Ординатура / Офтальмология / Английские материалы / Pediatric Opthalmology_Mukherjee_2005

Similarly a person who has been in dark for some time, when he goes out in bright light takes few seconds to get adapted to the bright light.

The instrument is called dark adaptometer that is used in cases of defective night vision due to diseases of retina and choroid. It is used mostly in rod disorders and has less utility in cone disorders.

Light sensitivity of the eye has three grades:

1.Photopic — Bright light, normal room light or outdoor, this is cone function.

2.Mesopic — Dim room light or twilight, this is partly rod and partly cone function.

3.Scotopic — This is in a room without light or dark night outside, this is rod function.

Commonly used dark adaptometer is Goldmann Weeker’s adaptometer. Besides this there are other adaptometers like—Feldman adaptometer, Henkind and Seigel scotometer, Comberg’s nyctometer.

To perform the test both the pupil are fully dilated. The patient is made to sit in a semidark room to get dark-adapted for few minutes. Then the eyes are exposed to bright light similar to pre-adaptation light for six to eight minutes. Dark adaptation is started. Retinal sensitivity is tested for first ten minutes at an interval of ten seconds then every one minute, first in ascending order i.e. the light sensitivity is gradually increased until the patient becomes aware of it, then the illumination is gradually reduced until the patient can not see the light. The average of the two is plotted against time. Illumination is plotted vertically and time horizontally. The normal dark adaptation graph is biphasic. It comprises of two concave curves joined to each other. The first part is short and steep, lasts for initial ten minutes and denotes cone threshold while the remaining a longer and shallower curve denotes rod threshold and lasts for about 30 minutes. The junction of the two is calledrod-cone-break.38 The rod threshold is prolonged in retinitis pigmentosa, vitamin A deficiency, retinitis albi punctatus.39

Electro retinography38,40

This is an objective method to measure retinal function. It is used to detect function of both rods and cones, was mostly used for peripheral retinal disorders. With development of better computerised methods it is now being used more frequently to assess macular function as well especially in colour vision defects41 It is relatively crude method where all the layers of the retina participate. However involvement of rods, cones, bipolar cells and Muller’s cell are reflected better than remaining layers. This is brought about due to transmission of ions across the retina.

The test is done by a computerised oscilloscope that gives a visual picture on a screen which may be obtained as print out (electro retinogram) for permanent record. The instrument has two electrodes, one is a modified contact lens that is applied to cornea and the other electrode is applied on the forehead.

ERG can be photopic for cones, scotopic for rods. It can be for colour. Mostly used colours are red (long wave) or blue (short wave). A mesopic response can be seen on the ascending arm of the b wave.

The electro retinogram is a continuous tracing along a straight line. The spike below the base line is called negative while those above are known as positive waves.

The various components of ERG are:

1.Early receptor potential (ERP)

2.a wave

3.b wave

3.c wave

4.d wave

Out of these only a and b waves have clinical significance.

The a wave is a small negative wave, due to hyper polarisation of rods and cones.

The b wave is the largest wave both in amplitude and duration. It is a positive wave, it is due to elevation of extra cellular potassium.42

The waves are measured in amplitude and time. The amplitude is measured in microvolts and time is measured in milliseconds.

Method

The pupil is fully dilated. The eye is adapted, then flash stimulus are given and the electro retinogram is obtained.

Uses of ERG are many. They are all diagnostic and have some prognostic value.

1.Diagnose retinal degeneration and dystrophies.

2.They are utilised to differentiate between disorders of rods from cones.

3.They are used to detect possibility of presence of retinal degeneration in the asymptomatic members of the family.

4.They can be used to detect malingers.

5.They may be used to assess retinal function in presence of opaque media.

The common conditions where ERG is useful in conforming the diagnosis are:

•Retinitis pigmentosa and allied retinal degeneration

•Lebers congenital amaurosis

•Achromatopsia

•Congenital stationary night blindness

•Oguchis disease

•Choroideremia

•Gyrate atrophy of choroid

•Quinine amblyopia.

It has no role in ganglion cell disorder, hence it is not used in glaucoma and diseases of optic nerve.

Rubella retinitis gives fundus picture similar to retinitis pigmentosa but have normal

ERG.

The female carriers in X linked retinitis pigmentosa may show abnormal b wave in absence of night blindness.

The ERG may be extinguished in advanced retinitis pigmentosa and allied conditions, total retinal detachment, diffuse unilateral sub acute neuro retinitis, ophthalmic artery occlusion.

Electro oculograph42

Electro oculograph has relatively less use than ERG in evaluating the retinal functions because in most of the cases that have, either absent or grossly subnormal ERG, also have subnormal EOG except in few cases i.e. stationary night blindness, X linked retino chisis, dominantly inherited Best’s vitelli form, macular dystrophy.38

Electro oculography like ERG is an objective method to measure the retinal function like ERG. It also measures mass response of retina. It basically measures difference in cornea and retinal potential on horizontal movement of the eye. The corneal potential is positive while the retinal (back of the eye) is negative. The difference between the two is 6 mv. The difference depends upon excursion of the eye, level of illumination and adaptation.

It is also useful in some conditions of subtle extra ocular muscle palsy with modification. It can also be used to record nystagmus, where the instrument is called electro nystagmograph.

The instrument is an oscilloscope. It has two electrodes, one is attached near the medial canthus and the other near the lateral canthus. The former is corneal electrode and is positive while the latter is retinal electrode and is negative.

For retinal function test, it indirectly records the standing potential of the eye, which is caused due to voltage difference between inner and outer retina. It evaluates retinal pigment epithelium mostly.

To get the reading the pupil is dilated. First, the patient is dark adapted. The electrodes are placed one on the medial canthus and the other on the lateral canthus. The patient is asked to move the eye alternately, medially and laterally with approximate 60° excursion between the two. The oscilloscope is activated and the spikes noted. After dark adaptation the response progressively decreases reaching the trough in 8-12 minutes, which is lower than the base line. The light adapted trough is well above the base line and is reached in 6-9 minutes. The whole process requires about 20 minutes for each eye. To obtain the graph, the amplitude in microvolts is plotted against time. The final reading is a ratio between the light peak and dark trough called Arden ratio i.e. Maximum height of light/depth of the dark trough. The normal is 185 or more. Reading between 125 and 150 is subnormal and less than 125 are flat. The response is independent of opacity in media. Myopia, trauma and ocular surgery give low response.

Visual evoked response (VER)

This is an objective test to assess function of visual path beyond the retinal ganglion cells. It is commonly used to access macular as well as optic nerve function in pre geniculate path. It has some use in amblyopia and colour blindness. It is basically modified form of electroencephalogram. It records electric activity of the visual cortex area 17,18 to light stimulus. The VER records primarily the central visual function43. Opacities in the media do not influence the response.

The VER is of two types:

1.Flash VER

2.Pattern reversal VER

A typical pattern consists of a latency of 75-80 ms and a positive wave of 110 ms. The positive wave has a peak of 9 ms.

Method of recording

The patient sits in a quiet dark room for sometime in front of a screen at a distance of 1.5 metres. One eye is tested at a time. The potential is recorded by an electrode placed over the occiput. The other electrode is put on the vortex. Hundreds of responses are summated and averaged by a specially programmed computer.

In case of flash VER, a flash of light is used to start the response. In case of pattern reversal VER, a chequer board with alternate black and white squares of equal size and intensity are displayed on the screen. The colour of the squares can be reversed i.e. the black becomes white and white becomes black. The flash VER is used to test the function of the macula and visual pathway in non verbal children, mentally retarded children and aphasic children.44 It can detect malinger and visual potential in opaque media especially in large corneal opacity where the pupillary reaction can not be elicited.

The form reversal VER uses form sensation hence this gives a rough idea of visual acuity. VER is useful in optic neuritis due to demyelinating disease where VER may be absent in acute stages. VER is abnormal in multiple sclerosis even before diminished vision sets in. It is useful in compression lesions of optic nerve. In cortical blindness the response is absent.45,46

Photo stress test

This is a crude form of dark adaptation test. The visual pigments are rendered insensitive to ordinary light causing a temporary relative scotoma which passes in some time with fading of scotoma. The recovery time depends upon ability of the photo receptors to re-synthesise visual pigment. This is used for macular lesion and has hardly any use in peripheral disorders. This differentiates macular cause of loss of vision from optic nerve cause.

To perform the test, the distant vision is recorded with best correction. Then the eye is dazzled by the light of indirect ophthalmoscope kept at about 3 cm from the eye and the patient is asked to read the best corrected line. Normally it takes about 30 seconds to recover. In a case of macular disease, this is prolonged over 1 minute. Visual loss due to optic nerve lesion is not effected by photo stress.

Interpretation of physical examination of retina (Signs of retinal disorders)

The signs of retinal disorders are many and varied. They depend on part of the retina involved and associated involvement of vitreous, choroid and optic nerve.

The signs may be limited to retina only where it can be central (macular), peripheral or combined. The signs can be secondary to choroid as chorio retinitis. This is more common than reverse i.e. retino choroiditis that is pathology spreading from retina to choroid. However neuro retinitis is as common as inflammation spreading from retina to optic nerve. Tumours of optic nerve do not metastasise in retina. But spread of retinoblastoma through optic nerve is common.

Duration of the disease too plays an important role in appearance of the signs.

The common signs are:

Signs of retinal disorders are essentially situated on the fundus which is visible either by ophthalmoscope or by slit lamp.

They are changes in the blood vessels, they include—1. Attenuation, 2. Dilatation, 3. Tortuasity, 4. Anastomosis.

Attenuation. Normal arteries are thinner than veins but in some pathological cases the arteries become thinner than normal or may look to be so if the veins are dilated. The thinning can be generalised or localised. Generalised thinning is more common than segmented attenuation. The most common causes of generalised thinning of the arteries is retinitis pigmentosa and allied conditions. Other causes of attenuation like arterio sclerosis and hypertension is not seen in children. However retinal artery occlusion may occasionally seen in children. Commonest cause being embolism from the cardiac valves in sub acute bacterial endocarditis. In post papilledematous and consecutive optic atrophy, there is thinning of the arteries.

Dilatation of arteries is far less common, it is seen in leukaemia and in angiomatosis retinae or cirsoid aneurysm of the retina. Dilatation of the veins is more common. It is seen in cases of papilledema and venous obstruction. In angiomatosis retinae the vein may be greatly dilated.

Tortuosities of both arteries are uncommon in children. They are mostly seen as congenital anomalies like angiomatosis, Coat’s disease, telangiectasis.

Anastomosis. Anastomosis between two systems of circulation i.e. retinal and ciliary and between artery and veins are always pathological.

The effect of abnormal vascularity leads to:

1.Hyperemia of the retina

2.Anaemia of the retina

3.Edema of the retina

4.Exudates on the retina

5.Haemorrhages on the retina

6.Neovascularisation.

Hyperaemia of the retina may be arterial or venous. Arterial or active hyperaemia is seen in dilatation of the arteries and increased tortuosity of the retina. It can be generalised or localised. Common causes are retinitis and uveitis.

Venous or passive congestion is caused due to impeded venous outflow. Common causes being papilledema and papillitis. Other causes are systemic condition like leukaemia, polycythemia and chronic heart failure. Children in teens may have periphlebitis. Other causes are sickle cell retinopathy and cavernous sinus thrombosis. Diabetes and hypertensive retinopathy rarely cause hyperaemia in children.

Anemia

Commonest cause of pallor of retina is systemic anemia. Not only the general appearance of the retina is pale but the optic nerve also looks pale. Anemic fundus is common in leukemia

and lipidosis also. Pallor can be true pallor due to diminished blood supply or may look pale with normal blood supply Arterial obstruction is the commonest cause of pallor. It may be generalised when the main trunk of the central retinal artery had been obstructed or segmental when one of the branches has been obstructed. Other causes of generalised pallor of retina with normal blood supply and normal haemoglobin are albinism, myopia, Waardenburgs syndrome, choroideremia.

Causes of localised pallor are- Retinal edema, coloboma of retina, retino schisis, flat retinoblastoma, atrophic areas.

Retinal edema

The main pathology in retinal edema is break down of blood retinal barrier, either the inner barrier or outer barrier. This is brought about by any of the following two or combination of the two—1. Excessive leak of fluid from capillaries due to increased permeability as is seen in inflamation or vascular retinopathy. 2 Break down of larger protein molecules.

Break down of the inner blood retinal barrier leads to localised edema as cystoid macular edema or post traumatic edema. Diffuse retinal edema is seen in vascular retinopathies. Break down of outer blood retinal barriers lead to central serous retinopathy and wet type of age related macular degeneration. Retinal edema has greater predilection for posterior pole mostly macula.

The common causes of retinal edema in children are—blunt injury, optic neuritis, papilledema, neuro retinitis, retinitis, chorio retinitis, retinopathies, cystoid macular edema.

Edema of the macula is associated with diminished central vision, there may be acquired hypermetropia, central scotoma, metamorphopsia. Peripheral retinal edema may be symptomless or may be associated with localised scotoma.

It is difficult to detect mild retinal edema with ophthalmoscope. In moderate edema the retinal surface has an albuminous appearance, the retina looks thickened and has granular appearance. Macular edema generally presents with a circular raised area. A macular edema is said to be clinically significant macular edema if it has following features-

1.Retinal edema is within 0.5 mm of fovea centralis

2.Retinal edema is larger than 1 disc diameter within one disc diameter of fovea.

3.Hard exudates within 0.5 mm of fovea associated edema of the retina near by.

Presence of any one of the above is diagnostic47

Clinically significant macular edema is best elicited by + 90 D on slit lamp biomicroscopy. Separation of nerve fibres due to accumulation of fluid near the disc is visible with red free light of ophthalmoscope.

Exudates on the retina

Presence of retinal exudate is always pathological. There are conditions that look like exudates but are not exactly exudates. Common among them are- Small opaque nerve fibres and drusen of the retina.

Clinically exudates have been classified into two types on the basis of their ophthalmoscopic appearance. They are:

1.Soft exudates

2.Hard exudates

Soft exudates. They are due to disturbance of axoplasmic flow that result in accumulation of axoplasmic waste product in the nerve fiber layer, hence they are called superficial exudates. Their cotton wool appearance imparts the term soft exudate to them. They are basically vascular in nature. There is sudden focal obliteration of capillaries in small areas resulting in ischemia followed by anoxia. The infracted area leads to proliferation of neural element in the retina. The soft exudates are white in colour, their edges are irregular or feathery, they are scattered, do not coalesce to form specific pattern, are acute in onset, disappear in two to three month. On fluorescein angiography, they are non fluorescent, surrounded by area of dilated capillaries. Common causes are retinitis, hypertensive retinopathy, severe anemia, dysproteinemia, collagen diseases, angiomatosis, telangiectasis. leukaemia, trauma, papillitis, papilledema, septicimia, rheumatic heart disease, sub acute bacterial endocarditis.

Hard exudates. Though they are seen more commonly in vascular retinopathy, there are more of exudative nature than vascular. To begin with there is neural degeneration due to defective oxidative process. The products of degeneration are generally lipid in nature, may be associated albumin, cholesterol, hyaline material or even calcium. They are situated in deeper layer of the retina hence are known as deep exudate. They are round in shape with clear-cut edges, size may vary from pin head to as large as disc, generally seen in posterior pole and are always underneath the blood vessels. Lipid content is most probably the causes of their yellowish grey colour. They are responsible for formation of macular star and arranged in a wreath like pattern in non specific circinate retinopathy. They develop over months and take months to disappear.

Common causes of hard exudate are—Diabetic retinopathy, late stages of hypertensive retinopathy, Doyne’s choroiditis, disciform degeneration of macula, Coats disease.

Both the types of exudates may exist in the same eye at the same time and one may be superimposed on the other. Both the types are non-specific, may be present without haemorrhages. However presence of haemorrhage along with exudate is very common.

Retinal haemorrhage

Retina is supplied by an elaborate network of blood vessels with large capillary bed. Hence bleeding from them is very common.

The causes of retinal haemorrhages are many. Sometimes more than one causative factor may be responsible.

Causes of retinal hemorrhages can be broadly divided into:

1.Traumatic. Closed globe and open globe.

It is common for retinal vessels to be torn in traction retinal detachment, however there may be tear in the blood vessels in rhegmatogenous retinal detachment as well.

2.Inflammation. More common cause is periphlebitis, less common is periarteritis.

3.Retinopathy. Perhaps largest numbers of retinal haemorrhages are seen in various types of retinopathies, fortunately many of them are not seen in children. Common

retinopathies are—Sickle cell retinopathy, malignant hypertension and nephritis.

4.Blood disorders. Anaemia, leukemia, purpura, haemophilia, sickle cell anaemia are common in children.

5.Miscellaneous. Papilledema, papillitis, telangiectasis, hamartomas, Coats disease, retinoblastoma

6.There are two conditions that are not true hemorrhages but look like hemorrhage:

(a) Cherry red spot (b) Macular hole

Causes of cherry red spot are:

1.Various errors of metabolism and storage diseases - Tay Sach’s disease, Niemannpick disease, Farber’s disease, Sandhoft’s disease, Hurler’s disease, mucopolysaccharidosis.

2.Central retinal artery occlusion (rare in children).

Types of retinal haemorrhages

Depending up on anatomical location of the hemorrhage in relation to the retina they have been divided into following groups:

Inter retinal haemorrhages

There are mostly capillary in nature but occasionally can be arterial or venous. They are called superficial when they are in the nerve fiber layer. Superficial haemorrhages are bright red in colour, are typically flame shaped or leaf shaped with irregular border. They are deeper to the retinal vessels and are known to fade over weeks to months without treatment. Their number and size may vary from single to multiple, from small spots hardly visible to larger than manydisc diameter. They may be localised or scattered. Peripheral hemorrhages do not cause visual disturbance but a small hemorrhage on the fovea causes extensive visual loss. The hemorrhage themselves are non fluorescent and block fluorescein. Common causes are hypertension, papillitis, papilledema, retinitis and trauma.

Roth’s spots are peculiar superficial haemorrhages, which are flame shaped haemorrhages with central white area commonly seen in sub acute, bacterial endocarditis, anaemia and purpura.

Deep haemorrhages

Haemorrhages in deeper layer are small, circular. Their colour is less brighter than superficial haemorrhages. Compactness of the deeper layers of the retina prevent them to spread, hence

they are localised and small dot shaped. The retinal vessels pass over them, commonly found in the posterior pole, may be scattered or may be in bunches mimicking retinal micro aneurysm from which they are differentiated by fluorescein angiography. The deep haemorrhages are not fluorescent and block the fluorescein. The micro aneurysms are fluorescent. Commonest cause of deep haemorrhages is diabetic retinopathy. It is not uncommon to see mixture of both superficial and deep haemorrhages in the same eye in case of diabetic retinopathy.

Sub hyaloid haemorrhage

These are also known as pre retinal haemorrhages. They occur between the internal limiting membrane of the retina and vitreous without invading into the substance of the vitreous. The source of the bleeding is retinal vasculature. They are relatively rare but not altogether absent in children. They may be seen even in new born.

The common causes in children are—Blunt trauma, retinal tear with or without detachment, Purtscher’s retinopathy, penetrating injury, accidental perforation of the globe during squint surgery.

Children in second decade may develop pre retinal haemorrhage in retro lental fibroplasia, persistent hyaloid artery, Coat’s disease, angiomatosisretinae, juvenile retino schisis, and drusen of optic nerve.

Periphlebitis retinae (Eale’s disease) is commonest cause of pre retinal and vitreous haemorrhage in young male adults. Commonly seen in third and fourth decade. Eale’s disease may have an early onset, may be seen as early as fifteen to sixteen years. Similarly diabetic retinopathy is commonest cause of pre retinal and vitreous haemorrhage after fourth decade. In rare instances untreated juvenile diabetes may present as retinal or pre-retinal haemorrhage.

Characteristics of pre-retinal (sub hyaloid) haemorrhages

Symptoms and signs depend upon position of the haemorrhage, size of the haemorrhage and associated lesions.

Symptoms

It may be symptomless if the haemorrhage is in the lower part of the retina, away from the macula. Peripheral haemorrhage may go unnoticed.

A lesion in front of the macula is cause of sudden painless loss of vision. In very large haemorrhages vision may be reduced to hand movement with good projection. A patient with fresh haemorrhage may complain of red vision (erythropsia) which passes off in few days. Generally vision improves with passage of time and may return to normal as blood absorbs. The patient may complain of black spots, after the vision has come to normal.

A typical sub hyaloid haemorrhage if seen within few hours of onset, starts as a circular patch of bright red spot generally in the posterior pole. Gradually the heavy particles of blood settle down at the bottom of the original oval patch. The upper border becomes straight and parallel to the ground and retains its bright red colour. The upper part contains serum hence is either clear or yellowish in colour. The sub hyaloid haemorrhage has no tendency to clot. In case of Terson’s syndrome, a sub-arachnoid haemorrhage may find its way on the retina along the optic nerve and may look flame shaped and rarely keel shaped which is a common appearance of pre macular haemorrhage.

All the cases with sub hyaloid haemorrhage should routinely be examined under mydriasis with indirect ophthalmoscope. The advantages of examination by indirect ophthalmoscope are that it can circumviate a large haemorrhage, and makes examination of the retina possible inspite of its presence. It gives excellent information for peripheral-lesions especially in periphlebitis. It also gives information about the haemorrhage in three dimension.

Vitreous haemorrhage

So long the outer membrane of the vitreous is intact, it is not affected by haemorrhage. Only when new blood vessels grow in the vitreous, a haemorrhage develops. A small haemorrhage initially behaves like a pre retinal haemorrhage. The causes of vitreous haemorrhages are the same as pre retinal haemorrhage. Generally the haemorrhages absorb without any treatment within days to weeks. However if bleeding occurs frequently, the clearance time is proportionally prolonged and a stage may come when the haemorrhage does not clear and a stage of hemophthalmos develops, which may require vitrectomy followed by endo laser photo coagulation.

Fate of retinal haemorrhages

Most of the fresh and small haemorrhages absorb without leaving any trace. This happens following hemolysis of RBC when there is no repeat bleeding and the haemorrhage is small. In case of multiple haemorrhages, larger the size, longer is the time taken for absorption. This is generally followed by proliferation of glial tissue called retinitis proliferance, which are vaso proliferative in nature. The proliferation can be from the superficial layer of the retina or the retinal blood vessel. The bands develop more commonly near the disc and extend into the vitreous body. They may be only a few or very extensive. Fine capillaries develop along or on the proliferative bands. As these vessels are unsupported, they bleed more commonly than other retinal blood vessels. The conditions that cause retinitis proliference are—Trauma mostly penetrating, retained intra ocular foreign bodies, retro lental fibroplasia, angiomatosis retinae, Coat’s disease, sickle cell retinopathy, Eales disease. In contrast to this common causes in adults are—Eale’s disease, proliferative diabetic retinopathy and venous occlusion.

Sub retinal haemorrhage

They are not true retinal haemorrhages, they are in fact choroidal in nature. The bleeding occurs between the pigment epithelium of the retina and the choroid. They are less frequent in children than in adults.

Frequent causes of sub retinal haemorrhage are - Blunt trauma, choroidal rupture, myopia, drusen of optic nerve head, chorio retinitis and rubella retinopathy.

The sub retinal haemorrhage looks like blackish oval raised area over which retinal vessels pass. The lesion is better visualised by indirect ophthalmoscope and biomicroscope, confirmed by fluorescein angiography and ultrasonography. The basic pathology is formation of new vessels under the retina.

Retinal aneurysm

They are very common in adult diabetics, occasionally can be seen in juvenile diabetic. In adults, they are small hence are called micro aneurysms. In children they are relatively larger. On fundus examination they look similar to bunch of deep haemorrhages. They are best