Evisceration

The dishevelled and disorganised contents of the eye are submitted in formalin fixative. If possible they should be examined grossly and, if recognisable, sorted into component parts. Calcified material (lens or remnants of osseous metaplasia in a phthisical eye) should be identified and processed via acid to avoid damage to microtome blades.

When examining the contents of the eye it is difficult to give a comprehensive account to validate the clinical history of the eye, and one is often reduced to noting the degree and type of the inflammatory process and, in the case of acute inflammation and pus, the presence of and type of organisms. Rarely is this procedure used to treat a tumour.

Enucleation External Anatomy

It is necessary to confirm that the specimen is indeed the right or left eye as given on the histopathology request form. This is done by orientating the eye using the positions of the rectus muscle, tendons and the superior and inferior oblique extra-ocular muscles. The superior oblique muscle has a long string-like tendon inserting into the sclera lateral and slightly posterior to the superior rectus muscle and superior to the optic nerve. The inferior oblique muscle is fleshy and brown right up to the insertion into the globe and is situated lateral and inferior to the optic nerve. So the eyes should have the superior oblique muscle, optic nerve and inferior oblique muscles forming a triangle when viewed posteriorly (Figure 20.3).

Having orientated the eye, a systematic list of the external features is made. The normal diameter is 23-24 mm. Conditions such as glaucoma may thin the sclera causing herniations or staphylomata in areas of weakness. Otherwise there may be a slight increase in diameter as may also be seen in myopia. Examination of the cornea includes noting any surgical or traumatic incisions, sutures, opacities or pigmentation. Is the iris visible? Is it symmetrical, abnormally pigmented or deficient? If it is deficient, where on a clock face (12 o'clock = superior) and what size? Is there pus or proteinaceous fluid in the anterior chamber?

The conjunctiva and sclera are examined for abnormal pigment, incisions, or evidence of radiotherapy plaques or bands for the treatment of detached retina.

Superior rectus

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Superior rectus

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Lateral rectus

Inferior rectus

Left eye

Right eye

Figure 20.3. Anatomical orientation of the eye. Landmarks on the eyes as viewed from the posterior aspect.

Inferior rectus

Inferior oblique

Superior oblique

Lateral rectus

Left eye

Right eye

Figure 20.3. Anatomical orientation of the eye. Landmarks on the eyes as viewed from the posterior aspect.

The optic nerve and scleral vessels are examined for evidence of tumour. After making these gross observations, it is advisable to photograph the external surfaces of the eye.

Laboratory Details

Fixation of the eye: Globes are usually fixed in formalin fixative. Prior to cutting, they are transferred to 95% alcohol as this "hardens" the sclera making it slightly easier to cut and improves the colour and presentation of the eye prior to photography.

Tools required: The best instrument to cut a globe is a long, very sharp thin blade. The idea is to get one long smooth cut that cuts the whole of the eye, rather than a series of sawing movements that disrupt the internal anatomy and make processing and sectioning difficult. A disposable microtome blade (10-15 cm) may be used but extreme care has to be taken to avoid spilling an innocent person's blood over the specimen.

Eyes opened and found to contain bone or calcified debris are gently decalcified in acid before finishing off the cutting. Eyes containing foreign bodies should have them removed carefully after noting and photographing their location.

Trans-illumination in eyes containing tumour: It may be possible to trans-illuminate the eye using a strong, narrow beam of light (usually fibre optic) in order to locate the mass. This is helpful in deciding how to cut and open the eye in order to have the classical section of central cornea, centre of pupil, lens, lesion and optic nerve.

Similarly, X-ray examination for bone or foreign bodies may be undertaken using needles on the external surface to help locate the lesion.

Techniques: (Figure 20.4) A thin section of the optic nerve is taken first and submitted for histology.

Vertical cuts to give calottes is the technique used when studying surgical lens extractions and the surgical site following a failure of or complications of cataract surgery. An implanted plastic lens may interfere with the smooth cutting of the blade and therefore should be anticipated.

Horizontal cuts give calottes which include cornea, centre of pupil, lens, lesion, macula and optic nerve. The inferior oblique helps one identify the posterior temporal sclera.

The calottes should be cut first 1 mm from the optic nerve proceeding anteriorly to cut the cornea about 2 mm medial to the limbus. The globe is placed on the cutting block and the

Figure 20.4. Blocking an eye specimen.

procedure repeated on the other side of the optic nerve. Vertical cutting results in a nasal calotte, a central wedge-shaped block and a temporal calotte. These can be further examined under liquid to conserve the anatomy, keeping the retina in situ. All blocks are examined, carefully noting

• the depth and contents of the anterior chamber.

• the presence or absence of the lens.

• the presence or absence of cataract, the vitreous (clear, gelatinous or turbid, the presence or absence of membranes).

• the retina, whether it is in situ or detached (a subretinal exudate indicates a true as opposed to artefactual retinal detachment).

• the presence or absence of recent/old haemorrhage in the vitreous or choroid.

• the thickness of the sclera.

Pathological Conditions

Tumours: There are two main tumours affecting the eye, malignant melanoma (presents from second decade to very elderly) and retinoblastoma (which presents in childhood). However, many other tumours have been described within the eye including adenomas and adenocarcinomas of the ciliary body epithelium, schwannomas, lymphomas, haemangiomas and metastatic tumours from lung, breast and stomach.

Malignant melanomas may occur anywhere in the uveal tract but are most commonly found in the choroid. They arise in the choroid, pushing Bruch's membrane over them until they perforate it causing the overlying retina to detach with consequent formation of a subretinal exudate. The tumour gains access to the venous side of the systemic circulation via the perforations of the sclera by the artery, vein and nerve bundles and may be seen causing black pigmentation in the region of the vortex veins. Alternatively, malignant melanomas may infiltrate the filtration angle of the anterior chamber en route to Schlemm's canal and the conjunctival veins. This causes abnormal pigmentation of the conjunctiva at the limbus. Uveal malignant melanoma classically metastasises to the liver.

Prognosis for these tumours depends on three major factors

1. Age at presentation: older is worse than young.

2. Site within the eye: posterior is better than equatorial, which is better than anterior where it quickly gains access to the venous side of the systemic circulation via Schlemm's canal.

3. Size of tumour (maximum diameter):

- 15 mm poor prognosis,

- 10 mm guarded prognosis,

- 5 mm interesting, but not immediately lethal.

The size of tumour covers factors such as cell type, as small tumours tend to be spindle B cell type and the larger tumours have increasing numbers of epithelioid cells. Similarly, larger tumours tend to be exiting the eye via the sclera or Schlemm's canal.

TNM classification of tumour spread ciliary body and choroid malignant melanoma.

pT1 tumour < 10 mm maximum diameter, < 2.5 mm height*.

pT2 tumour > 10 to 16 mm maximum diameter, > 2.5 to 10 mm height*.

* a no extraocular extension.

b microscopic extraocular extension. c gross extraocular extension. pT3 tumour > 16 mm maximum diameter and/or 10 mm height. pT4 pT3 with extraocular extension. pN1 regional lymph node metastasis.

Retinoblastoma - two types:

1. Congenital: where both eyes ± the pineal gland are affected.

2. Sporadic: where one eye is affected and the patient carries a genetic risk for the next generation.

The tumour arises in one, two or all three of the layers of the retina forming retinoblasts which may infiltrate the overlying vitreous (endophytic) or the underlying subretinal space (exophytic). The tumour exits the eye via the optic nerve to the brain. It infiltrates the choroid if there has been damage to Bruch's membrane (usually following X-radiation treatment). From there it may metastasise systemically.

Treatment of congenital retinoblastoma usually involves excising the worse eye and treating the better eye with collumated irradiation, hoping to conserve some function. For sporadic cases the affected eye is removed, hoping to avoid spread to the brain via the optic nerve.

TNM classification of tumour spread retinoblastoma pT1 tumour confined to the retina, vitreous or subretinal space.

pT2 minimal invasion of optic nerve (not through lamina cribrosa) and choroid.

pT3 significant invasion of optic nerve (through lamina cribrosa but not to resection line)

and choroid. pT4 extraocular invasion. pN1 regional lymph node metastasis.

Glaucoma: The main cause for enucleation is the painful blind eye. Such eyes usually have a long history of attending an ophthalmologist with episodes of therapy (medical and surgical) before opting for pain relief and pre-emptively preventing the eye from rupturing due to the increased intra-ocular pressure causing thinning and anaesthesia of the cornea.

Such eyes are cut and processed with attention to the clinical history in order to corroborate the clinical findings and demonstrate the cause of the open or closed angle glaucoma.

Inflammation: The eye is subject to endophthalmitis secondary to penetrating injuries or surgical procedures. This may be treated by steroids provided it is not infected. Infections - bacterial, fungal, helminthic (toxocariasis) and protozoal (toxoplasmosis) - cause a spectrum of acute to chronic inflammation. The presence of pus and the potential of infection to track to the CNS may necessitate evisceration or enucleation. Often the inflammation subsides but the resultant healing process precipitates detachment of the retina and glaucoma requiring enucleation of a painful blind eye.

Granulomatous inflammation affecting the choroid or sclera may be the result of sympathetic endophthalmitis, sarcoidosis, rheumatoid arthritis, Wegener's granulomatosis and the terminal stages of miliary TB.

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