Gentle restraint, using a head halter or a similar device, may provide enough support to perform a cursory examination. For smaller species or fawns, wrapping them in a blanket or towel might offer enough restraint. Generally, ophthalmic examinations performed with animals under manual restraint are only cursory and should be regarded as a screening process. If specific ophthalmic findings are identified and determined to be significant enough to warrant further evaluation, sedation should be considered to accurately assess the findings, perform additional diagnostic testing, establish a diagnosis then implement appropriate and targeted medical management or surgical intervention.

While cursory ophthalmological examinations and screening of the eyes and adnexa from a distance can be performed without restraint and sedation, detailed examinations and ophthalmological procedures require physical restraint with sedation, immobilisation or anaesthesia (Figure 27.2; Villar et al. 2020). Traditionally, sedation of cervids relied on administration of single-drug α-2 adrenergic receptor agonists or opioids; however, newer protocols rely on combinations of different classes of anaesthetic drugs, which allow for the reduction of individual drug doses due to symbiotic effects and lessens the risk of unwanted side effects. Chapter 3 provides details of restraint and sedation procedures, and most techniques utilised for the examination and treatment of other body systems also apply to ophthalmological procedures. The authors are most familiar with the handling and examination of white-tailed deer using combinations of Telazol/Zoletil (tiletamine and zolazepam) and xylazine (TX) or butorphanol, azaperone and medetomidine (BAM). Following intramuscular injection, TX and BAM result in smooth and rapid onset of sedation within 5–10 minutes, which is more reliable and quicker than sedation with xylazine alone (Miller et al. 2004, 2009; Warren et al. 1984).

At typical doses, the depth of sedation achieved with TX or BAM is sufficient for detailed examination of the eyes and provides excellent eyelid relaxation. While TX or BAM both provide sufficient immobilisation durations to facilitate thorough ophthalmological examinations and procedures, TX sedation tends to diminish in depth after 30–45 minutes and requires administration of additional sedatives (e.g. half of the original TX dose or 1 mg/kg of ketamine IV) for longer procedures. In contrast, the duration of BAM sedation is considerably longer and reversal of sedation is required under most circumstances. A notable advantage of using BAM is the ability to completely reverse its sedative effects using naltrexone and atipamezole, which is not possible with TX. When TX sedation is reversed using an α-2 adrenergic receptor antagonist, such as yohimbine, tolazoline or atipamezole, the components of tiletamine and zolazepam occasionally result in resedation and animals should be maintained away from unsafe environments, such as bodies of water or steep drops. Another disadvantage of TX is the possibility of hyperthermia, requiring animals to be handled expediently and in cool environments. In contrast, the risk of development of hyperthermia is lower for BAM, which is, however, associated with an increased risk for hypoxia (Miller et al. 2009).

When adequate handling facilities are available, either drug combination can be administered by intravenous injection using approximately half of the intramuscular dose. However, in many cases drug delivery by dart gun is necessary. While generally considered to be safe, use of a dart gun increases the risk of injury and results in less reliable drug delivery.

While not specifically evaluated in deer, unwanted ocular side effects associated with some anaesthetic drugs are reported in other veterinary species, including changes in intraocular pressures (IOPs) and altered tear production. For example, ketamine and other dissociative anaesthetics increase IOPs; however, these effects can be reduced by the administration of benzodiazepines (Pierce-Tomlin et al. 2020). A study in white-tailed deer reported severely diminished tear production in animals immobilised with tiletamine, zolazepam and xylazine treatment (Villar et al. 2020), which is also possible when higher doses of α-2 adrenergic receptor agonists or anaesthetic combinations are administered (Raušer et al. 2022). These effects are often not clinically relevant but should be considered when large doses of anaesthetic drugs are necessary or when sudden increases in IOPs are contraindicated. In calm or co-operative deer, simple ophthalmological procedures can be performed using mild sedation protocols; eyelid relaxation and analgesia can be provided using local or regional nerve blocks (e.g. auriculopalpebral, supraorbital or infratrochlear block) as utilised in domestic ruminants (McMullen and Passler 2021). For example, one report described the removal of the third eyelid of a domesticated reindeer due to squamous cell carcinoma, using sedation and regional nerve blocks (Lawrence-Mills et al. 2023). In animals that are more fractious, deeper sedation or immobilisation may be necessary and local or regional anaesthetic blocks are used to provide analgesia for painful procedures.

Choose a calm, quiet and dimly lit area to reduce stress and to allow the pupil to dilate to facilitate a more thorough examination.