Ocular findings in healthy newborn foals according to age

Abstract

Summary The aim of this prospective observational clinical study was to carry out a descriptive ophthalmic investigation in healthy newborn foals for the establishment of normal ocular anomalies found during the whole neonatal period. To date there have been no studies specifically addressing the normal ocular findings and variations of the eye and adnexa in foals during the neonatal period. Knowledge of the ocular characteristics at this early age will help equine practitioners to better identify ocular abnormalities. A detailed ophthalmic examination was performed by boarded ophthalmologists on all admitted healthy newborn foals. There were 52 foals included in the study grouped into those that were 1‐day‐old, younger than 5 days, aged 6–15 days and 16–21 days. Menace response was found to be absent in foals younger than 15 days. Pupillary light reflexes were present in all foals but were slower and incomplete in 14/14 1‐day‐old foals (100%) and in 7/21 foals aged 2–5 days (33%). Palpebral reflexes were positive in all foals. Ventromedial strabismus was bilaterally present in 8/14 1‐day‐old foals (57%) and in 4/21 foals aged 2–5 days (19%). Conjunctival congestion was observed in all groups. Conjunctival haemorrhages, perilimbal vascular ring, lens suture opacities and multifocal tapetal haemorrhages were exclusive findings from 1‐day‐old foals, with an incidence of 36, 21, 36 and 29%, respectively. The means of IOP readings were similar in all age groups. Hyaloid artery remnant and optic nerve head congestion were present in all 1‐day‐old foals (100%), decreasing in incidence with age. Ocular findings in new neonates are different from those observed in older neonates and should be considered when examining the foal's eye. Findings described in this study will help equine practitioners to more accurately diagnose discrete or unusual pathological changes in the newborn foal's eye according to their age.

Comparison of two rebound tonometers in healthy horses

“…A recent study suggested that IOP may decrease with age also in miniature donkeys 22 . Newborn foals have been reported to have IOP readings similar to adult horses 27,28 . While in this study, IOP was not found to be associated with age, all of the horses were adults and only two were older than 15 years (data not shown).…”

Age‐associated changes in the equine flash visual evoked potential

“…Menace responses were inconsistent in newborn foals in accordance with what has been described in normal foals during the first weeks of life. [21][22][23] Two positive wavelets (P2 and P4) and two negative wavelets (N1 and N2) were identified in all FVEP recordings, while additional wavelets (P1, N2a, P3, and P5) were observed in some recordings in accordance with what was seen in our previous study. 19 There were no specific differences when comparing tracings between age groups in this aspect.…”

“…32 However, a normal menace response is often not seen until up to 2 weeks postpartum, whereas subcortical reflexes, such as the pupillary light and dazzle reflexes, are present at birth in the foal. [21][22][23] We found that all newborn foals included in the study lacked normal menace responses, although their FVEP waveforms appeared mature-like. It is known that the efferent pathway of the menace response is conveyed through cerebellum and facial neurons in the brainstem, 33 and the lack of menace response may also depend on the immature cerebellum in the newborn foal rather than an immature input to or processing in the visual cortex alone.…”

“…Most foals move their heads away from a threatening gesture indicating that they can perceive the stimulus, although the quality of vision is difficult to assess . However, a normal menace response is often not seen until up to 2 weeks postpartum, whereas subcortical reflexes, such as the pupillary light and dazzle reflexes, are present at birth in the foal . We found that all newborn foals included in the study lacked normal menace responses, although their FVEP waveforms appeared mature‐like.…”

Ocular abnormalities in healthy Standardbred foals

“…A comprehensive evaluation of these ocular features is paramount when examining the neonate 1 . The neonatal pupil is initially round in shape 2,3 and becomes horizontal and elliptical throughout the first week of life 3,4 . The globe of many foals shows a mild ventromedial orientation at birth 3 but acquires a normal position after several days 3 or even later 5 .…”