018 112 Laser in Ophthamology.cdr by wanghonghx


									 Muhammad Faheem
 Faisalabad, Pakistan                                                                           IR-112

                                          LASER IN OPHTHAMOLOGY
                        Introduction                            The intense light from the sun has
                        Laser meaning “Light amplification      been known for centuries to cause
                        by stimulated emission of radiation”    ocular damage. The Roman fleet is
                        A laser beam is a single wavelength,    stated as having had solar power
                        monochromatic, coherent parallel        directed at them at the Battle of
                        light beam usually of high energy.      Syracuse by Archimedes in 212BC.
                        Wavelengths are measured in             From the beginning of this century it
                        nanometers (nm).1nm = one               was realized that eclipse blindness
                        thousand millionth of a meter. Laser    was caused largely from the thermal
                        beams are produced by the               component in sunlight rather than
                        excitation of atoms to a higher than    the visible radiation. In addition
                        usual energy state. Coherent            infrared radiation induces thermal
                        radiation is given out (emitted) as     damage when viewing through any
                        the atoms return to their original      optical device. American work in
                        energy levels.                          the late 70's showed that infact
                                                                photochemical damage is the
                        Continuous wave lasers can give         mechanism by which visible light,
                        exposures from a few milliseconds       particularly short wavelength blue
                        to several minutes. Q-switched          light, causes injury to the retina of
                        lasers have an exposure time of less    the unaided eye. Data on the
                        than 100ns and produce shock            exposures necessary to produce
                        waves to the eye.IR pulsed lasers       burns on retinal tissue come from
                        pose greatest threat to sight being     studies of victims of the atomic
                        of very short duration(less than 1ms)   explosions at the end of World War
                        with the IR radiation being invisible   Two and about this time an
                        to the eye and the damage often not     ophthalmologist called Meyer-
                        felt as pain.                           Schwickerath began to investigate
                                                                how photocoagulation might be
                        BACKGROUND                              used therapeutically for some
                        The history of science in general,      retinal pathologies.
                        and medicine in particular, is
                        replete with those serendipitous        Using the sun as his light source, he
                        moments when an important new           induced chorioretinal burns around
                        discovery precipitates a flood of       retinal holes in the first successful
                        solutions to old problems and           attempt to prevent a retinal
                        assuming a life of its own, generates   detachment in 1949.
                        a host of applications to other
                        problems as well.                       In the early 50's commercial efforts
                                                                were made to extend such

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techniques throughout ophthalmo-            and cataract. Other lasers, such as
logy with the production of the Zeiss       the carbon dioxide, tunable dye
photocoagulator using a high                and excimer lasers, currently enjoy
pressure xenon-gas source to                fewer applications.
generate the most intense,
controlled, man-made source                 The purpose of this paper is to
available at this time.                     review briefly the characteristics of
                                            these lasers and to illustrate their
Meyer-Schwickerath was probably             more common uses in ophthalmo-
the first clinician to treat closed-        logy.
angle glaucoma in the mid 50's by
this technique. Xenon sources were          Laser Characteristics
not ideal for many reasons. In spite        Lasers are classified according to
of the relatively high intensity of the     the medium used to generate them:
beam which could be generated, it           solid, gas, semiconductor etc.
still requires up to 1.5 seconds to         What makes them powerful and
produce an acceptable burn and              precise is that (a) their light rays
because of the pain, the patient            travel in a parallel fashion; (b) they
would typically move his eye; a             are directional and do not scatter
retrobulbar anaesthetic was thus            like those of a flashlight or
needed. The beam projected was              incandescent light; and (c) they
too wide for optimum manipu-                contain a single wavelength (color).
                                            Light and heat energies travel in
One of these moments in                     waves which have specific
ophthalmology occurred in 1960,             wavelengths and frequencies. The
when T.H.Maiman discovered the              range of waves that we can see –
ruby laser.                                 the visible spectrum – is a very small
                                            part of the entire electromagnetic
Although this laser was used on a           spectrum. Each laser has a specific
limited basis because of technical          wavelength which gives it a specific
factors (instability of the beam and        color and temperature. Lasers can
inconvenient pulse duration),               be infrared, ultraviolet, or of a
subsequent generations of new               visible color, depending on what
lasers, such as the argon, krypton          wavelength is needed to
and neodymium (Nd):YAG (yttrium-            accomplish their purpose. The
aluminum-garnet) lasers, have               longer the wavelength, the slower
made it possible to treat effectively       the frequency, and vice versa. The
the four commonest causes of                special feature of lasers that makes
blindness in the United States:             them so effective is coherence, both
diabetic retinopathy, age-related           spatial and temporal. Spatial
macular degeneration,glaucoma               coherence allows precise focusing

April to June, 2011   INDEPENDENT         REVIEWS                                    307
      of the laser beam to widths as small           higher energy laser light is
      as a few microns, while temporal               absorbed by the target tissue,
      coherence allows selection of                  resulting in vaporization of both
      monochromatic wavelengths within               intracellular and extracellular
      a single laser or a family of lasers.          water. When the local store of water
      The practical implication of spatial           is vaporized, photocarbonization
      coherence, therefore, is that                  occurs.
      extremely small burns to pathologic
      tissue can be made with minimal                The advantage of this type of tissue
      disturbance to surrounding normal              response is that adjacent blood
      tissue. Temporal coherence, on the             vessels are also treated, resulting in
      other hand, allows treatment of                a bloodless surgical field. The
      specific tissue sites by selecting             carbon dioxide laser, with its
      laser wavelengths that are                     wavelength in the far infrared, uses
      preferentially absorbed by these               this method of action and is used
      tissue sites.                                  primarily for bloodless incisions.

      Laser-tissue interactions                      Photochemical effects
      Laser-tissue interactions can occur            Photo-chemical effects include
      in several ways, depending on the              photoradiation and photoablation.
      p o w e r, p u l s e - d u r a t i o n a n d   In the former, intravenous
      wavelength indices chosen.                     administration of hematoporphyrin
                                                     derivative, which is taken up by the
      They are broadly grouped under                 target tissue, causes sensitization of
      photothermal, photochemical and                the target tissue. Exposure of this
      photoionizing effects.                         sensitized tissue to red laser light
                                                     induces the formation of cytotoxic
      Photothermal effects include                   free radicals. Tunable dye lasers are
      photocoagulation and photova-                  used for this purpose.
                                                     Photoablation occurs when high-
      In the first instance, absorption of           energy laser wavelengths in the far
      light by the target tissue results in a        ultraviolet ( < 350 nm) region of the
      temperature rise, which causes                 spectrum are used to break long-
      denaturization of proteins.                    chain tissue polymers into smaller
                                                     volatile fragments. In contrast to the
      Typically, argon and krypton lasers,           photoradiation effect, where
      with wavelengths in the visible                relatively long exposure times
      spectrum, are used in photocoa-                (minutes) are necessary to produce
      gulationand cautery.                           the cytotoxic free radicals, the
                                                     exposure times in the photoablation
      Photovaporization occurs when                  process must be much shorter

308                                        INDEPENDENT       REVIEWS      April to June, 2011
(nanoseconds) compared with              !          Conservation of paintings
diffusion times necessary for heat       !          Paint Removal
conduction into surrounding tissue       !         Remote sensing
(milliseconds). Excimer lasers,          !         Surveying and Range
using this mechanism of action, are                finding
being used experimentally to             !         Material processing
produce precise cuts in corneas.         !         Alignment of pipes and
and to disrupt intravitreal                        structures
membranes.                               !         Engraving of metalseg,
                                                   numbers or scales or
Photoionization effects                            threads to brittle materials
Photoionization occurs when high-        !         General surgery
energy light is deposited over a         !         Micro electronics
short interval to target tissue,         !         Monitoring pollution levels
stripping electrons from the                       in environment
molecules of that tissue. This cloud     !          Meterological applications
of electrons and ionized molecules       !         Communications and
constitutes a "plasma," which then                 warfare
rapidly expands, causing an
acoustic shock wave that disrupts        Clinical Uses of Lasers in
the treated tissue. The ND:YAG           Ophthalmology
laser uses this "photodisruptive"        An increased understanding of
mechanism in lysing secondary            l a s e r- t i s s u e i n t e r a c t i o n s i n
cataract membranes and vitreous          ophthalmology has led to the use of
membranes.                               lasers in treating a wide spectrum of
                                         diseases involving both the anterior
Judicious selection of wavelength,       and posterior segments of the eye.
power and pulse-duration, as well        These diseases include the four
as an understanding of the tissue        commonest causes of blindness in
absorption characteristics, will         the United States:
optimize the clinical use for which
the laser is intended. These are the     Diabetic retinopathy, age-related
goals of current laser research,         macular degeneration, glaucoma
especially for the newer generation      and cataract. As knowledge of the
of lasers, such as the Nd:YAG and        operating characteristics and
excimer lasers.                          treatment limitations of lasers
                                         increases, the use of lasers in the
Some Non-Ophthalmic Uses of              treatment of other ophthalmologic
Lasers                                   problems will be broadened.
!      M i c r o -We l d i n g a n d
       welding to ships, aircraft,       CORNEA
       cars                              Corneal laser surgery with the

April to June, 2011   INDEPENDENT      REVIEWS                                                309
                             modern excimer laser is known to                myopic corrections if more than – 6
                             be the most frequently applied laser            D.In this procedure as compared to
                             procedure in medicine. The                      PRK there is less pain and early
                             interaction between corneal tissue              visual rehabilitation.
                             and the excimer laser was first
                             investigated in 1981 by Taboada,                In the recent years, a new method
                             who studied the response of the                 has been developed and used. This
                             epithelium to the argon fluoride                is called laser subepithelial
                             (AF) and krypton fluoride (KrF)                 keratectomy (LASEK). In this
                             excimer laser. The use of lasers to             procedure, the epithelial layer is
                             reshape the anterior corneal                    completely removed, but about
                             curvature to correct refractive errors          900 of the circumference is allowed
                             has become an established clinical              to remain as a short of hinge. After
                             procedure. Surgical techniques                  the laser treatment, which is
                             such as photorefractive                         equivalent to PRK, the epithelium is
                             keratectomy (PRK) and laser in-situ             replaced.
                             keratomileusis (LASIK) are used to
                             correct optical aberrations of the              Laser thermal Keraoplasty(LTK) with
                             eye, such as myopia or hyperopia,               a Holmium Laser can correct low
                             as well as astigmatism. During PRK              hypermetropia.Laser burns are
                             for the correction of myopia, direct            placed in one or two rings in the
                             flattening is achieved by the                   periphery.The resultant thermally
                             removal of a convex-concave                     induced stromal shrinkage is
                             lenticule of tissue from the outer              accompanied by increase in central
                             surface of the central cornea.                  corneal curvature.
                             Clinical studies determined
                             refractive success rates of between             KERATOCONUS
                             80 and 95% for corrections up to                Keratoconus is a no inflammatory
                             –6 D of myopia.                                 ectasia of the cornea. In general,
                                                                             keratoconus affects both eyes and
  LASIK Refractive Surgery
                             A modification of this technique i.e            leads to a progressive irregular
                             LASIK involves the microkeratome                deformation of the cornea caused
                             to make a lamellar flap (average                by reduced stiffness of the corneal
                             thickness,       of anterior corneal            rigidity. This corneal deformation
                             stroma, followed by refractive                  goes together with a drastic
                             ablation of the exposed stromal                 impairmement of vision ability.
                             bed. This flap is then repositioned             UV crosslinking of the cornea
                             on the exposed stroma, and good                 represents a new treatment method
                             adhesion is usually obtained                    based on molecular cross-linking of
                             without the need for sutures. This              corneal collagen. The biomechani-
                             p r o c e d ur e w a s p a r t i c ul a r l y   cal properties of the cornea are
                             investiga ted in eyes needing high              primarily determined by the

310                                                               INDEPENDENT      REVIEWS      April to June, 2011
 collagen fibers and the degree of         solution is applied onto the cornea
 interfibrillar linkage. The treatment     during 10 to 15 minutes. Next, the
 technique involves the use of UV          cornea will be irradiated during 30
 light and riboflavin (vitamin B2, a       minutes with UV light (365 nm).
 non toxic photosensitizing solution)      During the irradiation, a drop of
 for inducing cross-linking to             serum physiologique is applied
 increase biomedical rigidity of the       every 2 minutes to irrigate the
 cornea. This allows, in case of           cornea.
 keratoconus, to slow down or even
 to stop the progressive thinnening        CATARACT
 of the cornea.                            Laser Capsulotomy
                                           One technique of cataract
 The aim of the uv cross-linking           extraction is a "planned
 treatment is to rise the                  extracapsular extraction" with or
 biomechanical and biochemical             without placement of an intraocular
 stability of the tissues;                 lens within the eye. In this
 biomechanical by increasing the           technique, the anterior capsule of
 interfibrillar linkages of the            the lens is surgically removed,
 collagen and biochemical by               along with the nucleus and cortex of
 increasing the resistance to              the lens, leaving intact the posterior
 enzymatic digestion. The treatment        capsule of the lens. Of the patients
 allows stabilizing and solidifier the     who have undergone the
 cornea, intends to postpone the           procedure, a significant proportion
 point of time where corneal               will have opacification of the
 transplantation becomes necessary         posterior capsule, with resulting
 in patients with keratoconus, and in      loss of vision. The usual surgical
 some cases, even to avoid                 procedure for correcting this
 surgery.The UV cross linking              condition is to incise the capsule
 treatment could also be useful for        with a thin knife or to remove the
 the treatment of iatrogenic               capsule with a vitrectomy cutter.
 keractectasia, a rare complication        However, as an outpatient pro-
 after LASIK.                              cedure, noninvasive capsulotomy
                                           can be done with the Nd:YAG laser,
 PROCEDURE                                 immediately restoring vision. This is
 The procedure takes place                 accomplished by photodisruption
 ambulatory and takes about 45             of the capsule by an expanding
 minutes and the anesthesia consists       shock-wave of the plasma, which is
 of drops. At first, the epithelium of     generated by the laser. With
 the cornea (thin surface layer) will      inaccurate positioning of the laser
 be abrased, in order to allow             light, damage to the cornea, iris,
 penetration of riboflavin into the        intraocular lens and retina may
 corneal stroma. The riboflavin            occur but is extremely rare. Same

April to June, 2011   INDEPENDENT        REVIEWS                                    311
      types complications can occur in         therapy alone is Insufficient in
      Phacoemulsification in Which both        controlling intraocular pressure, for
      anterior and posterior capsular          those patients who have contrain-
      thickening can occur causing             dications to glaucoma medications
      impairment of vision. Both can be        or, for any reason, are unable to use
      treated by Nd:YAG laser.                 eye drops.

      Glaucoma                                 The most common glaucoma laser
      Glaucoma is a group of diseases          procedure is laser peripheral
      affecting the optic nerve that results   iridotomy (PI).
      in vision loss and is frequently
      characterized by raised intraocular      A laser iridotomy(PI) is performed
      pressure (IOP). Its main types are       for patients with narrow angles,
      •       Open angle (chronic)             acute angle closure glaucoma, in
              glaucoma                         the fellow eye of a patient with acute
      •       Angle closure (acute)            or chronic primary angle closure, or
              glaucoma                         pupillary-block glaucoma. Laser
      •       Congenital glaucoma              peripheral iridotomy involves
      •       Secondary glaucoma               creating a tiny opening in the
                                               peripheral iris, allowing aqueous
      Lasers in glaucoma can be used for       fluid to flow from behind the iris
      both diagnostic and therapeutic          directly to the anterior chamber of
      purposes.                                the eye. This typically results in
                                               resolution of the forwardly bowed
      1. Diagnostic                            iris and thereby an opening up of
      (a); The Heidelberg retinal              the angle of the eye. There are two
      topograph(HRT) is confocal laser         types of lasers in use today -
      scanning microscope designed for         Nd:YAG Q-switched laser (2 – 8
      three-dimensional imaging of             mJ) or argon laser (800 – 1000
      posterior segment of eye like            mW). Argon laser began to replace
      evaluation of optic nerve head in        surgical iridotomy as a safer, non-
      glaucoma.                                invasive method of making an
                                               iridotomy in the late 1970s. It was
      (b); Scanning Laser polarimetry (the     demonstrated to be safe and
      nerve fiber analyzer) give               effective, but required melanin for
      assessment of retinal nerve fibers       tissue absorption of the energy,
      thickness that is decrease as            making it less easy to penetrate
      glaucoma progress.                       lightly pigmented blue irides. The
                                               Nd:YAG laser replaced argon as
      2. Therapeutic                           the most common means of
      Glaucoma laser treatment is often        performing LPI in the late 1980s.
      recommended when medical

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 The Q-switched mode of the                The eye is not dilated for this
 Nd:YAG laser causes                       procedure, so that there is a clear
 photodisruption of tissues by the         view into the angle. A gonioscopy
 formation of a high energy ionic          lens is placed on the anesthetized
 plasma at the location of focus of        cornea and a slit lamp
 very intense energy. It has the           biomicroscope is used to aim the
 advantage of not requiring the            laser beam into the angle by
 presence of melanin pigment for iris      reflection on one of the gonio
 absorption.                               mirrors. The complete circle of the
                                           angle (360 degrees) is available for
 Complications of laser iridotomy          treatment. Treatment of half the
 include, irritation, blurred vision,      angle (180 degrees) may be done
 iritis, iris hemorrhage, elevated         in one session in order to judge the
 intraocular pressure, corneal injury      response of the eye before the other
 or retinal burns.                         half is done on another day. The ALT
                                           treatment can only be repeated one
 Argon laser trabeculoplasty (ALT) is      time. The patient typically will still
 a procedure which has been proven         need to use drops
 to be efficacious for different types
 of open angle glaucoma: primary           LASER IRIDOTOMY
 open angle glaucoma, pseudoex-            to control the IOP   .Modification of
 foliation glaucoma and pigment            this procedure is selective laser
 dispersion glaucoma. Patients with        trabeculoplasty (SLT) performed
 poor medical compliance can               with a Q-switched 532 Nd:YAG
 benefit from ALT before other             laser. SLT works by using a specific
                                                                                    LASER IRIDOTOMY
 surgical intervention is considered.      wavelength to irradiate and target
                                           only the melanin-containing cells in
 In the ALT procedure, the eye             the trabecular meshwork, without
 surgeon directs a laser beam into         incurring collateral thermal
 the trabecular meshwork, which is         damage to adjacent non-
 the primary aqueous (fluid)               pigmented trabecular meshwork
 drainage region of the eye. In most       cells and underlying trabecular
 cases, 180 up to 360 degrees of           beams. The laser beam bypasses
 the trabecular meshwork is treated        surrounding tissue leaving it
 with laser spots, which typically         undamaged by light. This is why,
 requires about 40 to 80 laser             unlike ALT, SLT is repeatable several
 applications. The effect of the           times. Indications for this procedure
 procedure is increased drainage of        and complications (intermittent
 aqueous fluid out of the eye and          intraocular pressure elevation, iritis
 intraocular pressure reduction to         or heamorrhage) are similar like in
 20 – 25%. Efficacy of the ALT             ALT.
 procedure lasts for about 5 years.

April to June, 2011   INDEPENDENT        REVIEWS                                                      313
      Another glaucoma laser procedure        and the unpredictability of the
      is argon laser peripheral iridoplasty   amount of IOP reduction, these
      (ALPI). ALPI is a method of opening     procedures are usually reserved for
      an appositionally closed angle in       the following conditions: eyes with
      situations in which laser iridotomy     glaucoma refractory to other forms
      either cannot be performed or does      of surgical or medicinal therapy,
      not eliminate appositional angle-       eyes with poor visual potential,
      closure because mechanisms other        neovascular glaucoma, traumatic
      than pupillary block are present.       glaucoma, aphakic and
      The procedure consists of placing       pseudophakic glaucoma, chronic
      contraction burns of low power,         partial or total angle-closure
      long duration, and large spot size in   glaucoma, aniridia or iridocorneal
      the extreme iris periphery to           endothelial syndrome.
      contract the iris stroma between the
      site of the burn and the angle,         Endo-laser Cyclophoto-
      physically pulling open the angle.      coagulation: A laser can be used
      ALPI is recommended in plateau iris     within the eye, usually in
      syndrome, or angle closure              conjunction with another surgery, to
      glaucoma. The argon laser is set to     destroy the ciliary body.
      produce contraction burns (500 μm
      spot size, 0.5 to 0.7 second            RETINA
      duration, and, 200-400 mW               Light coagulation and laser
      power).                                 treatment of the retina were
                                              introduced to ophthalmology
      Cyclodestructive procedures in          around middle of the last century.
      glaucoma lower the intraocular          They are widely used for the
      pressure (IOP) by reducing              treatment of diabetic retinopathy
      aqueous inflow as a result of           and other ischemic retinopathies.
      distruction ciliary processes. The      Retinal laser photocoagulation
      use of light energy to ablate the       improves inner retinal oxygenation,
      ciliary body was first proposed by      which affects retinopathy through
      Weekers and co-workers (21) in          the relief of hypoxia and
      1961 using xenon arc photo-             consequent change in growth
      coagulation In 1972 Beckman and         factor production and hemo-
      Waeltermann (2) performed the first     dynamics.
      trans-scleral cyclophoto-
      coagulation (TSCPC) procedure           Diabetic retinopathy, branch vein
      with the ruby laser. Since then, the    occlusion, central vein occlusion
      neodymium (Nd):YAG and diode            and sickle cell retinopathy are the
      lasers have been used for               most common retinal neovascular
      transscleral cyclophotodestruction.     diseases encountered by an
      Due to the high complications rate,     ophthalmologist. The underlying

314                                  INDEPENDENT     REVIEWS      April to June, 2011
pathophysiologic mechanism                  retinopathy. The pattern of macular
common to these entities is a vaso-         edema may fall into one of three
occlusive phenomenon occurring              categories: focal (circinate), diffuse
on the venous side of the circulation       or cystoid. In the first instance, the
in diabetic retinopathy and the vein        source of leakage is located and,
occlusions and on the anterior side         after cauterization or photo-
of the circulation in sickle cell           coagulation, the edema resolves
retinopathy. In each instance,              and visual acuity is improved . The
nonperfusion of the retina leads to         efficacy of argon or krypton laser
tissue hypoxia. It is believed that, as     photocoagulation in treating
a consequence of this, the hypoxic          diffuse or cystoid macular edema,
retina liberates an angiogenesis            however, is less defined but is
factor, which stimulates the                currently being investigated within
formation of neovascular tissue,            the Early Treatment Diabetic
usually at the junction of perfused         Retinopathy Study being conducted
and nonperfused retina. The                 by the National Eye Institute. In the
treatment of this neovascular               later stages of nonproliferative
proliferation is to destroy the             diabetic retinopathy, endothelial
hypoxic retina so that most of the          proliferation leads to closure of the
stimulus for neovascularization is          capillary lumens, resulting in
reduced or eliminated. This type of         capillary nonperfusion and hypoxia
laser treatment is called panretinal        of areas of the retina usually served
photocoagulation.                           by these capillaries. It is felt that
                                            these hypoxic areas of the retina
Diabetic retinopathy is a leading           initiate the release of an angiogenic
cause of visual loss in industrialized      factor, which stimulates the
countries. Diabetic retinopathy is          formation of neovascular tissue,
primarily a disease of the retinal          usually at the junction of perfused
capillaries. The earliest pathologic        and nonperfused retina on the optic
changes in these capillaries are loss       nerve head and in certain cases, on
of the tight junctions of the               the surface of the iris (rubeosis iridis)
endothelial cells and formation of          and the trabecular meshwork.
microaneurysms within the vessel
walls. Leakage of serum,                    These developments are part of the
erythrocytes or both into the retinal       complex called proliferative
interstitium takes place. If this           diabetic retinopathy. If left
occurs near the posterior pole,             untreated, retinal neovascular
macular edema results, with                 tissue will grow on the adjacent
concomitantly reduced visual                vitreous cortex. As the cortex
acuity. These early changes are part        retracts or exerts traction on these
of the complex called background            abnormal blood vessels, vitreous
or nonproliferative diabetic                hemorrhages of varying severity will

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                                      o c c u r. S i m i l a r l y, u n t r e a t e d   Retinal vein occlusion (RVO)
                                      neovascularization of the                         It is a common retinal vascular
                                      trabecular meshwork in the anterior               disorder that frequently is
                                      chamber of the eye can lead to                    associated with severe visual loss.
                                      neovascular glaucoma.                             There are two forms of retinal vein
                                                                                        occlusion, branch retinal vein
                                      Diabetic retinopathy classification               occlusion (BRVO) and central
 Prolefrative Diabetic Retinopathy
                                      includes preclinical, nonpro-                     retinal vein occlusion (CRVO). A
                                      liferative (mild, moderate, and                   branch retinal vein occlusion is
                                      severe or preproliferative diabetic               essentially a blockage of the
                                      retinopathy) and proliferative                    portion of the circulation that drains
                                      stages (low risk, high risk, and                  the retina of blood. Central retinal
                                      advanced). Diabetic maculopathy                   vein occlusion is closure of the final
                                      (exudative, edema-tous, or                        retinal vein (located at the optic
                                      ischemic) may be associated with                  nerve) which collects all of the
 Resolution of Abnormal vessels       either nonproli-ferative or                       blood after it passes through the
 After Laser therapy in proliferate
        diabetic retinopathy
                                      proliferative retinopathy. Prevention             capillaries. There is presently no
                                      requires the tightest possible control            effective treatment available to
                                      of both blood glucose and blood                   prevent or restore the visual loss
                                      pressure. Laser photocoagulation                  from acute CRVO.
                                      remains the only procedure
                                      recommended for severe                            Following a vein occlusion, the
                                      nonproliferative or proliferative                 primary concern is to treat the
                                      retinopathy and maculopathy. The                  secondary complications: macular
                                      Diabetic Retinopathy Study (DRS)                  edema, macular ischemia (non-
                                      showed that the rate of severe visual             perfusion) and neovacularization
                                      loss in high-risk proliferative                   (growth of new abnormal blood
                                      diabetic retinopathy could be                     vessels). Argon or diode laser
                                      reduced by as much as 60%                         treatment may be useful in
                                      following the timely application of               managing these complications.
                                      panretinal laser photocoagulation                 One type of laser treatment, focal
                                      therapy. Results from the Early                   laser, can be used to close off areas
                                      Treatment Diabetic Retinopathy                    of leakage from the blood vessels
                                      Study (ETDRS) demonstrated that                   that cause macular edema.
                                      focal laser photocoagulation                      Another type of laser treatment,
                                      treatment to the macula region                    panretinal photocoagulation, can
                                      could substantially reduce the risk               cause neovascularization to regress
                                      of visual acuity loss in patients with            by making the retina less starved for
                                      clinically significant diabetic                   oxygen.
                                      macular edema.

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Age-related macular                      damage to the surrounding tissues,
degeneration                             such as photoreceptors or retinal
Nowadays, laser treatment is also        pigment epithelium (RPE). In PDT, a
available in the age-related             photosensitizer, Verteporfin is
macular degeneration (AMD), a            administered intravenously and
disease of our civilization. Macular     allowed to perfuse the CNV, as well
degeneration is a progressive eye        as the remainder of the body.
condition affecting the central
vision and causing irreversible          Fifteen minutes after the start of
blindness in people over the age of      intravenous infusion, the
50.                                      verteporfin is activated by a red
                                         laser of a specific wavelength
AMD has two basic forms                  (689nm). The non-thermal laser
(Dry and Exudative)                      light activates the verteporfin
Dry AMD accounts for about 90%           producing the singlet oxygen that
of cases, is the milder form of the      both coagulates and reduces the
disorder. Exsudative AMD is the          growth of abnormal blood vessels.
much more visually debilitating          This, in turn, inhibits the leakage of
form of macular degeneration,            fluid from the CNV.
often accompanied by choroidal
neovascular membranes, which are         Intraocular tumors
the leaky vascular structures under      The first attempts to treat
the retina. There are two basic          intraocular tumors by means of
forms of laser treatment for             photocoagulation were carried out
exsudative AMD: conventional             in the late 1950s by G. Meyer-
argon or diode laser therapy and         Schwickerath with the xenon arc
the recently approved                    photocoagulator.
photodynamic therapy (PDT).
                                         Nowadays, lasers are an
Conventional laser burns the             irreplaceable tool in the manage-
abnormal blood vessels and thus          ment of malignant and benign
stops the leakage. However, since it     intraocular lesions.
also damages the normal retina
structures, it may itself lead to         Transpupillary thermotherapy (TTT)
decreased vision. Hence, it is           using an 810nm infrared laser has
suitable only in selected cases          become one of the most popular
where the new vessels are not very       treatment for small melanomas.
close to the central macular area.       Lasers can be also used as an
The concept of the new treatment         adjunctive tool in combination with
for exsudative AMD is the closure of     other treatment modalities in
subretinal choroidal neovasculari-       therapy regimens for medium or
zation (CNV) without significant         even large melanomas. The main

April to June, 2011   INDEPENDENT      REVIEWS                                    317
      advantages of laser treatment            In eyelids they are used for
      compared to other modalities like        treatment of misdirected eyelashes
      irradiation are the broad                (Triachiasis), small size benign and
      availability, the relatively easy        malignant eyelids tumors.
      performance and thus
      reproducibility, the high precision      Lacrimal Drainage System;
      during the treatment and the safety      LASER can be used for treatment of
      for the adjacent tissues.                blocked punctum (punctoplasty) as
                                               well as Endolaser-DCR is done with
      Retinal detachment;                      Holmium: YAG under local
      Laser photocoagulation is also           anesthesia in elderly patients who
      mainly used in the retina                have complaint of epiphora.
      abnormalities such as: tears,
      breaks, holes, lattice degeneration      Advantages of laser therapy.
      or retinoschisis, which predispose       !    Less pain, bleeding,
      to a rhegmatogenous retinal                   swelling, and scarring.
      detachment. With argon laser             !    W i t h l a s e r t h e r a p y,
      photocoagulation a thermal burn is            operations are usually
      created to surround the lesion and            shorter.
      any subretinal fluid associated with     !    In fact, laser therapy can
      it. The burn becomes an adhesion              often be done on an
      between the retina and retinal                outpatient basis.
      pigment epithelium, and this limits
      potential flow of fluid from the         Disadvantages of laser therapy.
      vitreous cavity through a break thus     !     Laser therapy is expensive
      preventing retinal detachment.                 and requires bulk
      Current investigative work is under
      way on the use of the Nd:YAG and         !      In addition, the effects of
      excimer lasers in lysing vitreoretinal          laser therapy may not last
      bands.                                          long, so doctors may have
                                                      to repeat the treatment for a
                                                      patient to get the full benefit.

318                                   INDEPENDENT     REVIEWS       April to June, 2011
REFFRANCES                                             6.      Lai JS, Tham CC, Chua JK, Poon
1.      Awan MA, Tarin S.A. Review of                          AS, Lam DS. Laser peripheral
        photodynamic therapy. Surgeon                          iridoplasty as initial treatment of
        2006; 4(4): 231-6.                                     acute attack of primary angle-
2.      Camellin M. Subepithelial                              closure: A long-term follow- up
        corneal ablation. Ocular Surgery                       study. J Glaucoma 2002; 11:
        News International Edition 1999;                       484-487.
        3:14                                           7.      Porta M, Allione A. Current
3.      E a r l y Tr e a t m e n t D i a b e t i c             approaches and perspectives in
        Retinopathy Study Group:                               the medical treatment of diabetic
        Photocoagulation for diabetic                          retinopathy. Pharmacol Ther.
        macular edema: ETDRS report                            2004 Aug;103(2):167-77.
        number 1. Arch Ophthalmol                      8.      Ritch, R, Tham CC, Lam DS. Long
        985; 103:1796-1806                                     term success of argon laser
4.      Friedman DS, Nordstrom B,                              peripheral iridoplasty in the
        Mozaffari E, Qiugley HA.                               management of plateau iris
        Variations in treatment among                          syndrome. Ophthalmology
        adult-onset open-angle                                 2004; 111(1): 104-108.
        glaucoma patients.                             9.      Seiler T, McDonnell PJ. Excimer
        Ophthalmology 2005; 112(9):                            laser photorefractive keratec-
        1494-9.                                                tomy. Syrv Ophthalmol 1995; 40:
5.      Holz HA, Lim MC. Glaucoma                              89-118.
        lasers: a review of the newer                  12.     Kanski JJ.Clinical ophthalmo-
        techniques. Curr Opin                                  logy.5th ED.London.Butterworth&
        Ophthalmol. 2005 Apr;                                  Heinmann 2003;27-53.

                                                                                                     The author :
                                                                                                     Faheem Ahmad
                                                                                                     is Assistant Professor of
                                                                                                     Ophthalmology at
                                                                                                     Independent Medical
                                                                                                     College Faisalabad.

April to June, 2011      INDEPENDENT                 REVIEWS                                                                     319

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