The Eye and Orbit Notes pdf PDF

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The Eye and Orbit: Describe, with the aid of a diagram, the normal anatomy of the eye. - Anatomy and pathology of the eye are easily and consistently demonstrated with high-resolution ultrasound. - Vitreous Body: composed of an aqueous gel consisting of 99% water. Normally anechoic. - Sonographically the normal retina, choroid and sclera present an inseparable echogenic concavity demarcating the posterior aspect of the globe. - Hypoechoic nerve emanates from the posterior aspect of the globe. This is surrounded by the echogenic retrobulbar fat. ! ! Sclera and Cornea: - The outer coat of the eyeball - Tough and fibrous, comprises the sclera and cornea - Almost avascular. !

- Sclera is the dense connective tissue that forms the white part of the eye and surrounds the cornea. Extends from the cornea to the optic nerve. - Sclera is continuous with the stromal layer of the cornea. - Sclera regarded as a cup-like expansion of the dural sheath of the optic nerve. On ultrasound, is resolvable from the inner layers of choroid and retina. !

- Cornea is the clear front surface of the eye. - Lies directly in front of the iris and pupil and allows light to enter the eye.

- Cornea has 5 layers. ! ! Sclera Function:

- The sclera, along with the intraocular pressure (IOP) of the eye, maintains the shape of the eyeball.

- The tough, fibrous nature of the sclera also protects -

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the eye from serious damage — such as laceration or rupture — from external trauma. The sclera also provides a sturdy attachment for the extraocular muscles that control the movement of the eyes.! ! Cornea Function: Allows light to enter the eye for vision. Provides approx 65-75% of the focussing power of the eye. The remainder of the focusing power of the eye is provided by the crystalline lens, located directly behind the pupil.! ! Conjunctiva: Bulbar conjunctiva - This portion of the conjunctiva covers the anterior part of the sclera (white of the eye). The bulbar conjunctiva stops at the junction between the ssclera and cornea; it does not cover the cornea. Palpebral conjunctiva - This portion covers the inner surface of both the upper and lower eyelids. (Another term for the palpebral conjunctiva is tarsal conjunctiva.)! !

Conjuctiva Functions:

- The primary functions of the conjunctiva are:!

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• Keep the front surface of the eye moist and lubricated.! • Keep the inner surface of the eyelids moist and lubricated so they open and close easily without friction or causing eye irritation.! • Protect the eye from dust, debris and infection-causing microorganisms. ! ! Uvea: The uvea is the pigmented middle layer of the eyeball. It has three segments: the iris, the ciliary body and the choroid.! ! Iris: The iris of the eye is the thin, circular structure made of connective tissue and muscle that surrounds the!pupil. The colour of our eyes is determined by the amount of pigment in the iris.! ! Ciliary Body: The second part of the uvea is the ciliary body. It surrounds the iris and cannot be seen because it's located behind the opaque sclera.! ! Choroid: The posterior portion of the uvea is the choroid, which is sandwiched between the tough outer sclera of the eyeball and the retina in the back of the eye.! ! Iris, Ciliary Body and Choroid Function:! Iris: In addition to giving the eye its colour, the iris acts like the diaphragm of a camera and controls the size of the pupil. One muscle within the iris constricts the pupil in bright light (full sunlight, for example), and another iris muscle dilates (enlarges) the pupil in dim lighting and in the dark.! ! Ciliary Body: The ciliary body holds the lens of the eye in place. It is connected to the lens with a network of many tiny ligaments (called ciliary zonules or zonules of Zinn) that suspend the lens in place behind the pupil. The ciliary body also secretes the clear aqueous fluid that fills the space in the anterior segment of the eye between the!cornea and the iris and lens, and it contains the muscle that controls!accommodation!of the eye.! ! Choroid: The posterior portion of the uvea — the choroid — contains many tiny blood vessels and has the vital role of nourishing the retina. ! ! Pupil: The pupil is the opening in the center of the iris. The function of the pupil is to allow light to enter the eye!so it can be focused on the!retina to begin the process of sight.! ! Retina: The retina is the sensory membrane that lines the inner surface of the back of the eyeball. It's composed of several layers, including one that contains specialized cells called photoreceptors.! ! Retina Function: Photoreceptor cells take light focused by

the!cornea!and lens and convert it into chemical and nervous signals which are transported to visual centers in the brain by way of the optic nerve.! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !

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Identify the orbital anatomic structures as demonstrated on ocular ultrasound. From outer to inner:! • Sclera (S)! • Choroid (C)! • Retinal Pigment Layer (RPE) - This is separated from the neural layer by a potential space - the sub retinal space. The retinal pigment epithelium becomes firmly fixed to the choroid, but its attachment to the neural retina is not so firm. ! • Retinal neural layer (R) - in contact with the vitreous humour. ! ! NOTE: On ultrasound, these layers cannot be well distinguished.! ! Structures Identified: Anterior and posterior surface of cornea - separated by sonolucent interval anterior chamber = sonolucent iris = visible anterior and posterior surface of lens—lens = homogeneous vitreous humour = sonolucent echoes from retina, choroid and sclera merge enhancement seen behind eye optic nerve is seen as a sonolucent tube! ! Describe the sonographic appearances of the normal eye.! ! ! ! ! ! ! !

! ! ! ! ! ! ! ! ! ! ! What are the indications for eye scanning?

- Opaque light-conducting media, making direct vision by ophthalmoscopy difficult or impossible. - Suspected intraocular tumour: solid lesions are readily visualised, localised and measured by ultrasound.

- Differentiation between serous and solid retinal detachment. It is not always possible to determine ophthalmoscopically whether a detachment is concealing a tumour. The subretinal area is clearly demonstrated by ultrasound. Examination of the vitreous. Localisation of foreign bodies. Ocular measurements (biometry, using A-scan). Proptosis. Doppler investigation of orbital vascular disease and tumours !

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Scanning Technique:

- High resolution, small parts transducer (10 or 7.5MHz) is ideal. - Cleanliness is important with equipment that comes into contact with the eye/eyelid in order to -

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prevent cross infection or irritation. NOTE: with a penetrating eye injury, sterile conditions must be maintained. Patient is placed supine with eyes closed. Moderate amount of sterile gel placed on eyelid. Each eye evaluated separately:! • First the central portion the globe with patient looking directly at the probe! • Second, the peripheral aspects of the globe with the patient performing standard ocular movements. Examination performed in the axial and sagittal plane. ! ! ! ! Which are the most common ocular tumours? Malignant melanoma of the choroid is the most common primary intraocular tumour in adults. 85% of ocular melanomas arise form the choroid and 15% from the ciliary body. Melanoma most frequently between 50-60. Rare below 30 and above 80. Most tumour arise posterior to the equator of the eye. Usually single and unilateral. ! Ultrasound appearances of choroidal melanoma: Lenticular shaped mass deeply embedded in and arising from the choroid. Moderately reflective, may give rise to some acoustic shadowing Less commonly tumour can be poorly reflective and may have a cystic component. Some have a bilobed or cottage loaf shaped appearance. Some tumours demonstrate choroidal excavation - where low amplitude tumour cell echoes replace and enlarge the choroid. Small melanomas may be echo free (can make degenerative lesions difficult). Clue is given if lesion identified lying deep to the choroid and serial examinations show growth. Colour doppler scanning may help differentiate melanoma from sub retinal haemorrhage by demonstrating blood flow within the lesion (tumour vessels show as pulsating channels or lakes of colour — care must be taken so that blood flow in overlying retina not mistaken for tumour circulation). ! ! NOTE: Not all tumours show vascularity, especially if less than 3mm. !

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What are the most common causes of vitreous haemorrhage? Small haemorrhages dispersed throughout the vitreous may be difficult or impossible to demonstrate, but larger bleeds are more easily seen as widespread, low intensity echoes with marked after movements on dynamic scanning. Subarachnoid haemorrhage (terson’s syndrome) or from blunt trauma. In these cases, the red blood cells will sediment and compact near the posterior hyaloid surface of the detached vitreous and scanning shows echoes or increasing intensity. ! ! How does dynamic scanning help to differentiate between a retinal detachment and a vitreous membrane? The moderately collapsed gel sites of vitreoretinal adhesion are not always obvious on ultrasound scanning until dynamic testing is used and positions of restricted movement identified. Similarly, fine vitreous strands, usually joining the gel mass to the posterior pole, are not seen until eye movement demonstrates gel tethering. The characteristic motion of vitreous and retina normally enables these structures to be distinguished. However, if the posterior hyaloid surface is thickened and attached to the optic nerve head, very careful observation during dynamic scanning may be required to differentiate the uni ed motion of gel mass from the membranous behaviour of a detached retina. If the vitreous contains pathological material this distinction is made easier. ! ! Describe the different types of retinal detachment. In this serious condition, your retina -- a thin layer of nerve tissue in the back of your!eye pulls away from its normal spot. Retinal detachments are divided into two main types:! 1. Rhegmatogenous (arising from a break in continuity)! 2. Non-rhegmatogeneous (secondary detachment)! • Two main forms of non-rhegmatogeneous detachment:! 1. Tractional ! 2. Exudative Mobility is less marked if the detachment is non rhegmatogeneous! ! Rhegmatogeneous Retinal Detachment: The most common type Retinal breaks which result in retinal detachment are caused by underlying weakness in the peripheral retina, from predisposing degeneration and vitreoretinal traction from a detached vitreous. Hole, tear or break in the retina allows vitreous gel (fluid from the middle of the eye) to leak underneath the retina. Once the liquid settles, the retina pulls away from the layer beneath it. Posterior vitreous detachment (PVD) is a common cause of retinal tears. This is a normal part of ageing that causes the vitreous gel to pull away from the retina in places. Usually harmless and often has no symptoms, but sometimes, the gel builds up so much and pulls so hard that it tears the retina. ! ! Non-Rhegmatogeneous Retinal Detachment: In this condition there is no retinal break and the detachment is tractional or exudative. ! ! Tractional Retinal Detachment:

- Occurs when scar tissue or other tissue grows on the retina and pulls it away from the layer underneath.

- Can lead to serious vision loss. - Often found in people with diabetes who have severe diabetic retinopathy, or damage to blood vessels in the retina.

- Contracting vitreoretinal membranes pull the sensory retinal away from the pigment epithelium, resulting in angular immobile detachments on dynamic scanning.

- Retinopathy and penetrating ocular trauma are the main causes. ! ! Retinopathy = retinal blood vessels leak fluid or bleed. ! ! Exudative Retinal Detachment:

- Rare. - Occurs when fluid collects under your retina, but there's no tear. It can affect both eyes. - This type of detachment is often comes from an eye injury or as a complication of a wide range of diseases. They include various inflammatory and!kidney diseases, as well as lyme disease, eye tumours, and severe high blood pressure. - Subretinal fluid (SRF) from the choroid enters the sub retinal space through damaged pigment epithelium caused by inflammation or tumour. - Under the influence of gravity, distribution of sub retinal fluid changes with alterations in eye position. - Dynamic scanning shows some mobility of the retina and usually an associated anterior choroidal detachment. !

- Retinal tears are small and cannot usually be identified by ultrasound. Occasionally, a flap of torn retina may be seen protruding into the vitreous cavity.! ! What are the ultrasonic appearances of a total retinal detachment?

- Classic total detachment shows a funnel shaped appearance!

! What are the ultrasonic appearances of a localised (or focal) retinal detachment? ! NEED TO COMPLETE! ! Outline the role of ultrasound in the evaluation of eye trauma.! How can you distinguish a choroidal detachment from a retinal detachment? !

! How can you distinguish a posterior vitreous haemorrhage from a retinal detachment? ! RD can be slightly more echogenic than PVD. However, the key to differentiating between the two is to identify the optic nerve first. RDs will remain attached to the optic nerve sheath, whereas PVDs will cross over the midline, hence, also crossing over the optic nerve. RD is not so mobile with eye movements, unlike PVD, which is very mobile with eye movements. Generally, RD has same thickness throughout, unlike PVD, which has varying degrees of thickness.! ! Vitreous hemorrhages (VH) and posterior vitreous detachments (PVD) will be apparent as the gain is increased. In contrast to RD, a PVD takes on a “swaying seaweed” appearance. It is seen as a thin, linear structure, which is not tethered to the optic disc. As the patient moves her eye, the linear flap will float back and forth, cross the optic nerve and will not be tethered to the back wall.! ! VHs will be seen as diffuse mobile opacities on high gain, taking on a “snow globe” appearance. Commonly seen in diabetics or after a concurrent PVD, patients commonly present with floaters.!!

! Describe the role of colour and spectral Doppler in the diagnosis of retinal detachment.

- Colour doppler helps differentiate between retinal detachment (showing blood flow) and the posterior surface of the detached gel (showing no blood flow). !

! Describe the scan appearances of a foreign body in the eye.

- Small penetrating bodies, e.g. metal or glass fragments travelling at high speed can cause penetrating injuries with the object retained within the globe.

- Most foreign bodies are detachable with ultrasound, however if made of soft material e.g. wood or organic matter, identification may be difficult, particularly if surrounded by haemorrhage.

- Hard materials such as metal, glass or stone are highly reflective. - Following penetration by a foreign body a track of haemorrhage may be seen crossing the vitreous, outlining the trajectory of the object and indicating its position.

- Small spheres of intragel gas show as highly reflective spots which may be confused with foreign bodies, however foreign bodies are usually more reflective with clear acoustic shadowing.

- Gas bubbles also move or rise with eye movements. - As some foreign bodies can be missed with ultrasound, it is important to use plain radiography or CT however ultrasound is superior for the detection of associated intraocular abnormalities. !

! What is the role of eye ultrasound in the management of the diabetic patient?

- In order to reduce the risk of diabetic eye disease (both retinopathy and maculopathy) progressing and causing visual loss, it is important for all people with diabetes to maintain good overall health and good control over their diabetes. This is especially important for patients who already have diabetic retinopathy (DR) which is already affecting their vision, or is likely to damage it soon. - About 5% of those with diabetes are affected by proliferative diabetic retinopathy, but in juvenile-onset diabetes the risk is increased to about 60% incidence after 30 years. - As retinopathy and penetrating ocular trauma are the two most common causes of Traction retinal detachment it is important that the diabetic patient is managed. ! ! What is the role of eye ultrasound in the management of a patient with a malignant melanoma of the retina? - Retinoblastoma is the commonest primary malignant intraocular tumour of childhood and comprises about 30% of all ocular tumours. - Rare - Retinoblastomas normally present at a late stage with leukocoria or ‘amaurotic cat’s eye’ however with the use of ultrasound to manage those who are at high risk of developing the condition, earlier stages can be seen if the funds is being kept under observation in these high risk patients. - This further increases prognosis and potential survival rate of the patient....