2.3. Laser effect

management of ROP, the golden standard of treatment in ROP remains the laser photocoagula-

In order to understand the rationale of laser treatment in ROP and its mechanism of action, the pathogenesis of ROP is summarized, as well as its classification and indications for treatment. Practical considerations on indirect diode laser photocoagulation for ROP are presented

Vasculogenesis and angiogenesis are two distinct terms that need to be explained. In the vasculogenesis process, the origin of blood vessels is represented by the endothelial progenitor cells that coalesce and form lumen and vasculogenic networks. In the angiogenesis process, the

ROP is a biphasic disease directly related to the saturation of oxygen, which is administered in order to maintain the prematurely born vital functions. Phase 1 (between 22 and 30 weeks PCA) is characterized by relative hyperoxia and decreased vascular endothelial growth factors (VEGF) levels. The consequence of this situation is delayed vessel formation. Phase 2 (between 31 and 44 weeks PCA) is defined by relative hypoxia and increased VEGF levels, having as

The cause of ROP is the non-development of retinal vessels with subsequent retinal ischemia

Screening for ROP is essential for reducing the blindness rate related to this disease [3]. It should be made by indirect ophthalmoscopy by specially trained ophthalmologists according

In classifying ROP, the following criteria are used: zone, stage and the presence/absence of "plus" disease. The retina is divided into three zones and 12 clock hours. Zone 1 corresponds to a circle having the radius equal to the double distance between the optic disc and the fovea. Zone 2 describes a circle with the radius that equals the distance between the optic disc and the nasal ora serrata. Zone 3 is the remaining "crescent" of retina in the temporal area [3, 4].

Stages are defined according to the modifications at the limit between the vascularized and nonvascularized retina. Stage 0 reflects no modification at this level, but the retinal vascularization is not yet completed. In stage 1, a demarcation line (within the retinal plane) is identified at this site. In stage 2, there is a non-vascularized, white ridge (elevated from the retinal plane) at the limit between the two retinal regions, and in stage 3, the ridge is vascularized, red. Stage 4a corresponds to peripheral retinal detachment. In stage 4b, the fovea is also detached, and in stage 5,

2. Indirect diode laser photocoagulation in the treatment of ROP

new vessels form from the existing ones by vascular sprouting [2].

tion of the non-vascularized retina [1].

108 Laser Technology and its Applications

subsequently.

2.1. Pathogenesis of ROP

consequence uncontrolled vessel growth.

to criteria which are specific to each country/region.

there is total retinal detachment in an open or closed funnel [3, 4].

and new vessel proliferation [2].

2.2. ROP classification

Understanding laser technology starts from the translation of the word LASER: light amplification by the stimulated emission of radiation.

Atoms occupy various energetic levels. Lower energetic levels are associated with higher stability. If the atom absorbs energy under the shape of a photon, it "jumps" on a higher energetic level in a state of excitation. The excited atom can "fall" back spontaneously on the lower energetic level by emitting a photon. The excited atom can be "forced" to fall from the higher on the lower energetic level if it meets a photon carrying the energy equal to the difference between the two levels. This process is called stimulated emission: a photon stimulates the emission of another photon [5].

If we would be able to bring the majority of atoms on the superior energetic level, the incident radiation will induce the emission of a more intense beam than the incident one. This is called radiation amplifying. The key problem is to obtain a state with more atoms on the superior energetic level, which is called population inversion and is reached by pumping. In order to amplify the light, the system is closed between two parallel mirrors forming a cavity. The mirrors allow photons to jump back and forth by continuously reflecting between them, thus producing stimulated emissions. When the radiation flux becomes extremely intense, it is allowed to get out of the cavity as laser beam [5].

The abovementioned principles explain the key properties of the laser radiation:


These properties offer theoretical advantages to the laser radiation over the white light that are translated by its clinical applications in various ocular diseases [5].

Monochromatic laser light allows the specific selection of a wavelength that is going to be absorbed by a specific pigment in the eye according to the ocular condition.

Photocoagulation also eliminates the photoreceptor cells, which are high oxygen consumers,

Indirect Diode Laser in the Treatment of Retinopathy of Prematurity

http://dx.doi.org/10.5772/intechopen.79828

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A tight adhesion between the retina and choriocapillaris is created following laser photocoag-

Diode laser has an infrared emission (810 nm), and it cools in the environment and has a life span of 30,000 h. The transmission optic system is very simple: it is constituted by mirrors leading the laser beam from the slit lamp to the patient's retina. When attached to the indirect ophthalmoscope, such as in the ROP treatment, this role is taken by a system of fiber optics.

The laser fiber is connected from the laser to the indirect ophthalmoscope, and the laser impacts are delivered by acting on a pedal, which is also connected to the laser. The console allows the operator to choose the adequate parameters of the laser impact: dimension, exposure time and power. The operator wears the helmet throughout the treatment and moves his head in order to deliver the light from the indirect ophthalmoscope and the laser beam into the

The pigmented cells destroyed by laser liberate a substance that inhibits angiogenesis [5].

allowing the use of available oxygen by the viable cells.

2.5. Technical characteristics of the indirect diode laser

ulation, increasing oxygen flow to the retina.

infant's eye (Figure 1).

Figure 1. Indirect diode laser.

Also there is no chromatic aberration allowing the obtainment of a small retinal impact.

Laser light is much more intense, which makes it possible to use low energies to obtain a clinical effect with a significantly lower risk for complications.

Parallelism allows the obtainment of small retinal lesions in the periphery.

Therapeutic energy can be pre-selected by the ophthalmologist according to the effect on the retina: lower energies are used initially which are progressively increased, up to the moment where the desired effect is obtained [5].
