Ординатура / Офтальмология / Английские материалы / Pediatric Opthalmology_Mukherjee_2005

2.Acid mucopolysaccharides form biological glue between the photo receptors and the RPE.

The other contributory factors are:

1.Presence of semisolid vitreous on the retina, which exerts a force to keep the two layers in apposition.

2.Almost lack of mobility of normal vitreous.

3.Normal intra ocular tension.

The factors other than apposed layers of retina that keep this space devoid of fluid are:

1.Active metabolic transport between retinal pigment epithelium and sub retinal fluid

2.Oncotic pressure gradient between sub retinal space and choroid also keep the space free of fluid.

The vitreous plays an important role in keeping the retina apposed. So long the vitreous is semi-solid and it does not exert any traction on retina even at places where it is attached i.e. the ora serrata, round the optic nerve, at the fovea and along the major blood vessels. Abnormal vitreo retinal attachments develop over chorio retinal scar.

Retinal detachment has been divided into two groups:

1.Rhegmatogenous

2.Non rhegmatogenous (a) Tractional

(b) Exudative

Rhegmatogenous retinal detachment is most common detachment in children followed by traction. Exudative retinal detachment is least common in children.

Rhegmatogenous retinal detachment is a treatable cause of diminished vision and party preventable.

The two factors that contribute to the development of rhegmatogenous detachment are:

1.Retinal break (a) Hole.

(b) Tear

2.Liquifaction of vitreous

Presence of only one of the above rarely leads to retinal detachment.

Retinal breaks

These are full thickness passages between the vitreous cavity and space between RPE and sensory retina. Retinal breaks may take different shapes with varied size and number. One thing common about retinal breaks is that they predispose retinal detachment.61 The retinal breaks look dark red because the retinal pigment epithelium is exposed. About six percent of eyes have retinal holes without retinal detachment. It develops only in one in seventy such cases62. The circular breaks are called holes while others are called tears. All Retinal breaks

are almost exclusively seen on the retinal periphery except a macular hole or a traumatic tear. Macular holes, generally do not lead to detach-ment. Macular holes can be full thickness or partial. Macular holes are rare in children.

Round holes

These are punched out circular holes, size of which vary from pin head to almost as large as the optic disc. There number also vary from single to multiple. When a piece of retina is hinged to one edge of the hole or attached the retracted vitreous near the hole and protrudes in the vitreous, it is called operculated hole. Most of the holes are non operculated, the round holes develop in the area of chorio retinitis or in lattice degeneration. The non operculated holes are also known as atrophic holes. They have low incidence of detachment.

Tears according to their shape are called - Horse shoe shaped; giant tear and dialysis.

The horse shoe holes—These are crescent shaped tear with concavity towards the periphery. The tongue of the retina towards the tear is called the flap. Sometimes bands arising from the vitreous may be attached to the apex of the flap. They are common in children. They are never as numerous as round holes.

Giant tears

These are also called limbus parallel tears due to their orientation in relation to limbus. They are slightly posterior to ora serrata and parallel to it. These are the largest tears, generally there is only one giant tear in one eye. The tear extends more than 90° along the circumference, it may rarely extend all round. They are seen in younger patients. In about 80% of giant tears, no predisposing factor is detected. It is common in blunt injury, they can be bilateral and have poor prognosis.

Dialysis of retina

This is disinsertion of retina at the ora serrata. Commonest site is inferio temporal quadrant, which is most stretched and least developed. Commonest cause is trauma otherwise it can be idiopathic in some cases, they are bilateral. The detachment progresses slowly, as the progression is slow, macular involvement is not felt abruptly. They are more common in young males.

Liquefaction of vitreous

Normal vitreous is a semisolid gel incapable to flow. The vitreous does not have a formed capsule, still it keeps its shape in the vitreous cavity. It is only liquified vitreous that causes retinal detachment but not unless it has come out of the vitreous cortex. The fluid vitreous when associated with deficiency in the vitreous body flows in between the vitreous body and the retina and fill the newly formed retro hyaloid space. This pushes the vitreous forwards and the condition is called posterior vitreous detachment (P.V.D.). Following PVD the retina looses its support from a stable vitreous. The retina is directly affected by traction of vitreous. The traction may be normal anatomical adhesion or pathological chorio retinal scar.

In adults the liquefaction of the vitreous is an ageing process and called synchisis senilis. This does not happen in children. In children the vitreous is liquified following trauma

more in penetrating injury than blunt injury, chronic inflamation of choroid and retina, retained intra ocular foreign bodies and myopia.

In the next stage the fluid vitreous finds its way into the potential space in between the sensory retina and the retinal pigment epithelium and distends the space resulting into a retinal separation or rhegmatogenous detachment. The sub retinal fluid gravitates down to most dependent part and due to this it separates more retinal area from its natural apposition. Hence a hole at 12 o’clock is likely to cause more extensive detachment on either side of the hole while a relatively large rent at six o’clock detaches smaller area and the progression is slow.

Symptoms

1.A shallow detachment at the lower part away from the macula may be symptomless.

2.Two common symptoms of rhegmatogenous retinal detachment are-

•Photopsia (Flashes of light) due to retinal irritation and floaters. The floaters may be due to RBC from the torn blood vessel at the site of tear, or due to liquified vitreous. A ring shaped shadow the Weiss ring denotes posterior vitreous detachment, occasionally a cobweb like opacity may be seen due to condensation of collagen fibres in collapsed vitreous.

3.Metamorphopsia develops in early stages of detachment due to unevenness of the retinal surface.

4.Diminished vision—Degree of loss of vision depends on macular involvement. In large detachment with a superior hole, loss of vision may be acute, it may fall from 6/ 6 to hand movement of less.

The causes of diminished vision in retinal detachment are:

1.Involvement of macula

2.Overhanging detachment in front of macula

3.Blood in front of macula

In large detachment there may be associated loss of projection in the corresponding quadrant.

5.Field changes—The field defects start from the periphery and spread towards the centre. The field defect is brought about by spread of sub retinal fluid behind the equator. The patient perceives the field loss as either a shadow, approaching from the side, or a curtain coming down from above. Lower field defect is generally felt earlier than upper field loss.

Signs of retinal detachment are variable. They depend upon site of the detachment, extent of the detachment, duration of detachment.

1.Uncorrectable diminished vision—This may be associated with faulty projection when elicited by small pinpoint light source.

2.Externally the eye is non congested and non tender.

3.Pupil—In case of large retinal detachment the pupil may show Marcus Gunn pupil. In small detachments the pupillary reaction may be normal.

4.Intra ocular tension is lower by 5-6 mm than previously noted IOP.

5.Anterior chamber reaction is common in long standing detachment, may occasionally be present in recent cases.

6.Retinoscopy

(a) In case of extensive retinal detachment the retinal glow may be absent.

(b) Retinal detachment in the posterior pole may give a grey reflex due to pallor of the detached retina.

(c) Hypermetropic shift of refractive error i.e. the pre existing myopic refraction is lessened and hypermetropia increased.

7.Fundus examination—The clue to diagnosis is in ophthalmoscopic examination of the fundus under maximum mydriasis by indirect ophthalmoscopy, preferably by scleral indentation.

Direct ophthalmoscopy may be sufficient to diagnose presence of retinal detachment. It fails to pinpoint the cause i.e. the break, its position, number and size.

(i) With direct ophthalmoscope, the detached retina is slightly opaque due to loss of underlying choroidal pattern. The grey surface is convex. The surface in corrugated due to intra retinal edema. The retinal vessels both arteries and veins look darker than in undetached retina. The colour difference between the arteries and veins is less marked. The detached retina may undulate with movement of the eye with out shifting in the fluid. The sub retinal fluid may extend up to the ora serrata. The above findings are better appreciated by indirect ophthalmoscope as it has stereopsis and larger field.

(ii) The retinal breaks—The presence of retinal break is the most important sign in rhegmatogenous retinal detachment, both as a diagnostic as well as prognostic feature and mode of treatment to be undertaken. The breaks are generally on the periphery, may vary from solitary hole to multiple holes and breaks. There may be very small or may present as large dialysis.

(iii) Vitreous—Vitreous may show large floaters. Posterior vitreous detachment is almost always present. In detachment of recent origin, blood may be present in the subhyaloid space or in the liquefied vitreous. The anterior vitreous may have tobacco dusting. The vitreous may be attached to the operaculum of a hole or flap of a tear.

(iv) The periphery besides break may show peripheral degeneration especiallylattice degeneration or patches of chorio retinal scar.

The fundus finding of long standing retinal detachment differ considerably from that of recent detachment. They are :

1.High-water mark if the retinal detachment is about a month old, pigments are deposited at the border of the detachment which gradually fade. They do not represent edge of sub retinal fluid. They lag behind the edge of sub retinal fluid.

2.Retinal thinning - This looks like retinoschisis.

3.Sub retinal fibrosis- Opaque strands develop on the detached retina.

4.Intra retinal cysts - If retina remains detached for more than one year, intra retinal cyst may develop that disappear with re attachment of retina.

Other investigation that may be required

1.Ultrasonography is indicated in opaque media.

2.Slit lamp biomicroscopy may be required but does not have much advantage over indirect ophthalmoscope.

Predisposing factors

1.Males are more predisposed to retinal detachment.

2.Family history—Retinal detachment can be seen in siblings or parents.

3.Myopia—It is a well known factor that incidence of rhegmatogenous retinal detachment is more in myopia. Incidence of detachment increases with increase in degree of myopia. It is more common in high myopia but low and moderate myopes are not immune. Incidence of rhegmatogenous retinal detachment is higher in myopicaphakics and myopicpseudophakics. Blunt trauma may precipitate detachment more frequently in myopia than in non myopic. Myopic males are more prone to detachment than females. Myopes are more likely to have bilateral retinal detachment.

The causes of higher incidence of retinal detachment in myopia are many and may work in combination, they are:

(i) The apposition of sensory retina to pigment epithelium is poorer.

(ii) Myopes suffer from lattice degeneration more commonly than non myopes.

(iii) Myopic retina is more stretched than non myopic retina, hence thin and likely to develop tears.

(iv) A genetic factor may also be a predisposing cause.

4.Trauma—Both blunt as well as penetrating injury can cause retinal detachment. Blunt trauma causes more detachment than open globe injury. Most of the time the tear develops at the time of original injury. Any type of break is possible, holes are less common. Out of all tears retinal dialysis is more common that progresses slowly. Liquifaction of vitreous is common following blunt injury so is posterior vitreous detachment.

5.Aphakia

(a) Aphakia following intra capsular lens extraction used to be a major cause of senile retinal detachment prior to IOL surgery became popular. However intra capsular lens extraction was never a cause of aphakic detachment in children in whom this surgery was not performed. Traumatic aphakia remains a cause of retinal detachment in children. Spontaneous dislocation of lens in Marfan’s syndrome is also associated with rhegmatogenous retinal detachment.

(b) Detachment following extra capsular lens extraction is less common than intra capsular lens extraction but never free from it. The incidence increases if repeated needling are performed.

(c) Pseudophakia is not a guarantee against rhegmatogenous retinal detachment. The incidence is higher in children because incidence of PCO is very in high in children that require laser capsulotomy which itself is a cause of retinal detachment.

6.Congenital anomalies - Choroidal coloboma, persistent hyperplastic primary vitreous, congenital pit of the optic nerve head are some of the congenital anomalies that predispose rhegmatogenous retinal detachment.

7.Syndromes associated with rhegmatogenous detachment are - Marfan’s, Ehler Danlos, Wagner, Pierre-Robinson, Stickler syndrome are frequently associated with rhegmatogenous detachment.

Untreated rhegmatogenous retinal detachment may follow any of the following course

1.A small detachment especially with superior hole rapidly expands and may become total.

2.Many a times, lower detachment may not progress and remain so due to formation of line of demarcation. Such detachment can have good anatomical apposition following surgery but visual prognosis is guarded.

3.Small localised detachment have been reported to get reattached over prolonged bed rest only to recur following strain.

4.Most of the untreated detachments develop complicated contract, chronic uveitis, hypotony, rarely phthisis that may terminate in blindness.

Differential diagnosis of rhegmatogenous retinal detachment

Differential diagnosis consist of two types of disease:

1.Where there is actual retinal detachment, these comprise of non rhegmatogenous retinal detachments

(i) Tractional retinal detachment (ii)Exudative retinal detachment

2 Those condition that mimic retinal detachment (i) Congenital and juvenile retinoschisis

(ii) Choroidal detachment (iii) Cilio choroidal detachment (iv) Vitreous bands.

(v) Dislocated lens. (vi) Parasitic cysts

Non rhegmatogenous retinal detachment

Non rhegmatogenous retinal detachment may it be tractional or exudative have following common features:

1.They do not have breaks in retina as a primary cause of detachment. Exudative detachment never develops a break. A tractional detachment can develop a hole due to abnormal traction on the retina.

2.The detachment surface does not have corrugation.

3.The sub retinal fluid is not a liquefied vitreous.

4.There is no hyaluronic acid in sub retinal fluid.

Tractional retinal detachment

Common cause of tractional retinal detachment in adults are - Proliferative diabetic retinopathy, Eale’s disease, cataract extraction with incarcerated vitreous. These conditions are not seen in children.

The common causes of tractional retinal detachment in children are:

1.Persistent hyper plastic primary vitreous

2.Retinopathy of prematurity

3.Hemoglobinopathy

4.Parsplanitis

5.Intra ocular foreign body

6.Congenital toxoplasmosis

7.Penetrating injury

The tractional retinal detachments develop slowly, many a times the primary cause like injury may overshadow and a child may not complain of symptoms especially in unilateral cases.

On examination

There is no break. The detachment has scalloped border. It does not reach the ora except in parsplanitis, the surface is concave, and the detached retina is peaked at the site of the traction. There is no movement of sub retinal fluid. The elevation is moderate. If breaks develop due to pull of the traction, already existing detachment becomes worse and behaves like a rhegmatogenous detachment, fluorescein angiography does not contribute much in diagnosis. There is no leaking or pooling of dye, occasionally there may be some window defect.

Treatment is directed towards reduction of tractional force either by denting the sclera in by way of scleral buckle, scleral resection or scleral encircling band or cutting the traction band. In most of the cases both are required.

Exadative retinal detachment

The incidence of exudative detachment is for less than rhegmatogenous and tractional detachment in children.

The common causes of exudative retinal detachment are:

Angiomatosis retinae, Coat’s disease, retinoblastoma, peripheral uveitis, dysproteinemias, choroidal rupture.

The characteristics of an exudative retinal detachment are—The surface is convex, the boundaries are convex, neither retinal breaks or traction bands are present. The border does not reach the ora. The sub retinal fluid shifts. The elevation of detached retina is moderate, on fluorescein angiography the sub retinal fluid is tinged by the dye but there is no leak. There is always evidence of primary disease. The condition waxes and wanes, may either spontaneously disappear or retina gets attached with treatment of primary cause. Ultrasonography may show a sub retinal growth, generally a tumour. In case of sub retinal tumour the retina is stretched over the tumour with exudate round the tumour. There may be a tuft of blood vessel on the retinal highest spot of elevation. Such elevations in the past were referred to as solid detachment.

Management of rhegmatogenous retinal treatment

There is no medical treatment for rhegmatogenous retinal detachment, prolonged bed rest in particular position, prolonged patching of two eyes, use of pinholes and stenopic slits all have proved to be futile.

Prophylaxis

All children with family history of rhegmatogenous retinal detachment, especially if they have myopia and all children who have sustained closed or open globe injury with history of floaters and photopsia, should be examined by indirect ophthalmoscope with scleral indentation. The examination should be repeated every six month for next few years and if a hole or tear is found, it should be closed adequately by laser or cryo. Some of them may be large enough to be closed by local scleral explant.

Some of the points to remember are:

1.A tear is more likely to produce retinal detachment than a hole in the same location.

2.Larger breaks produce more detachment than smaller but size of break is not always proportionate to its ability to produce detachment.

3.Superior breaks produce early and more extensive detachment.

4.Lower breaks produce less and shallow detachment.

5.Breaks behind the ora are more likely to cause detachment than breaks at ora.

6.Breaks with vitreous band attached to its flap are more likely to enlarge in size and cause larger detachment. Such breaks are more difficult to manage than without traction band.

7.All breaks specially holes do not require any prophylaxis. They must be observed regularly.

The common conditions that do not require prophylaxis are - Breaks surrounded by pigment all round, small holes near the ora serrata, white without pressure, retinoschisis.

Surgical treatment

Surgical treatment is the specific treatment of all rhegmatogenous retinal detachment. The outline of the principle of treatment consists of—

1.Searching and localising each and every retinal break by indirect ophthalmoscope and scleral indentation.

2.All breaks associated with detachment should be closed irrespective of their shape, size, number, by the following, either alone or in combination.

(i) Cryo coagulation, photo coagulation—Diathermy has mostly been given up in favour of the former two.

(ii) Scleral indentation either by an explant or rarely by implant. The explants are either localised plombs or large encircling bands. Sometimes local implants may be needed to be put over the large hole under the encircling band.

(iii) Drainage of sub retinal fluid is indicated in cases of longstanding retinal detachment, immobile detachment, inferior tears. In some instances a break that was not visible earlier become visible following drainage of sub retinal fluid.

(iv) Internal temponade by—Air, balanced salt solution and silicone oil.

(v) Parsplana vitrectomy—In rhegmatogenous retinal detachment, parsplana vitrectomy is required in giant tear, traction band, for gas fluid exchange.

DISEASES OF VITREOUS

Anatomy of the vitreous63,64,65

Vitreous is a semisolid transparent gel that constitutes the largest intra ocular structure. Even few decades ago it was considered to be of little significance except that it filled a large space, kept the retina in place with optical properties, and when disturbed led to unpleasant events of redness, pain, lacrimation and loss of vision. With better understanding of vitreo retinal disorders, it is clear that vitreous plays an important role in retino vitreal and retino vascular disorders.

The vitreous fills the vitreous cavity. In adults, it measures about 4 CC in volume in normal eye. It is surrounded by the posterior lens capsule, zonules, the ciliary epithelium, inter limiting membrane of the retina and the optic nerve. The main function of the vitreous is optical Its refractive index is 1.336. The other function is to stabilise the retina to which it is loosely attached without any potential space. The vitreous is attached to various intra ocular structures.

The attachments are:

1.Vitreous base—This is the strongest of all physiological attachments. The attachment of the vitreous is strongest at ora serrata. The area attached over the

ora is called vitreous base, which spans over the ora serrata about 2 mm in front and equal distance behind. The vitreous base is attached to the ciliary epithelium and blood vessels at the ora. The basal attachment lasts life long and if detached following trauma, it takes the pigment epithelium and the blood vessels alongwith. The posterior vitreous does not have firm attachment, hence is capable of detachment. Posterior vitreous detachment (PVD) is a common occurrence.

2.Round the fovea—This is a smaller, localised attachment, it is weaker than other attachments.

3.Round the optic nerve—This is fairly stronger attachment.

4.Round the retinal blood vessels—This is controversial, so are the weak attachments to the internal limiting membrane of the retina.

5.Hyaloid capsular attachment—In childhood the posterior lens capsule has a very strong attachment with the anterior vitreous membrane. The attachment is in the form of a ring to a natural depression in the anterior vitreous face. This depression is called patellar fossa or Berger’s space.

The adhesion is so strong under 25 years of age that traction on the lens fails to pull the lens out in toto, thus making intra capsular lens extraction impossible under twenty five years. The zonules, which are known as tertiary vitreous, are also strong enough to make intra capsular lens extraction impossible. The adhesion weakens with age and by sixth decade it become non existent.

In intrauterine life, the hyaloid artery traverses from the optic nerve head to the posterior part of the lens in the middle of the vitreous to form the tunica vasculosa lentis that supplies blood to the developing lens, through a space called Coloquet’s canal that disappears at birth leaving a narrow empty space which is straight at birth but becomes curved with age. It is not visible with direct ophthalmoscope. If some part of the hyaloid system has not been absorbed completely it is visible as fixed opacity in the mid vitreous without any symptoms, that may be visible as a black dot during retinoscopy.

Pathological adhesion of the vitreous

These are mostly vitreo-retinal attachment. They are found in chorio retinal scar, peripheral pigment clumps, posterior border of lattice degeneration, borders of choroidal rupture and borders of coloboma of the choroid, peripheral retinal vessels, site of retinal periphlebitis.

The shape of the vitreous body follows the shape of the globe. Its volume is less in microphthalmos. It is not capable of expanding unless something i.e. air or fluid is injected into its substance. However administration of hypertonic solutions orally or intravenous and carbonic anhydrase may shrink its volume considerably. Constant pressure on the globe forces fluid out of the vitreous and the vitreous shrinks. These two methods are employed to reduce vitreous volume during cataract surgery.

Vitreous once removed from the eye is not capable of replenishment. The space is occupied by aqueous.

The vitreous does not have a true capsule. The peripheral vitreous due to its compact collagen content is arbitrarily called cortex while the central part is called nucleus.

The vitreous is devoid of any nerve, hence it is not capable of any sensation. It has no blood supply so it is also not capable of any inflamation. However, vitreous acts as a rich medium for growth of bacteria and fungi.

The composition of vitreous

Vitreous is 98-99% water to which other solids are dissolved. The solid constituents are— Collagen, hyaluronic acid and soluble proteins. Vitreous has more ascorbic acid than in plasma. It also contains—Sodium, potassium, bicarbonates, chloride and phosphates. There are about