# Anterior Segment Measurements in Normal Cats Using Ultrasound Biomicroscopy

## TL;DR

This study provides detailed ultrasound measurements of healthy cats' eye structures to help diagnose eye diseases more accurately.

## Contribution

The study establishes normative ultrasound biomicroscopy reference values for the feline anterior segment.

## Key findings

- Most anterior segment measurements in cats were consistent across sex, body weight, and age.
- Reference values for corneal thickness, anterior chamber depth, and ciliary body parameters were established.
- Sex and body weight showed limited associations with specific iris and anterior chamber measurements.

## Abstract

Cats can develop a variety of ocular diseases, but early diagnosis is often challenging because detailed reference information on the normal internal structure of the feline eye is limited. This study used ultrasound biomicroscopy, a high-resolution imaging technique, to quantitatively evaluate the anterior segment of healthy cats, including the cornea, anterior chamber, iris, and ciliary body. In addition to establishing normal reference values, we assessed whether these measurements were influenced by sex, body weight, or age. Most parameters were consistent across these factors, although limited associations were identified for specific iris-related and anterior chamber measurements. These normative data provide a practical reference for veterinarians and may support earlier detection and more accurate evaluation of anterior segment disorders such as glaucoma, uveitis, and iris-related diseases in cats.

Establishing baseline ultrasound biomicroscopy (UBM) measurements of the feline anterior segment is essential for accurate evaluation of ocular diseases. This study aimed to establish normative UBM parameters in clinically normal cats and to assess the influence of sex, body weight, and age on these measurements. Twenty eyes from twenty healthy adult cats were examined using a standardized UBM protocol under general anesthesia to ensure consistent positioning and optimal visualization. Quantitative measurements were obtained for corneal, anterior chamber, iris, ciliary cleft, and ciliary body parameters. The mean perilimbal corneal thickness was 0.59 mm, anterior chamber depth was 4.11 mm, and peripheral anterior chamber depth was 3.11 mm. The angle-opening distance and iridocorneal angle measured 1.73 mm and 28.89°, respectively. Ciliary cleft parameters included a width of 1.22 mm, length of 2.07 mm, and area of 1.10 mm2. Longitudinal and combined longitudinal–radial ciliary body thicknesses were 0.52 mm and 0.78 mm, respectively, while ciliary body axial length and ciliary process scleral angle averaged 2.01 mm and 58.98°. Iris base width and iris middle width measured 0.35 mm and 0.54 mm, respectively. Sex-based analysis revealed significant differences in peripheral anterior chamber depth and ciliary cleft width, whereas body weight showed positive correlations with iris thickness parameters. No significant associations were identified between age and any anterior segment measurements. These findings establish comprehensive normative UBM reference values for the feline anterior segment and provide a quantitative anatomical framework for future clinical and disease-oriented studies in feline ophthalmology.