Survey of retinal haemorrhages in neonatal thoroughbred foals

Abstract

Twenty-seven of 167 neonatal thoroughbred foals (16 per cent) were found to have retinal haemorrhages after a careful examination of the entire fundus. Experience in differentiating haemorrhages from other lesions, and the selection of foals from normal populations, were considered to have an important effect on their apparent incidence. Bilateral haemorrhages were more common and there was a significantly higher incidence in female foals. The numbers of haemorrhages ranged between one and 20; 36 per cent of eyes with retinal haemorrhages had the small punctate type and 56 per cent had the splash-like form. There was no change from one type of haemorrhage to another, and the patterns of resolution were similar. The haemorrhages were in the tapetal fundus, except two that were recorded in the optic disc, and they resolved within 10 days. No short- or long-term ocular or neurological effects of the retinal haemorrhages were detected, and they were not related to the incidence of abnormal foal behaviour.

Ophthalmic lesions in neonatal foals evaluated for nonophthalmic disease at referral hospitals

“…The percentage of foals with retinal hemorrhages (11.4%) in the present study was lower than that previously reported (16%) in healthy Thoroughbred foals in New Zealand 19 ; however, the 95% confidence intervals for the 2 populations overlap, which suggests the prevalence may not be different between these groups. Retinal hemorrhages were previously thought to be associated with NMS, but more recent investigation indicated that this is more common in larger foals and foals born to dams experiencing dystocia, and is not associated with the development of NMS.…”

Ocular findings in healthy newborn foals according to age

“…Results of this study are in general agreement with previous ocular descriptions of the newborn foal at later periods of their neonatal age (Barnett 1975; Latimer et al . 1983; Enzerink 1998; Munroe 1995, 1999, 2000a,b; Turner 2004). However, in this study, new information on the ocular characteristics of early newborn foals is added comparing their ocular findings with those observed in foals at later ages.…”

“…Retinal haemorrhages in foals have been frequently related to hypoxic‐ischaemic encephalopathy but have been commonly found in otherwise perfectly normal foals, suggesting that they may be of no clinical significance (Munroe and Barnett 1984; Munroe 2000b). Although the aetiology of retinal haemorrhages has not been clarified, different authors consider that they are due to trauma of birth (Johnson and Rossdale 1975; Bistner 1984; Whitley 1990; Munroe 2000b). It has been demonstrated that foals weighing more than 51 kg are at increased risk of having retinal haemorrhages (Munroe 2000b).…”

“…Although reports on congenital and acquired ocular abnormalities in foals are common, publications on normal ocular characteristics in healthy equine neonates have been less frequently reported (Latimer et al . 1983; Munroe 1995, 1999, 2000a,b). Among these reports, complete studies of the biological eye's characteristics in foals younger than 6 days (early neonates) are lacking.…”

Posterior segment diseases

“…Intra-and subretinal haemorrages occur in both normal neonatal foals and foals affected with perinatal asphyxia syndrome. They resolve over several days and are of no functional significance (Munroe 2000b).…”