and Janice Q. Forcier* *Department of Small Animal Clinical Sciences, College of Veterinary Medicine, †College of Agriculture and Natural Resources, Michigan State University, East Lansing, MI 48824, USA Abstract Objective The objectives of this study were to document the development of axial globe length (AGL) in normal mesocephalic cross-bred dogs between 2 and 52 weeks of age, to determine a relationship between AGL and age, and derive an equation to predict AGL in normal mesocephalic cross-bred dogs. Animals studied and procedure The AGL of twenty normal mesocephalic cross-bred dogs was measured at 12 time points from 2 to 52 weeks of age using B-scan ultrasonography. Results The mean (± SEM) AGL increased from 12.65 mm (± 0.18) at 2 weeks of age to 19.52 mm (± 0.18) at 52 weeks of age. The correlation between AGL and age was evaluated by fitting possible variables to a regression pattern. A linear model of natural logarithmic-transformed value of AGL (mm) and age (week) was established. Side (left or right eye) and gender did not correlate with development of AGL. Conclusions A reverse transformation of the formula can be used to predict AGL in mesocephalic cross-bred dogs: AGL = 10.847 * age in weeks 0.1653 . Key Words: axial globe, B-scan ultrasonography, dog Address communications to: S. M. Petersen-Jones Tel.: (517) 353-3278 Fax: (517) 355-5164 e-mail: peter315@cvm.msu.edu INTRODUCTION The eyes of dogs are not fully developed at birth: over the first 2 to 3 months of age the canine eye continues to develop and becomes adult-like in function. 1–3 During this maturation period there is an increase in axial globe length. Ekesten and Torrång documented the difference in axial globe length (AGL) of Samoyed dogs aged between 2 months and 13 years. 4 They found that in the young dogs there appeared to be an initial phase of a rapid increase in AGL, after which the change in axial globe length with age tended toward a plateau. The mean AGL in their study ranged from 17 to 22 mm. The axial globe length (± SD) in adult dogs has been reported by a number of authors and in those reports the mean AGL ranged from 20 to 21.91 mm. 5–8 The authors of this current study could not find any published studies that record the change in axial globe length in puppies prior to 2 months of age. Ultrasonography is commonly used to measure AGL in vivo. The reflection of ultrasonic waves generated from a piezo- electric transducer occurs at the different tissue interfaces of the eye such as at the corneal surface, anterior lens surface, posterior lens surface, and retinal surface. The reflected waves are captured, amplified and processed prior to being transformed into an ultrasonographic image. A-scan ultrasonic image is illustrated as vector lines (spikes) derived from reflections of ultrasonic waves from the different ocular tissue inter- faces and is often used to measure ocular dimensions. A two- dimensional B-scan image provides anatomic cross-sectional features of the eye and is widely used for clinical diagnosis. Previous studies have shown that B-scan measurement is reasonably accurate for AGL determination. 6,9 Additionally, it provides an image that is easy to interpret. 6 The purpose of this present study was to document the development of AGL using B-scan ultrasonography in mesocephalic cross-bred dogs aged between 2 weeks and 1 year of age and then to develop a model to describe the relationship between AGL and age. MATERIALS AND METHODS Animals Axial globe length was measured in twenty cross-bred dogs at 12 time points between 2 weeks and 1 year of age. Dogs were kept in the MSU College of Veterinary Medicine’s vivarium under standard conditions of 12 h light/dark cycles and were monitored for the period of the experiment for the presence or development of ocular abnormalities. Dogs were cared for in accordance with the humane principles set forth in the Public Health Service Policy on Humane Care and Use of