Ocular

Introduction

Ocular point-of-care ultrasound (POCUS) can rapidly identify ocular emergencies, including the diagnoses of lens detachment/dislocations, retinal detachment, vitreous detachment, vitreous hemorrhage, ocular infections, the presence of foreign bodies, and secondary signs of elevated intracranial pressure. In a fast-paced clinical practice, a fully dilated ophthalmologic examination may be impractical, and studies have shown that many practitioners lack the clinical skills to perform it effectively. The benefits of performing an ocular ultrasound include ease of use, low cost, sensitivity for identifying pathology, lack of ionizing radiation, and ability to perform imaging at the bedside. POCUS offers few risks, with the exception in the setting of a possible globe rupture, and should not cause significant discomfort to the patient when done correctly. Therefore ultrasound can supplement the acute eye examination, and can accurately detect a range of important eye disorders and attempt to rule out emergent conditions.

Anatomy

To fully utilize the benefits of the ocular ultrasound, it is imperative to have an accurate understanding of the anatomy of the eye ( Fig. 5.1 ). The white, outermost layer of the eye is the sclera, which surrounds the entire globe and serves as a protective layer. The limbus creates the junction between the sclera and the cornea, which is the transparent part of the eye that covers the colored iris. The pupil allows light to enter the eye. The anterior chamber (AC) is the space between the lens and the cornea. The AC contains aqueous humor produced by the ciliary body, which is continuous with the colored iris, and the choroid, which is the vascular bed for the retina. With ultrasound, this will be the most superficial anechoic chamber. Just deep to the AC is the lens, which is a hyperechoic concave structure. The retina is the innermost layer of the eye, which contains the photoreceptors. It is often not seen unless it is detached from the posterior aspect of the globe. The posterior chamber, which accounts for approximately 80% of the eye, will be the anechoic structure deep to the lens and is filled with vitreous fluid. Finally, the optic nerve is seen as a hypoechoic structure just deep to the retina ( Fig. 5.2 ).

Examination Technique

The structures of the eye are superficial and are best visualized with a high-frequency linear array probe. A transparent dressing can be placed on top of the closed eye for patient comfort and ease of cleaning the gel after the examination ( Fig. 5.3 ). Alternatively, clean gel may be placed directly on the closed eyelid. The patient should be placed in a supine to semi-upright position to maintain the gel’s position. Slightly cooling the gel will firm it and further maintain its position. To reduce theoretical iatrogenic injury, the ocular or eye examination setting should be chosen on the ultrasound machine. The examiner can maintain probe stability while scanning by placing the scanning hand on the patient’s nasal bridge, forehead, or cheek, and use copious amounts of gel to avoid transmitting unnecessary pressure to the eye. Limiting direct pressure on the eye is important for patient comfort, as well as reducing the oculocardiac reflex, which may decrease the patient’s heart rate. Use the conventional method of transducer orientation, directing the indicator toward the patient’s right in the transverse plane and cephalad in the sagittal plane. Careful methodical scanning of all eye segments in two planes is needed to evaluate pathology. In each orthogonal plane the patient should be asked to move the eyes in every direction to allow for full dynamic evaluation of the anterior and posterior chambers, as well as confirm extraocular muscle function. Contraindications include open ocular trauma, periorbital wounds, globe rupture, or retrobulbar hemorrhage.

Indications and Pathology