Ординатура / Офтальмология / Английские материалы / Retinal and Vitreoretinal Diseases and Surgery_Boyd, Cortez, Sabates_2010

vision loss, restriction of the visual fields and nictalopia; however it has been demonstrated that laser is effective at preserving vision in the long run, as compared to no treatment in a scientifically impeccable study of more than 1700 patients.(2)

•For a successful result patients must return for follow-up visits, since additional laser is needed often. Optimization of medical control of glucose, blood pressure and anemia are essential in the care of their disease.

•A handout may be effective in patient’s education.

Lenses

The Goldmann three-mirror lens is seldom used for PRP. However, its high magnification and resolution allows precision laser treatment at the posterior pole and the side mirrors may be used for treatment of specific lesions at the mid periphery or periphery of the retina. The Goldmann lens gives an upright image.

Wide angle lenses are usually employed in PRP. These lenses provide a wider field of view, with an inverted image. Wide-angle lenses differ in image magnification, laser spot magnification factor and field of view (Table 1).

The wider the field of view, the smaller is the image magnification.

Of lenses in Table 1, the Mainster standard is the less appropriate or PRP, given the small field of view 90°, but can be used for treatment at the posterior pole. All other lenses mentioned in Table 1 are quite appropriate for PRP.

The author uses routinely the Mainster Wide-Field for PRP, because of its high resolution. It has a field of view of 118o that can be increased to 127o with appropriate eye movements. The magnification of the laser spot in the retina is 1.5x, that is to say for a laser spot size of 200 μm, the size of burn in the retina will be 300 μm; for a spot size of 350 μm, the size of the burn will be 500 μm.

I usually complement the treatment with the Mainster PRP 165 lens or the Quadrasferic, which have the widest field of view, even though the resolution is not as good. Treatment with this lens up to periphery is especially important in treating proliferative diabetic retinopathy with high risk characteristics.

Anesthesia

PRP can usually be performed under topic anesthesia. However, some practitioners may prefer retrobulbar or peribulbar anesthesia. Retrobulbar or peribulbar anesthesia may be necessary in patients that do not tolerate the procedure.

Some degree of discomfort or pain is experienced by most patients. Most of the time the procedure can continue using simple measures, such as lowering the pace of the applications, increasing the size of the spots, avoiding the long ciliary nerves at 3 and 9 o’clock, and kindly reassuring the patients.

Laser Wavelengths

Argon green, Diode laser (810 mm) and double-frequency Nd: YAG (green=532 mm) or Krypton (red) and dye lasers seem to be equally effective in the treatment of proliferative retinopathy.

The diode laser, as well as the red laser, penetrates better lens opacities and blood in the vitreous and are less absorbed by blood in the retina. In cases of cataract or vitreous hemorrhage, diode or red laser may be more useful. However, it penetrates deeper in the choroid and its use may be more painful.

It appears there are not practical advantages of specific wavelengths in the treatment of diabetic retinopathy. The extent of photocoagulation is more important than the wavelength used.

Treatment Technique and

Parameters

It is important to realize that the size of the burn in the retina depends, not only of the size of the laser spot, but also of the

magnification of the lens and on the power and duration of the laser application, the transparency of the media and the pigmentation of the eye.

It is not possible therefore, to define the number and size of applications in performing PRP. Nor can we define the power of applications, since the power needed to obtain a burn in a pseudophakic is much lower that the required power for photocoagulation of the retina in a patient with lens or vitreous opacities. All that can be said is that the power is the minimum necessary to obtain a burn of medium intensity or gray-white (not “chalk white”).

The Early Treatment Diabetic Study Research Group(3) developed a protocol for scatter laser treatment that may serve as a general guideline for PRP (Table 2).

Size. If we are using a wide-angle lens, a spot size of 350 μm at the retina will be magnified to a burn of 500 μm at the retina, if we are using the proper power. If the power is too low, the burn will be smaller.

Exposure. We prefer an exposure of 0.2 seconds.

to equator and beyond, if possible. Burns should be placed 1⁄2 to 1 burn apart. We perform the basic procedure in two sessions, starting with the nasal retina if there is not impending risk of vitreous hemorrhage; if this is the case, we start for the inferior half of the retina. Patches of retinal neovascularization are treated with overlapping burns (Figure 7). After completing the two sessions, that may require 1200-1600 applications, the patient is observed and the need for additional treatment is determined at 45 to 60 days. Re-treatment is indicated if new vessels fail to regress or continue to grow despite initial treatment.

Number. The number of applications will change from patient to patient. Borders for treatment are one disc diameter nasal to the disc, just outside the temporal arcades and 4 disc diameters temporal to the fovea, up

Figure 7: Pan retinal photocoagulation, full. Only the nasal side was treated in the first session. Overlapping burns over a patch of retinal neovascularization (arrow).

Dosimetry of laser treatment varies according to the severity of retinopathy; in eyes with proliferative diabetic retinopathy with high risk characteristics, full PRP will be given up to the retinal periphery. Anterior segment neovascularization, rapid disease progression on associated signs of retinal ischemia, such as venous beading and IRMA and extensive capillary closing at the panoramic fluorescein angiography are also indication for heavy, full PRP.

In eyes with severe non proliferative diabetic retinopathy or initial proliferative diabetic retinopathy in which PRP was indicated, because of the accumulation of risk factors for progression or poor compliance, a “mild” scatter photocoagulation may be performed, with separation of burns (one or two burns apart), as initial treatment.

Complications

After PRP, the patient may experience decreased vision that usually resolves in a few days. However, some patients may loose 1 or 2 lines of visual acuity. A side effect associated with PRP includes a decrease in night vision, color vision and restriction of the visual fields. Driving at night or through a tunnel may become hazardous. Exudative retinal detachment or ciliochoroidal effusion is only observed when all treatment is delivered in one session, technique that we do no advice.

DIABETIC MACULAR

EDEMA

Evaluation of Diabetic

Macular Edema (DME)

Diagnosis and rational treatment of DME requires the following:

A.Stereoscopic examination of the macula at the slit lamp with a plane-concave lens such as the Goldmann lens.

may show wide spread leakage from the macular retinal capillaries (Diffuse leakage), due to a break down of the inner blood-retinal barrier. Cystoid macular edema will occur if the leakage is massive, with pooling of dye in the outer plexiform layer in the late phase of the angiogram.

Leakage of dye on F-A is not always associated with edema or thickening of the retina (if the rate of clearance of fluid out of the retina exceeds the rate of fluid ingress).

F-A may show small ischemic areas or a definite ischemic maculopathy, with an enlargement of the Foveal Avascular Zone (FAZ).

C.Optical Coherence Tomography (OCT).

OCT allows and objective assessment of macular thickness and rules out macular traction. It reveals the presence and extent of vitreomacular traction that may not be detectable with fundus biomicroscopy.

OCT also reveals the presence of subretinal fluid accumulation with or without vitreous traction.

B.Fluorescein angiography (F-A). Once the diagnosis of CME is made biomicroscopically, a fluorescein angiogram should be performed. F-A may show well defined areas of leakage from microaneurysm or dilated capillaries (Focal leakage) or

DME: Classification and Indications for Laser Treatment

The Global Diabetic Retinopathy Project Group(1) described a severity scale for DME,

defined as retinal thickening or hard exudates at the posterior pole:

•Mild DME: some retinal thickening or hard exudates in the posterior pole, but distant from the center of the macula.

•Moderate DME: retinal thickening or hard exudates approaching the center of the macula, but not involving the center.

•Severe DME: retinal thickening or hard exudates involving the center of the macula.

Laser treatment is not indicated in mild DME, but should be considered in moderate and severe DME, that is, if retinal thickening or hard exudates threaten or involve the center of the macula.

This classification is derived from the ETDRS classification (Table 3). The ETDRS proved that laser treatment reduced visual loss in patients with clinically significant macular edema and less severe retinopathy. Therefore, treatment should be considered for clinically significant macular edema; non clinically significant DME should be observed.

Medical Treatment

Once a diagnosis of clinically significant DME is made, our first concern should be to check the medical condition of the patient. DME is more likely to be present in individuals with hypertension, high glycosylated hemoglobin and proteinuria.(4) Retention of water by any cause may aggravate DME. High serum lipids are associated with vision loss due to macular edema and retinal hard exudates.(5)

The above mentioned risk factors for DME should be addressed and corrected, when possible, before considering laser treatment for DME.

Information to the Patient

•Laser photocoagulation reduces the risk of vision loss by 50%. Treatment is more effective at preserving than restoring vision.

•Re-treatment may be necessary.

•Patients may have paracentral scotomas.

•Very advanced and long standing cases do not benefit significantly.

Treatment of Diabetic Macular

Edema

Laser photocoagulation is the current standard of treatment for DME. The ETDRS study evaluated the effects of argon laser photocoagulation in a prospective, randomized multicenter clinical trial. Eyes assigned to immediate focal photocoagulation were half as likely to lose 15 or more letters on the ETDRS chart compared to eyes assigned to deferral of photocoagulation (12% vs. 24%) at three years. In eyes with an initial visual acuity of 20/40 or more, an improvement in visual acuity of 5 or more letters (more than one line on the ETDRS chart) was much more frequent in eyes assigned to treatment. Improvement of visual acuity by 15 letters was uncommon (<3%).(6)

The ETDRS recommended direct treatment to cover areas of diffuse DME and capillary non perfusion. For focal treatment of retinal microaneurysms a small spot of 100 μm should be used. (We think that a smaller not of 50 μm is potentially dangerous).

Focal versus Diffuse Diabetic Macular Edema

There is not a clear, universally accepted definition of focal DME and diffuse macular edema. Many cases have mixed features,

making a distinction difficult.(7) These terms should be used with caution.

Focal DME. These patients usually show lipid exudates associated with retinal thickening, often in the form of circinate rings. On fluorescein angiography these eyes have a

high proportion of leakage originating from microaneurysms(Figure8). TheETDRSgraded the source of leakage for classification of DME as focal or diffuse. Eyes with 67% or more of leakage associated with microaneurysms were classified as focal.(8)

OCT will show retinal thickening in the area of the leaking microaneurysms or capillary. The OCT map, will show the thickened area, where laser treatment should be

concentrated (Figure 9). Isolated areas of hot colors are surrounded by larger areas of cool colors.

Besides optimizing medical treatment, laser is the only accepted treatment for this type of DME. (Figure 10). If DME persists after the initial treatment, leaking lesions closer to the fovea may be treated up to 300 μm from the center of the fovea.

DiffuseDME. Themacularareaisdiffusely thickened at the biomicroscopic examination. Lipid exudates are less prominent and usually do not show a circinate ring pattern.

Fluorescein angiography shows diffuse leakage of dye from the perifoveal capillaries

with a generalized breakdown of the bloodretina barrier (Figure 11). Eyes with 33% or less of fluorescein leakage associated with microaneurysm were classified as diffuse DME by the ETDRS.(8) Fluorescein angiography may show cystoid spaces (Figure 12). OCT usually show increased macular thickness involving all quadrants, with loss of the foveal depression (Figure 13). A cystic pattern and/or a localized serous detachment of the macula may be demonstrated in some cases (Figure 11).