Ординатура / Офтальмология / Английские материалы / Comprehensive Ophthalmology_Khurana_2007

The operation using glaucoma valve implant is also known as Seton operation.

Glaucoma valve implants commonly used include Molteno (Fig. 9.25) Krupin-Denver and AGV. Indications of artificial drainage shunts include :

Neovascular glaucoma;

Glaucoma with aniridia; and

Intractable cases of primary and secondary glaucoma where even trabeculectomy with adjunct antimetabolite therapy fails.

CYCLO-DESTRUCTIVE PROCEDURES

Cyclo-destructive procedures lower IOP by destroying part of the secretory ciliary epithelium thereby reducing aqueous secretion.

Indications. These procedure are used mainly in absolute glaucomas.

Cyclo-destructive procedures in current use are:

1.Cyclocryotherapy (most frequent),

2.Nd: Yag laser cyclodestruction, and

3.Diode laser cyclophotocoagulation.

Fig. 9.25. Artificial drainage shunt operation using Molteno implant.

Technique of cyclocryopexy

1.Anaesthesia. Topical and peribulbar block anaesthesia is given.

2.Lids separation is done with eye speculum.

3.Cryoapplications. Cryo is applied with a retinal probe placed 3 mm from the limbus. A freezing at

–80oC for 1 minute is done in an area of 180° of the globe (Fig. 9.26).

If ineffective, the procedure may be repeated in the same area after 3 weeks. If still ineffective, then the remaining 180° should be treated.

Mechanism. IOP is lowered due to destruction of the secretory ciliary epithelium. The cells are destroyed by intracellular freezing.

Fig. 9.26. Site of cyclocryopexy.

APPLIED ANATOMY

Vitreous humour is an inert, transparent, jelly-like structure that fills the posterior four-fifth of the cavity of eyeball and is about 4 ml in volume. It is a hydrophilic gel that mainly serves the optical functions. In addition, it mechanically stabilizes the volume of the globe and is a pathway for nutrients to reach the lens and retina.

Structure. The normal youthful vitreous gel is composed of a network of randomly-oriented collagen fibrils interspersed with numerous spheroidal macromolecules of hyaluronic acid. The collapse of this structure with age or otherwise leads to conversion of the gel into sol. The vitreous body can be divided into two parts: the cortex and the nucleus (the main vitreous body) (Fig. 10.1).

1. Cortical vitreous. It lies adjacent to the retina posteriorly and lens, ciliary body and zonules anteriorly. The density of collagen fibrils is greater in this peripheral part. The condensation of these fibrils form a false anatomic membrane which is called as anterior hyaloid membrane anterior to ora serrata and posterior hyaloid membrane posterior to ora.

The attachment of the anterior hyaloid membrane to the posterior lens surface is firm in the young and weak in the elderly whereas posterior hyaloid membrane remains loosely attached to the internal limiting membrane of the retina throughout life. These membranes cannot be discerned in a normal eye unless the lens has been extracted and posterior vitreous detachment has occurred.

2. The main vitreous body (nucleus). It has a less dense fibrillar structure and is a true biological gel. It is here where liquefactions of the vitreous gel start first. Microscopically the vitreous body is homogenous, but exhibits wavy lines as of watered silk in the slit-lamp beams. Running down the centre of the vitreous body from the optic disc to the posterior pole of the lens is the hyaloid canal (Cloquet’s canal) of doubtful existence in adults. Down this canal ran the hyaloid artery of the foetus.

Attachments. The part of the vitreous about 4 mm across the ora serrata is called as vitreous base, where the attachment of the vitreous is strongest. The other firm attachments are around the margins of the optic disc, foveal region and back of the crystalline lens by hyloidocapsular ligament of Wieger.

DISORDERS OF THE VITREOUS

VITREOUS DETACHMENTS

1. Posterior vitreous detachment (PVD)

VITREOUS LIQUEFACTION (SYNCHYSIS)

Vitreous liquefaction (synchysis) is the most common degenerative change in the vitreous.

Causes of liquefaction include:

1.Degenerations such as senile, myopic, and that associated with retinitis pigmentosa.

2.Post-inflammatory, particularly following uveitis.

3.Trauma to the vitreous which may be mechanical (blunt as well as perforating).

4.Thermal effects on vitreous following diathermy, photocoagulation and cryocoagulation.

5.Radiation effects may also cause liquefaction. Clinical features. On slit-lamp biomicroscopy the vitreous liquefaction (synchysis) is characterised by absence of normal fine fibrillar structure and visible pockets of liquefaction associated with appearance of coarse aggregate material which moves freely in the free vitreous. Liquefaction is usually associated with collapse (synersis) and opacities in the vitreous which may be seen subjectively as black floaters in front of the eye.

It refers to the separation of the cortical vitreous from the retina anywhere posterior to vitreous base (3-4 mm wide area of attachment of vitreous to the ora serrata).

PVD with vitreous liquefaction (synchysis) and collapse (synersis) is of common occurrence in majority of the normal subjects above the age of 65 years (Fig. 10.2). It occurs in eyes with senile liquefaction, developing a hole in the posterior hyaloid membrane. The synchytic fluid collects between the posterior hyaloid membrane and the internal limiting membrane of the retina, and leads to PVD up to the base along with collapse of the remaining vitreous gel (synersis). These changes occur more frequently in the aphakics than the phakics and in the myopes than the emmetropes.

Clinical features. PVD may be associated with flashes of light and floaters. Biomicroscopic examination of the vitreous reveals a collapsed vitreous (synersis) behind the lens and an optically clear space between the detached posterior hyaloid phase and the retina.

Fig. 10.2. Posterior vitreous detachment with synchysis and synersis.

A ring-like opacity (Weiss ring or Fuchs ring), representing a ring of attachment of vitreous to the optic disc, is pathognomic of PVD.

Complications of PVD. These include retinal breaks, vitreous haemorrhage, retinal haemorrhages and cystoid maculopathy.

2.Detachment of the vitreous base and the anterior vitreous

It usually occurs following blunt trauma. It may be associated with vitreous haemorrhage, anterior retinal dialysis and dislocation of crystalline lens.

VITREOUS OPACITIES

Since vitreous is a transparent structure, any relatively non-transparent structure present in it will form an opacity and cause symptoms of floaters. Common conditions associated with vitreous opacities are described below.

Muscae volitantes. These are physiological opacities and represent the residues of primitive hyaloid vasculature. Patient perceives them as fine dots and filaments, which often drift in and out of the visual field, against a bright background (e.g., clear blue sky).

Persistent hyperplastic primary vitreous (PHPV) results from failure of the primary vitreous structure to regress combined with the hypoplasia of the posterior portion of vascular meshwork.

Clinically it is characterized by a white pupillary reflex (leucocoria) seen shortly after birth. Associated

anomalies include congenital cataract, glaucoma, long and extended ciliary processes, microphthalmos and vitreous haemorrhage.

Differential diagnosis needs to be made from other causes of leucocoria especially retinoblastoma, congenital cataract and retinopathy of prematurity. Computerised tomography (CT) scanning helps in diagnosis.

Treatment consists of pars plana lensectomy and excision of the membranes with anterior vitrectomy provided the diagnosis is made early. Visual prognosis is often poor.

Inflammatory vitreous opacities. These consist of exudates poured into the vitreous in patients with anterior uveitis (iridocyclitis), posterior uveitis (choroiditis), pars planitis, pan uveitis and endophthalmitis.

Vitreous aggregates and condensation with liquefaction. It is the commonest cause of vitreous opacities. Condensation of the collagen fibrillar network is a feature of the vitreous degeneration which may be senile, myopic, post-traumatic or postinflammatory in origin.

Amyloid degeneration. It is a rare condition in which amorphous amyloid material is deposited in the vitreous as a part of the generalised amyloidosis. These vitreous opacities are linear with footplate attachments to the retina and the posterior lens surface.

Asteroid hyalosis. It is characterised by small, white rounded bodies suspended in the vitreous gel. These are formed due to accumulation of calcium containing lipids. Asteroid hyalosis is a unilateral, asymptomatic condition usually seen in old patients with healthy vitreous. There is a genetic relationship between this condition, diabetes and hypercholesterolaemia. The genesis is unknown and there is no effective treatment.

Synchysis scintillans. In this condition, vitreous is laden with small white angular and crystalline bodies formed of cholesterol. It affects the damaged eyes which have suffered from trauma, vitreous haemorrhage or inflammatory disease in the past. In this condition vitreous is liquid and so, the crystals sink to the bottom, but are stirred up with every movement to settle down again with every pause. This phenomenon appears as a beautiful shower of golden rain on ophthalmoscopic examination. Since

the condition occurs in damaged eye, it may occur at any age. The condition is generally symptomless, but untreatable.

Red cell opacities. These are caused by small vitreous haemorrhages or leftouts of the massive vitreous haemorrhage.

Tumour cells opacities. These may be seen as freefloating opacities in some patients with retinoblastoma, and reticulum cell sarcoma.

VITREOUS HAEMORRHAGE

Vitreous haemorrhage usually occurs from the retinal vessels and may present as pre-retinal (sub-hyaloid) or an intragel haemorrhage. The intragel haemorrhage may involve anterior, middle, posterior or the whole vitreous body.

Causes

Causes of vitreous haemorrhage are as follows:

1.Spontaneous vitreous haemorrhage from retinal breaks especially those associated with PVD.

2.Trauma to eye, which may be blunt or perforating (with or without retained intraocular foreign body) in nature.

3.Inflammatory diseases such as erosion of the vessels in acute chorioretinitis and periphlebitis retinae primary or secondary to uveitis.

4.Vascular disorders e.g., hypertensive retinopathy, and central retinal vein occlusion.

5.Metabolic diseases such as diabetic retinopathy.

6.Blood dyscrasias e.g., retinopathy of anaemia, leukaemias, polycythemias and sickle-cell retinopathy.

7.Bleeding disorders e.g., purpura, haemophilia and scurvy.

8.Neoplasms. Vitreous haemorrhage may occur from rupture of vessels due to acute necrosis in tumours like retinoblastoma.

9.Idiopathic

Clinical features

Symptoms. Sudden development of floaters occurs when the vitreous haemorrhage is small. In massive vitreous haemorrhage, patient develops sudden painless loss of vision.

Signs

Distant direct ophthalmoscopy reveals black shadows against the red glow in small

haemorrhages and no red glow in a large haemorrhage.

Direct and indirect ophthalmoscopy may show presence of blood in the vitreous cavity.

Ultrasonography with B-scan is particularly helpful in diagnosing vitreous haemorrhage.

Fate of vitreous haemorrhage

1.Complete absorption may occur without organization and the vitreous becomes clear within 4-8 weeks.

2.Organization of haemorrhage with formation of a yellowish-white debris occurs in persistent or recurrent bleeding.

3.Complications like vitreous liquefaction, degeneration and khaki cell glaucoma (in aphakia) may occur.

4.Retinitis proliferans may occur which may be complicated by tractional retinal detachment.

Treatment

1.Conservative treatment consists of bed rest, elevation of patient’s head and bilateral eye patches. This will allow the blood to settle down.

2.Treatment of the cause. Once the blood settles down, indirect ophthalmoscopy should be performed to locate and further manage the causative lesion such as a retinal break, phlebitis, proliferative retinopathy, etc.

3.Vitrectomy by pars plana route should be considered to clear the vitreous, if the haemorrhage is not absorbed after 3 months.

VITREO-RETINAL DEGENERATIONS

See page 270.

VITRECTOMY

Surgical removal of the vitreous is now not an infrequently performed procedure.

TYPES

1.Anterior vitrectomy. It refers to removal of anterior part of the vitreous.

2.Core vitrectomy. It refers to removal of the central bulk of the vitreous. It is usually indicated in endophthalmitis.

3.Subtotal and total vitrectomy. In it almost whole of the vitreous is removed.

TECHNIQUES

Open-sky vitrectomy

This technique is employed to perform only anterior vitrectomy.

Indications

Vitreous loss during cataract extraction.

Aphakic keratoplasty.

Anterior chamber reconstruction after perforating trauma with vitreous loss.

Removal of subluxated and anteriorly dislocated lens.

Surgical technique. Open sky vitrectomy is performed through the primary wound to manage the disturbed vitreous during cataract surgery or aphakic keratoplasty. It should be performed using an automated vitrectomy machine. However, if the vitrectomy machine is not available, it can be performed with the help of a triangular cellulose sponge and de Wecker’s scissors (sponge vitrectomy).

Closed vitrectomy (Pars plana vitrectomy)

Pars plana approach is employed to perform core vitrectomy, subtotal and total vitrectomy.

Indications

Endophthalmitis with vitreous abscess.

Vitreous haemorrhage.

Proliferative retinopathies such as those associated with diabetes, Eales’ disease, retinopathy of prematurity and retinitis proliferans.

Complicated cases of retinal detachment such as those associated with giant retinal tears, retinal dialysis and massive vitreous traction.

Removal of intraocular foreign bodies.

Removal of dropped nucleus or intraocular lens from the vitreous cavity.

Persistent primary hyperplastic vitreous.

Vitreous membranes and bands.

Surgical techniques

Pars plana vitrectomy is a highly sophisticated microsurgery which can be performed by using two type of systems:

1. Full function system vitrectomy is now-a-days sparingly used. It employs a multifunction system that comprises vitreous infusion, suction, cutter and illumination (VISC), all in one.

2. Divided system approach is the most commonly employed technique in modern vitrectomy. In this technique three separate incisions are given in pars plana region. That is why the procedure is also called three-port pars plana vitrectomy. The cutting and aspiration functions are contained in one probe, illumination is provided by a separate fiberoptic probe and infusion is provided by a cannula introduced through the third pars plana incision (Fig. 10.3).

Fig. 10.3. Three-port pars plana vitrectomy using divided system approach

Advantages of divided system approach include smaller instruments, easy handling, improved visualization, use of bimanual technique and adequate infusion by separate cannula.

VITREOUS SUBSTITUTES

Vitreous substitutes or the so called temponading agents are used in vitreo-retinal surgery to:

Restore intraocular pressure and

Provide intraocular tamponade

An ideal vitreous substitute should be:

Having a high surface tension,

Optically clear, and

Biologically inert.

Currently used vitreous substitutes in the absence of an ideal substitute are:

1.Air is commonly used internal temponade in uncomplicated cases. It is absorbed within 3 days.

2.Physiological solutions such as Ringer’s lactate or balanced salt solution (BSS) can be used as substitute after vitrectomy for endophthalmitis or uncomplicated vitreous haemorrhage.

3.Expanding gases are preferred over air in complex cases requiring prolonged intraocular temponade. They are used as 40% mixture with air examples are:

Sulphur hexafluoride (SF6). It doubles its volume and lasts for 10 days.

Perfluoropropane. It quadruples its volume and lasts for 28 days.

4.Perflurocarbon liquids (PFCL) are heavy liquids which are mainly used:

To remove dropped nucleus or IOL from the vitreous cavity,

To unfold a giant retinal tear, and

To stabilize the posterior retina during peeling of the epiretinal memebrane.

5.Silicone oils allow more controlled retinal manipulation during operation and can be used for prolonged intraocular temponade after retinal detachment surgery.

APPLIED ANATOMY

Retina, the innermost tunic of the eyeball, is a thin, delicate and transparent membrane. It is the most highly-developed tissue of the eye. It appears purplish-red due to the visual purple of the rods and underlying vascular choroid.

Gross anatomy

Retina extends from the optic disc to the ora serrata. Grossly it is divided into two distinct regions: posterior pole and peripheral retina separated by the so called retinal equator.

Retinal equator is an imaginary line which is considered to lie in line with the exit of the four vena verticose.

Posterior pole refers to the area of the retina posterior to the retinal equator. The posterior pole of the retina includes two distinct areas: the optic disc and macula lutea (Fig. 11.1). Posterior pole of the retina is best examined by slit-lamp indirect biomicroscopy using +78D and +90D lens and direct ophthalmoscopy.

Optic disc. It is a pink coloured, well-defined circular area of 1.5-mm diameter.At the optic disc all the retinal

layers terminate except the nerve fibres, which pass through the lamina cribrosa to run into the optic nerve. A depression seen in the disc is called the physiological cup. The central retinal artery and vein emerge through the centre of this cup.

Macula lutea. It is also called the yellow spot. It is comparatively deeper red than the surrounding fundus and is situated at the posterior pole temporal to the optic disc. It is about 5.5 mm in diameter. Fovea centralis is the central depressed part of the macula. It is about 1.5 mm in diameter and is the most sensitive part of the retina. In its centre is a shining pit called foveola (0.35-mm diameter) which is situated about 2 disc diameters (3 mm) away from the temporal margin of the disc and about 1 mm below the horizontal meridian.An area about 0.8 mm in diameter (including foveola and some surrounding area) does not contain any retinal capillaries and is called foveal avascular zone (FAZ). Surrounding the fovea are the parafoveal and perifoveal areas.

Peripheral retina refers to the area bounded posteriorly by the retinal equator and anteriorly by the ora serrata. Peripheral retina is best examined with indirect ophthalmoscopy and by the use of Goldman three mirror contact lens.