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Presentation on theme: "Dr.Ali.A.Taqi 5 th year students LASER IN OPHTHALMOLOGY & REFRACTIVE SURGERY 1."— Presentation transcript:


2 LASER Is an acronym for the instrument's mode of action: (Light Amplification by the Stimulated Emission of Radiation). Laser light is coherent: all photons, have same wavelength and are in phase. A laser beam is collimated, i.e. the waves of light are parallel. 2

3 Basic LASER 3

4 4 Types of Lasers used in Ophthalmology 1-Argon Laser 2-Diode Laser 3-YAG Laser 4-Excimer Laser What do Lasers do? Laser rays have energy. When they hit the target, they transmit that energy to the target. Heat is also given out. The effects in the eye are a combination of the Laser and heat energy. Some Lasers are used to create holes, e.g. YAG Laser Iridotomy in Glaucoma. The Excimer Laser has cutting power, used in LASIK. The Argon and Diode Lasers are used to create burns that treat Retinal tears and Diabetic Retinopathy (DMR).

5 5 Use of Laser in Ophthalmology Lasers have been used widely in treatment of eye diseases. Such as, 1.Eyelid growths, including lid cancers 2.Trichiasis (Misdirected eye lashes)Trichiasis 3.Open up or block Lacrimal Puncta. 4.Pterygium (Conjunctival degeneration)Pterygium 5.To alter corneal curvature and correct refractive errors as in PRK, LASIK etc. correct refractive errors 6.Glaucoma (Increased eye pressure)Glaucoma 7.To open opacified posterior capsule, about 6 months after cataract surgeryopacified posterior capsule 8.In closing Retinal tears in treatment and prevention of RD.treatment prevention of RD 9.In Diabetic Retinopathy (DMR)DMR 10.For treatment of tumors like Retinoblastoma.Retinoblastoma

6 Effects of the Laser energy on ocular tissues Radiation wavelengths from 400 to 1400 nm can enter the eye and reach the retina. effects of laser energy on ocular tissues depend on:- 1----the wavelength and pulse duration of the laser light 2----the absorption characteristics of the tissue (largely determined by the pigments contained within it). 3----the duration of exposure. When the laser energy exceeds the threshold, causes tissue damage. The effects can be ionizing, thermal or photochemical. 6

7 Laser light can be delivered: 1-along a fiber-optic cable to a slit lamp, 2-an indirect ophthalmoscope, 3-an intraocular endolaser probe. 7

8 1. Argon blue-green gas laser It is a mixture of 70% blue (488 nm) and 30% green(514 nm) light. They are most commonly employed for retinal photocoagulation for trabeculoplasty Photocoagulations aims to treat the outer retina and spare the inner retina to avoid damaging the nerve fiber layer. Argon green (blue screened out) photocoagulation of the macula does not cause direct retinal damage. It is well absorbed by melanin and hemoglobin, but Xanthophyll (in the inner layer of the macula) absorbs blue light (but not green) and thus the use of blue light at the macula is contraindicated in order to avoid, direct damage to the retina. LASER USED IN OPHTHALMOLOGY 8

9 RETINAL PHOTOCOAGULATION Factors in retinal photocoagulation 9

10 Retinal photocoagulation pan photocoagulation for diabetic retinopathy the aim is the elimination of abnormal retinal blood vessels through direct treatment to the blood vessels or destruction of the ischemic areas of the retina. This kind of laser treatment entails marked destruction of retinal tissue. Conversely, application of laser energy in the macular area has to be modified owing to factors present in that area, such as the presence of xanthophyll pigment, the reduced thickness of the retina, the increased density of melanin in retinal pigment epithelium and the inner choroid, and the need to minimize retinal damage to avoid disabling scotomas in the central field of vision. 10

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13 A. NVD and a small vitreous hemorrhage. Panretinal photocoagulation was given. B. Two months later, the NVD has completely regressed. 13

14 Laser trabeculoplasty-SLT Laser trabeculoplasty is probably the most widely employed laser technique for the treatment of glaucoma. It to be effective in approximately two thirds to three fourths of patients with primary open-angle glaucoma. It also is useful in some secondary open-angle glaucomas such as exfoliation syndrome glaucoma and pigmentary glaucoma; in eyes that have had previous filtering surgery; and in eyes that have had surgical or laser iridectomies because of acute angle-closure glaucoma attacks. 14

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16 2. Nd-YAG laser The neodynium-yttrium-aluminum- garnet: laser emits infrared (1064 nm) radiation, it is Continuous wave (C'W) It is commonly used to:- – the posterior capsule of the lens following cataract surgery –the iris (Peripheral Iridotomy) in narrow angle glaucoma. It is emitted from neodynium molecules which are suspended in a clear" YAG crystal to achieve higher concentration ions than is possible in a gas laser medium, wavelength is invisible and requires a He-Ne aiming beam. Before use on a patient's eye, must ensure that the laser beam and the aim focused at the same point. 16

17 Laser iridectomy Laser iridectomy is now the standard surgical treatment of angle-closure glaucoma. Over the past decade, the high-energy, short-duration pulsed lasers, such as the neodymium: yttrium- aluminum-garnet (Nd:YAG) lasers, have achieved preferred status for performing laser iridectomies. There are still some situations, for example, in eyes with uveitis or rubeosis iridis, where the older argon laser techniques still may be preferred. 17

18 Laser iridectomy Indications for Laser Iridectomy 1-Nonperforate surgical iridectomy 2-Acute angle-closure glaucoma 3-Fellow eye of a patient with acute angle-closure glaucoma 4-Chronic angle-closure glaucoma 5-Positive provocative test result 6-Aphakic or pseudophakic pupillary block 7-Uveitis with 360° posterior Synechiae 8-Before a trabeculoplasty to open the angle approach and facilitate treatment 9-Differentiating a pupillary block in aphakia or pseudophakia from ciliovitreal block 18

19 3-The excimer laser. Its name derived from ‘excited dimer' two atoms forming a molecule in the excited state. In clinical use employ an argon-fluorine (Ar-F) dimer laser medium to emit 193 nm ultraviolet (UV) radiation. High absorption of UV by the cornea limits its penetration. Each photon has 6.4 eV, sufficient to break intramolecular bonds. The delivery of a relatively high level of energy to a small volume of tissue causes tissue removal (i.e. ablation) The ablation depth may be precisely determined. temperature in a tiny volume of treated tissue becomes very high, but the amount of heat produced is very small and there is no significant rise in temperature of adjacent tissue. It is therefore ideally suited to (PRK) and (LASIK) to reshape the corneal surface & phototherapeutic keratectomy (PTK) to remove abnormal corneal surface tissue. 19

20 Refractive eye surgery Is any eye surgery used to improve the refractive state of the eye and decrease or eliminate dependency on glasses or contact lenses. This can include various methods of surgical remodeling of the cornea or cataract surgery. The most common methods today use excimer lasers to reshape the curvature of the cornea. Successful refractive eye surgery can reduce or cure common vision disorders such as myopia, hyperopia and astigmatism, as well as degenerative disorders like keratoconus.eye surgeryeyeglassescontact lensescorneacataract surgeryexcimer lasersmyopiahyperopiaastigmatismkeratoconus 20

21 The correction of myopia :- Photorefractive keratectomy (PRK), Laser in situ keratomileusis (LASIK), Intrastromal corneal ring implants, Phakic intraocular lens implants… Clear lens extraction for very high myopia have been gaining acceptance among surgeons and patients as the risks for these procedures decrease. With a good surgical outcome and the improvements in medical technology allowing for high-quality optical devices, these methods of optical correction of myopia are superior to spectacle correction by their reduction or elimination of lens aberrations and by their increase in image size relative to spectacle correction. Obviously, the benefits of these methods of optical correction must be weighed against the risks, the downside of which can be considerable. 21

22 Laser refractive surgery Although refractive errors are most commonly corrected by spectacles or contact lenses, laser surgical correction is gaining popularity. The excimer laser precisely removes part of the superficial stromal tissue from the cornea to modify its shape. Myopia is corrected by flattening the cornea and hypermetropia by steepening it. In photorefractive keratectomy (PRK),the laser is applied to the corneal surface. In laser assisted in situ keratomileusis (LASIK), a hinged partial thickness corneal stromal flap is first created with a rapidly moving automated blade, the flap is lifted and the laser applied onto the stromal bed. Unlike PRK, LASIK provides a near instantaneous improvement in vision with minimal discomfort. Serious complications during flap creation occur rarely. Intraocular lenses can also be placed in the eye but this carries all the risks of intraocular surgery and the possibility of cataract formation. 22

23 LASIK by excimer laser for myopia A. Hinged flap made with microkeratome. B. Laser ablation (shaded area destroyed) of bed to alter curvature. C. Flattened cornea after replacement of flap. Indications : corrects high degrees of myopia ” Laser in situ keratomileusis (LASIK), which combines keratomileusis with the accuracy of the excimer laser, is used worldwide to correct a broad range of refractive abnormalities. The safety and efficacy of the procedure combined with the quick visual recovery and minimal patient discomfort have made LASIK the most popular refractive procedure for the treatment of all but the highest levels of myopia and astigmatism, and low to moderate hyperopia 23

24 (LASIK) technique 1-Thin flap of cornea fashioned 2-Bed treated with excimer laser 3-Flap repositioned 24

25 Photorefractive Keratectomy Photoablation occurs because the cornea has an extremely high absorption coefficient at 193 nm, with a single 193 nm photon having sufficient energy to break carbon-carbon and carbon-nitrogen bonds directly that form the peptide backbone of the corneal collagen molecules. Consequently, excimer laser radiation ruptures the collagen polymer into small fragments, and a discrete volume of corneal tissue is removed with each pulse of the laser 25

26 Complications of LASIK 26

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28  4. Diode lasers  It emit an infrared (wavelength of 810 nm) in continuous wave mode.  It is absorbed only by melanin i.e. why most commonly used for retinal photocoagulation;  low scattering of this wavelength ensures good penetration of the ocular media and of edematous retina. It also penetrates the sclera.  The transparency of sclera to diode laser also allows photocycloablion of the ciliary body in 'end stage glaucoma.  It has been used endoscopically to create a dacriocystorhinostomy (DCR). 28

29 Aiming beam lasers and hand held pointers 29

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31 Laser Pointer Safety Tips Tip 1: Don’t Use Laser Pointers Without Labels Tip 2: Don’t Point Laser Beams at Faces or Eyes Tip 3: Don’t Point Laser Pointers at Aircraft Tip 4: Don’t Point Laser Pointers at Automobiles Tip 5: Don’t Hold a Laser Beam on the Skin Tip 6: Don’t Point at Unidentified Objects when Astronomy Pointing Tip 7: Don’t Point Lasers at Animals for Any Reason Tip 8: Don’t Give Laser Pointers to Children 31

32 Safety Considerations Never look directly into the laser beam. Do not aim the laser at reflective surfaces. Never view a laser pointer using an optical instrument, such as binocular or a microscope. Do not allow children to use laser pointers unless under the supervision of an adult. Use only laser pointers meeting the following criteria –Labeled with FDA certification stating "DANGER: Laser Radiation" for Class 3R lasers or "CAUTION: Laser Radiation" for Class 2 pointers. –Classified as Class 2 or 3R according to the label. Do not use Class 3b or 4 products. –Operates at a wavelength between 630 nm and 680 nm. –Has a maximum output less than 5 mW, the lower the better. 32

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34 Intrastromal Corneal Ring Segments (INTACS) The polymethylmethacrylate ring segments 34

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36 References. Clinical optics,2 ND edition 1997. Wright interactive ophthalmology. By K.Wright,1997 on CD. Duane's ophthalmology,basic science, on CD,2003. Web search for images. 36

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