Ординатура / Офтальмология / Английские материалы / Pediatric Opthalmology_Mukherjee_2005

The hyperosmotic agent can either be given : (i) Orally or (ii) Intravenously. (i) The oral hyperosmotic agents commonly used are :

Gylcerol (Glycerine). This is a sweet, viscous fluid administered orally in a dosage of 1gm to 1.5 gm/kg, a single dose once or twice a day. It is generally given as 50% solution with lime or orange juice. Glycerol is distributed throughout the extra cellular body fluid. It has poor ocular penetration that helps to create a better ocular gradient to draw fluid from the eye. It is well metabolised and does not cause diuresis. Ocular hypotensive effects starts in less than half an hour, the peak is reached in one hour. The effect lasts for five to six hours. It can be administered along with CAI in reduced dose. All local antiglaucoma drugs are compatible with oral glycerine. Only side effect is nausea.

Isosorbide. This less popular oral hypotensive agent is also given as fifty percent solution that contains 1 to 1.5 gm of isosorbide per kg of body weight, about 90% of it is excreted in the urine. Peak ocular hypotensive effect is reached in one to three hours that lasts for four to six hours.

Intravenous ocular hypotensive agents :

The two drugs commercially available are : Mannitol and urea.

Out of the two, urea is no more in use due to high incidence of side effects.

Mannitol is administered as fast intravenous drip. The dose is 1 gm to 2 gm/kg or 5-10 ml/kg solution. The rate of drip should not exceed 60 drops/mt. Thus it takes about 30 minutes for 200 ml drug to be administered. It’s action starts with in few minutes, peak is reached in half and hour and effect last for six hours. It is generally given only once a day and repeated.

Surgery in childhood glaucoma :

Surgical procedures in glaucoma in general. It is difficult to classify surgical procedures in glaucoma because of diverse etiology and clinical presentation. A procedure may be suitable for congenital glaucoma i.e. goniotomy that may utterly fail in other type of childhood glaucoma. Surgery for glaucoma after ten years of age and adult glaucoma are same in principle. The procedure in childhood requires adequate modification.

The aim of surgery. The aim of surgery is to give stable, near normal intraocular pressure that prevents further field loss and changes in optic nerve head. A well executed surgery generally meets with above criteria but many a times a particular surgery may fail altogether and require either re-operation or addition of medical treatment. Even when a surgical procedure does not fail it may just be a partial success needing other modes of lowering IOP.

Surgery may be

1.A primary procedure.

2.May follow when medical methods have failed.

3.May be repeat procedure.

Following is an outline of various types of glaucoma that requires different procedures :

1.Glaucoma in childhood :

(a) Congenital primary glaucoma

(b) Congenital glaucoma associated with anomalies of anterior chamber and angle. (c) Glaucoma in older children.

(d) Secondary glaucomas.

2.Glaucoma in adults :

(a) Wide angle glaucoma (b) Narrow angle glaucoma

(i) With pupillary block (ii) Without pupillary block.

3.Absolute glaucoma :

The other possible classification is according to anatomical location of the surgery.

1.Surgery on the iris

2.Surgery on the angle of AC.

3.Filtering surgery.

4.Drainage device

5.Cyclodestructive procedures.

1.Surgery on the iris :

(a) Surgical procedures consist of : (i) Peripheral basal iridectomy

(ii) Sector or broad based iridectomy (iii) Button hole iridectomy

(iv) Sphincterotomy (v) Four dot iridotomy

(b) Laser procedures on iris—Laser iridotomy—Argon, NdYAG

2.Surgery on anterior chamber angle :

(i) Primary where the surgical procedure involves the trabecular meshwork only : (a) Goniotomy

(b) Trabeculotomy

(ii) As part of filtering surgery.

Thermal sclerotomy, corneoscleral trephine, iridencleisis, cyclodialysis

3.Glaucoma surgeries can either be a non filtering or a filtering procedures. In the latter the aqueous drains either outside the eye in subconjunctival space as in trabeculotomy or may drain in suprachoroidal space as in cyclodialysis. In trabeculactomy a part of trabecular meshwork is removed. In other procedures the aim is not to disturb the trabecular meshwork.

4.Aqueous drainage devices (See page 350.)

The non filtering surgeries are :

1.Paracentesis. This gives a short term lowering of IOP which returns to previous level in few hours to few days generally used in secondary glaucoma.

2.Goniotomy and trabeculotomy. They are meant to give sustained lowered IOP.

Various methods employed to lower sudden rise of intraocular pressure :

Acute rise of intraocular pressure may occur—as part of ocular disease i.e. primary or secondary acute glaucoma that may be iatrogenic as is common in various retinal surgeries. A growth may press the globe from outside. The procedures to reduced acute rise of IOP are :

1.Paracentesis—This is indicated in acute secondary rise of tension.

2.Retrobulbar of anaesthesia

3.Removal of external implants in retinal surgery.

4.Bollus IV mannitol.

5.Massage of

1.Globe

2.Cornea

3.Orbital contents.

Massage of globe and cornea force the aqueous out of the anterior chamber either with normal or wide angle. This method is used prior to lens extraction. The closed angle may open up in acute narrow angle glaucoma for a short time following massage of the globe.

The mode of action of orbital massage is not well understood. It has effect of bulbar massage as far as intraocular tension is concerned. Otherwise it expels fluid from retrobulbar structures and muscles. This method is more effective following retrobulbar and peribulbar anaesthesia. Relaxation of extraocular muscles, reduce tension over the sclera. This method is also used in cataract surgery, has no role in glaucoma. However gentle massage of the globe through the lid may be used in failed surgery to re-establish the fistula.

Non filtering surgery with permanent lowering of IOP :

1.Surgery to relieve pupillary block.

2.Cyclodestructive procedures.

1.Surgery to relieve pupillary block :

(a) (i) Peripheral button hole iridectomy. (ii) Peripheral basal iridectomy

(iii) Sector iridectomy (b) Iridotomy

(i) Laser iridotomy (ii) Four dot iridotomy

(c) Sphincterotomy and iridoplasty

2.Cyclodestructive procedures :

(a) Cyclo cryo

(b) Laser cyclo ablation

(c) Ultrasonic cycloablation (d) Cyclodiathermy

Filtering surgeries

1.External filtration procedures

2.Internal filtration procedures

1.External filtration surgeries are :

A.Trabeculectomy

B.Sclerotomy

C.Sclerectomy

D.Iridencleisis

E.Corneo scleral trephine

F.Cyclodialysis

G.Glaucoma valves

2.Internal filtering surgeries are :

(a) Goniotomy

(b) Goniopuncture

(c) Trabeculostomy

Surgical procedures for glaucoma in children :

1.Goniotomy

2.Goniopuncture

3.Trabeculotomy

4.Combined trabeculotomy and trabeculostomy

5.Thermal sclerotomy

6.Shunt operations

7.Cyclodestructive surgeries

8.Iridotomy

Laser in glaucoma

1.General information about ophthalmic laser.

2.Various uses of laser in glaucoma.

General information about ophthalmic laser. Laser is an acronym of light amplification by stimulated emission of radiation115, 116. Laser is artificially created bright light with high source of energy that is formed when electric charge is passed through a medium. The medium can be gas, liquid or solid. The media generate photons to emit light energy.110

The light produced by laser is of uniform in frequency and direction.111

(a) Usual laser consist of—112, 120

(i) Source of energy. Energy used is generally electric discharge or burst of white light.

(ii) The medium that generates light energy by emitting photons.

(iii) A chamber (lasing cavity) to reflect energy back and forth by mirrors, one at each end of the chamber. One transparent, only to emit laser and other totally reflecting mirror. It also houses the medium.

(iv) Aperture to control laser output.

(v) Delivery system. The delivery system can be a slit lamp, an ophthalmoscope, an endoscope, an operating microscope or a surface probe.

(b) Properties of laser. The laser is near parallel, coherent, monochromatic linear, unidirectional, light that can be converted into heat when absorbed by tissue.

The laser can be delivered either as continuous wave or in pulse.113 Property, colour and mode of action of laser depends upon wave length and pulse duration. Wave length of laser used in ophthalmology vary between 193 nm (Excimer) which is nearer to ultraviolet and 1060 nm (carbon dioxide) which is nearer to infra-red.

Ophthalmic laser passes through clear ocular media without being absorbed except excimer. Laser can get absorbed in hazy media i.e. senile sclerosis of lens. Damage to cornea and lens is more with long wave laser like neodymium (1016 nm) and CO2 (1060 nm). Darker tissues absorbs laser better than lighter tissue. Laser is absorbed by melanin in uvea, RPE, xanthophyll of macula and haemoglobin.

The density of photons depend upon spot size of laser and power used. Density of photons increases as spot size is reduced. Energy used in laser is expressed in Joules (MJ) or Watts (Mw) depending upon the mode of transmission. A continuous wave laser like argon is expressed in watts while NDYAG which is pulsed laser is expressed in Joules.

C.Various types of accessories used with ophthalmic laser are cooling system and various types of condensing lenses that concentrate the laser beam at desired spot i.e. Abraham’s lens or a gonioscope to direct beam on the trabecular meshwork.

D.Lasers have various modes of applications in ophthalmology. All of them are not used in glaucoma. The common uses of laser are :

(i) Photodisruption to do capsulotomy, iridotomy and rupture the vitreous face.

(ii) Photocoagulation of vessels and to create a chorioretinal scar in disorders of choroids, retina and vitreous.

(iii) Photo vaporising is utilised in vitreoretinal vascular disorders and to seal fibrovascular fronds at the time of vitrectomy in association with photo coagulation.

(iv) Photo radiation is used in malignant melanoma of choroids and A.M.R.D.

(v) Photo sublimation is used in excimer laser, which acts without heating or coagulation.

E.Laser is delivered to cornea, iris and after cataract by directly focusing the target issue. Intraocular delivery is achieved either by transpupillary or transscleral route.

Transscleral route is used in diode laser, which is absorbed minimally by the sclera.

F.Types of lasers used in ophthalmology can be solid state or gas lasers. The former consist of Ruby and Nd-YAG while latter laser consists of argon, carbon dioxide, krypton, helium, neon, excimer etc.

(i) Argon Laser. Argon Laser is one of the most commonly used lasers in ophthalmic disorders. It is used to treat disorders of both anterior segment as well as posterior segment. It has no use in corneal diseases. The medium is argon gas that works on an electric discharge. Wave length for blue argon is 488 nm, green argon has wave length of 514 nm. It is a continuous wave laser. The energy is in watts. It is least absorbed by ocular media but well absorbed by melanin, retinal pigment epithelium, haemoglobin and xanthophyll making it very useful for treatment of glaucoma and vascular retinopathy, as it is absorbed by xanthophyll, it should not be used too close to the fovea.

In glaucoma it is used to perform argon laser trabeculoplasty in open angle glaucoma and laser iridotomy in angle closure glaucoma. It has no use in congenital glaucoma and most of the childhood glaucoma except to establish a passage between AC and PC in limited cases. It is delivered either by slit lamp or by fibre optics endoscope for intraocular lesions. To be effective in ALT, a suitable gonio lens and for iridotomy an Abraham’s lens is used.

The Abraham’s lens114 consists of a contact lens which looks similar to Goldmann three mirror gonioscope. On the anterior surface, a plano convex lens of +66D is glued. The plus lens is decentred to focus the laser beam on the iris. The function of the lens is to double the diameter of the beam on the cornea and reduces the beam diameter to half on iris. The advantage of this is that it reduces power density at the cornea to one fourth and increases it by a factor four on the iris. The Wise lens has a button of +113D.115 This is not used very widely. The Abraham lens can be used both for argon and NdYAG laser while using argon laser the magnification in the slit lamp should be x40.114 Optics of eye under treatment does not take any part during argon laser treatment.

II. NdYAG Laser (Neodymium Yuttrium Aluminium Garnet). It is commonly used laser for capsulotomy in aphakia and pseudophakia. It can also be used on iris. In this the neodymium atoms are embedded in crystal of yuttrium, aluminium, garnet and energised by xenon flash light.112

It works by photodisruption of tissue. Its function is independent of pigment absorption. It works on relatively transparent media like posterior capsular opacification, after cataract and anterior vitreous band. It has a short pulse but a long wave length of 1064 nm. Its power is set in Joules.

When a tissue is exposed to NdYAG, the tissue is ionised and plasma is produced. The plasma has mechanical properties of gas and electric properties of metal. Expansion of plasma sends waves inside the eye. Shock produced by these waves mechanically disrupts the tissue. The shock waves can be transmitted to the retina causing retinal detachment. NdYAG laser can be used to do iridotomy, iridoplasty and cyclo-ablation.

Advantages of NdYAG. When compared to argon laser, the NdYAG laser has following advantages :

—Action of NdYAG is independent of absorption by pigment hence it is most widely used laser for capsulotomy.

—Its action on light coloured iris is as good as dark coloured iris. Latter requires more energy than former.

—Number of burst in NdYAG is almost one tenth of that required for argon laser.

—Argon laser produces more tissue edema than NdYAG.

—Iridotomies done by NdYAG are well circumscribed and have less chances of closure. Pupillary distortion is less in NdYAG.

The disadvantages of NdYAG are :

—Hyphaem : is short lived and stops by pressure bandage. The other disadvantage is retinal detachment in predisposed eye.

(iii) Diode Laser. This is a semiconductor solid state laser where two light emitting diodes are used to produce wave length between argon and NdYAG (800-820 nm). Its absorption by melanin is better than that by NdYAG. It has better scleral penetration than argon. It does not require separate cooling system. Its small portable size, durability and low cost of maintenance makes it very popular ophthalmic laser. It is used in treatment of choroidal neovascular membrane without damaging nerve fibre layer above it and for cycloablation. It can be used either through the pupil or over the sclera.

(iv) Krypton Laser. There are two types of krypton lasers i.e. yellow and red. Krypton laser is poorly absorbed by haemoglobin and xanthophyll. This makes it useful in treatment of lesions near the macula. Good chorioretinal sear makes it useful in treatment of retinopathies associated with haemorrhage. Presence of blood in vitreous and moderate opacities do not hamper its use.

(v) Carbon dioxide laser. It has longest wave length among all ophthalmic lasers i.e. 10,600 nm, which is nearer to infra-red and invisible. It is mostly used in occuloplastic surgeries. Its photo evaporation property is used for treatment of cutaneous nevus.

(vi) Ruby Laser. This was the first laser used in ophthalmology. Now this is no more used as better lasers are available.

(vii) Excimer laser. The word excimer is contraction of two words i.e. excited and dimer (excited dimer). Dimer is a molecule created by the mixture of gas halogen. When these dimers are subjected to electric field, they are transformed to higher discharge. The excimer has shortest wave length among all ophthalmic lasers. Its wave length varies between 193 nm when argon fluoride is used, to 351 nm when krypton fluoride is used.

Excimer laser is absorbed by all layers of the eye specially cornea. This property has been utilised to reshape cornea in treatment of refractive errors i.e. P.R.K., laser in situ keratomileusis (lasik) photo therapeutic keratectomy, removal of superficial corneal opacities 116 and lasek (laser sub-epithelial keratomileusis).

The most commonly used wave length is 193 nm because it is just sufficient to break up interatomic links without effecting adjacent tissue. Thermal effect is minimal. Excimer has no use in any type of glaucoma.

2. Various uses of laser in glaucoma122, 123, 124. From the previous paragraphs, it is clear that all glaucomas are not suitable for treatment by all laser procedures. There are specific procedures for specific groups of glaucoma. Laser is not a suitable mode of management

of glaucoma in children in general and congenital primary glaucoma in particular.

Overall result of laser treatment for glaucoma under thirty years of age and secondary glaucomas is unsatifactory. However laser iridotomy has definite places in pupillary block glaucoma. Argon, NdYAG and diode lasers are the commonly used lasers for glaucoma.

Commonly used laser procedures in glaucoma are122, 123, 124

(a) Iridotomy

(b) Trabeculoplasty (c) Gonioplasty

(d) Cyclophoto coagulation

(e) Panretinal photo coagulation (f ) Suturelysis

(g) Bleb failure.

(h) Laser scarring to reduce over filtering bleb also. (i) Gonio photo coagulation

(j) Goniopuncture

(k) Opening failed sclerotomy (l) Cycloablation

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