Animals : an Open Access Journal from MDPI · 6 authors, 4 centres
This summary was generated by AI from a single paper. It has not been reviewed by a clinician and is not clinical advice. Verify against the source before acting on it.
This study provides the first CT-based morphometric reference values for the eyeball and sclerotic ring in presumed healthy loggerhead turtles. The dorsal arch of the sclerotic ring was significantly thicker than the ventral arch, possibly an adaptation to diving pressure. These findings offer a baseline for diagnosing ocular pathology in this vulnerable species.
**Background:** The loggerhead turtle (Caretta caretta) is a vulnerable marine species that faces threats from human activity, including entanglement and ingestion of hooks. Sight is crucial for their survival, yet knowledge of their ocular anatomy is limited. Turtles possess unique ocular structures such as sclerotic rings (bony ossicles) that protect the eye during diving. While CT has been used in reptile ophthalmology, no prior study has reported CT intraocular measurements in loggerhead turtles. This study aimed to establish morphometric reference values for the eyeball and its internal structures using CT.
**Methods:** Ten loggerhead turtles (19–30 kg, young to subadult) from the Tafira Wildlife Rehabilitation Center (Gran Canaria, Spain) were included. All had normal ophthalmologic examinations. CT scans of the skull were performed without sedation (using natural lethargy from room temperature 16–20°C) with a 16-slice helical scanner (120 kVp, 80 mA, 0.6 mm slice thickness). Measurements were taken in transverse, dorsal, and sagittal planes using OsiriX MD software. Parameters included lens diameter, internal and external diameters of the sclerotic ring, dorsal and ventral arch height and width, eyeball height/width/length, and attenuation (HU) of the sclerotic ring, lens, and vitreous humor. Statistical analysis used Mann–Whitney U test, two-way ANOVA, and linear regression (p < 0.05).
**Key Results:** A total of 20 eyes were measured. Mean carapace length was 41.53 cm (range 25–71.7). Mean lens diameter was 4.33 mm (range 2.6–5.6). Mean internal sclerotic ring diameter was 10.32 mm (range 6.9–14.7); mean external diameter was 16.96 mm (range 13–22). Dorsal arch height (mean 6.82 mm) was significantly greater than ventral arch height (mean 4.96 mm; p = 0.0006). Dorsal and ventral arch widths were not significantly different (2.81 vs. 2.57 mm). Eyeball dimensions: mean height 22.23 mm (range 15.9–27), width 15.77 mm (12–19.2), length 22.83 mm (16–27.9). Attenuation values: sclerotic ring mean 353.85 HU (range 203–500), lens mean 98.85 HU (81–116), vitreous humor mean 17.80 HU (7–28). No significant differences between right and left eyes. Linear regression showed significant positive correlations between carapace length and lens diameter (R² = 0.40, p = 0.00290), internal sclerotic ring diameter (R² = 0.67, p = 0.00001), external sclerotic ring diameter (R² = 0.71, p < 0.00001), ventral arch height (R² = 0.62, p = 0.00004), eyeball height (R² = 0.36, p = 0.00557), and eyeball length (R² = 0.61, p = 0.00005).
**Clinical Implications:** This study provides the first CT-based reference values for the loggerhead turtle eyeball, enabling non-invasive assessment of ocular health in live animals. The significantly thicker dorsal arch of the sclerotic ring may reflect an adaptation to water pressure during diving, as suggested in other marine turtles. The positive correlation between carapace length and ocular measurements indicates that size should be considered when evaluating ocular pathology. These reference data can aid veterinarians and conservationists in diagnosing conditions such as trauma, inflammation, or neoplasia. Limitations include a small sample size (n=10) and potential examiner error in manual CT contouring. Future studies with larger numbers and direct pressure measurements are needed to confirm functional interpretations.