Dr.Ali.A.Taqi 5th year students

1
Dr.Ali.A.Taqi5th year students

• LASER IN OPHTHALMOLOGY
• REFRACTIVE SURGERY

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.

3
Basic LASER
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

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

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.
8
LASER USED IN OPHTHALMOLOGY

• 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.

9
RETINAL PHOTOCOAGULATION

• Factors in retinal photocoagulation

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.

11
(No Transcript)
12
(No Transcript)
13
A. NVD and a small vitreous hemorrhage.
Panretinal photocoagulation was given. B. Two
months later, the NVD has completely regressed.
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.

15
(No Transcript)
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.

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 (NdYAG)
  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.

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

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.

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.
•  

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.

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.

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

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

26
Complications of LASIK
27
(No Transcript)
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).

29
Aiming beam lasers and hand held pointers
30
(No Transcript)
31
Laser Pointer Safety Tips

• Tip 1 Dont Use Laser Pointers Without Labels
• Tip 2 Dont Point Laser Beams at Faces or Eyes
• Tip 3 Dont Point Laser Pointers at Aircraft
• Tip 4 Dont Point Laser Pointers at Automobiles
• Tip 5 Dont Hold a Laser Beam on the Skin
• Tip 6 Dont Point at Unidentified Objects when
  Astronomy Pointing
• Tip 7 Dont Point Lasers at Animals for Any
  Reason
• Tip 8 Dont Give Laser Pointers to Children

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.

33
(No Transcript)
34
Intrastromal Corneal Ring Segments (INTACS)

• The polymethylmethacrylate ring segments

35
(No Transcript)
36
References.

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