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

There are many facts that can accelerate the syneretic process in the eye: myopia, trauma, intraocular inflammation, eye surgery or hereditary syndromes.

Posterior Vitreous Detachment (PVD)

Posterior vitreous detachment is strongly related to syneresis. Only a small amount of liquefaction is tolerated by the vitreous before it separates from its posterior attachment.3 Once the vitreous is liquefied, at some point a break develops in the posterior cortical vitreous, through which the liquefied vitreous passes abruptly into the subhyaloid space, this separates the posterior hyaloid from the retina and progresses anteriorly towards the vitreous base where it remains attached.

This event usually takes place in patients age 50 or older, even when many patients do not report acute symptoms, most will describe photopsias from physical stimulus of vitreoretinal traction and floaters caused by vitreous opacities such as blood or aggregated collagen fibers. Patients with these symptoms should be seen promptly, specifically looking for retinal breaks that could have taken place during posterior vitreous detachment. Some patients may suffer rupture of retinal vessels and vitreous hemorrhage, or a slight retinal hemorrhagic trace.

From all the facts associated with retinal detachment this is probably the most important.

Vitreoretinal Attachments

Normal vitreous is firmly attached to some areas of the retina. The strongest attachment takes place at the vitreous base2,4 which is a circumferential zone located 5 mm behind the limbus straddling the ora serrata, measures approximately6mm,andextends2mmanterior and 4 mm posterior to the ora.

The second strongest attachment is located at the margin of the optic disc. When PVD occurs the ring of attachment (Weiss ring) can be identified by ophthalmoscopy floating in the vitreous above the optic nerve head and may be accompanied by vascular ruptures and vitreous hemorrhage.

Finally there are other normal attachments, not as strong as the ones mentioned before, at the veins located in the mid-periphery of the retina.

Abnormal attachments of the vitreous can be found in chorioretinal scars or peripheral degenerations such as lattice, because of its clinical significance this will be discussed separately.

Peripheral Retinal Lesions

There is a great variety of anatomic variations and degenerations in the retinal periphery, some of them lack clinical significance since they do not play a causative role in the development of RD (Table 2). Thus it is important to understand, recognize

Next we will group the lesions according to their clinical behavior in order of importance:

Lesions Predisposing to Retinal Detachment

1.Lattice degeneration

2.Cystic retinal tuft

3.Degenerative (Senile) retinoschisis.

4.Trophic retinal holes

5.Retinal tears

6.Dialysis

1.Lattice Degeneration

This is the most important among peripheral retinal lesions, it has been associated

with a 20-30%5 incidence of rhegmatogenous retinal detachments. This was first described in 1930 by Jules Gonin6, and it was until 1952 that Schepens7 designated this entity. Hystologically (Figure 1) consists of localized retinalthinningoverlyingvitreousliquefaction, with strong vitreoretinal attachments at the margins of the lesion8.

The pathogenesis of lattice is still unknown.

Often they are located anterior to the equator, in the vertical meridians and the inferior quadrants, and found bilateral between in 30-50% of patients. Its incidence is higher in myopic patients, occurring in 15% of eyes with axial length of 30mm or more9. This degeneration can be found in 10-35% of eyes with a collateral retinal detachment.10

Figure 1: Lattice Degeneration (Courtesy: Dr. Oliver

Schneider).

There are very interesting variations in the appearance of lattice degeneration: white lines, snail tracks, various degrees of pigmentation, presence of holes or tears.

The main danger in lattice takes place during posterior vitreous detachment formation, since retinal tears can form from vitreous traction; these tears have been found associated to lattice in 1.5%.11 Because of its association with retinal detachment this is a good combination of facts to consider prophylactic laser treatment.

Holes have been described in lattice degeneration in 16-24%,9 and in the presence of posterior vitreous detachment they have been associated to retinal detachment. Approximately 2.8% of rhegmatogenous retinal detachments are due to retinal holes within a lattice,12 this represents a low risk in order to justify prophylactic treatment.

2. Cystic Retinal Tuft

These are elevated vitreoretinal lesions, small, round or oval, sharply circumscribed and have chalky-white color.

Histologically consist of dense accumulations of glial tissue in small nodules on the surface of the retina, enclosing crypts of formed vitreous intimately attached to the overlying vitreous,13 often have been associated with pigmentation and trophic changes in the adjacent retina.

They are commonly associated with retinal tears, and it has been estimated that up to 10% of retinal detachments are caused by retinal tears in areas of cystic retinal tufts.14 It has also been established in autopsy reports that they can be found in 5% of the population.

The risk of developing retinal detachment from a cystic retinal tuft is 0.28% so their prophylactic treatment is not indicated.15

3. Degenerative (Senile) Retinoschisis

Was first described in 1933 by Bartels16 as an idiopathic degenerative process which clinically presents as a peripheral, smoothly elevated lesion with a convex posterior border. It is frequently asymptomatic bilateral an located in the inferior temporal quadrants.

During ophthalmoscope, examination and scleral indentation can be differentiated from a retinal detachment because it has a “white with pressure” sign.

By histopathology this lesion begins in the outer plexiform or inner nuclear layer of the peripheral retina as a degeneration of neuroretinal and glial supporting elements. Gradual accumulation of mucopolysaccharide causes it to enlarge (Figures 2, 3).

When breaks are found in the external layers a retinal detachment can develop. Retinoschisis is present in up to 6% of retinal detachments, but is responsible only for less than 2.5%.17

The natural course of this type of lesions does not show progression therefore treatment must be limited to progressive symptomatic cases with associated retinal detachment.

Laser demarcation treatment or treatment of the holes within a retinoschisis should be avoided since it has been associated with severe complications such as creation of larger breaks increasing its association with retinal detachment.

4. Trophic Retinal Holes

These are degenerative lesions not associated to vitreous traction. By histopathology there is a progressive loss of neurosensorial retinal layers creating a full thickness defect, often surrounded by pigment clusters. Retinal holes can appear anywhere in the retina, but are found more often between the equator and retinal periphery.

They have been described as occurring more frequently in highly myopic patients but have also been found in emetropic eyes.

Figure 2: Retinosquisis 10X (Courtesy: Dr. Oliver Schneider).

Figure 3:(Courtesy: Dr. Oliver Schneider).

These lesions have different configurations: arrow head, horseshoe, L shape, H shape etc.

When the tear takes place over a vessel, vitreous hemorrhage can appear and has been reported that 70% of patients with vitreous hemorrhage associated to posterior vitreous detachment have tears. However, it may manifest just with photopsias and myodesopsias.18

The treatment of a recent, symptomatic retinal tear is not a matter of controversy, since these lesions are highly related to retinal detachment, prompt laser treatment is indicated.

6.Dialysis

This lesion is defined as a separation of the retina from its insertion at the ora serrata, they can be of either idiopathic or traumatic origin.

The first type occurs spontaneously, not associated to vitreous traction, located in the inferotemporal quadrant. Young males are more affected. Whenever a dialysis is found whether associated or not to retinal detachment it is mandatory to specifically search the other eye, since it is often bilateral.

Dialysis can cause a slowly progressive inferior retinal detachment, so laser treatment is indicated.

Dialysis of traumatic origin are preceded by direct contusion of the globe, the superonasal

quadrant is affected more often and can be associated to vitreous base avulsion. Since these are also related to retinal detachment, laser treatment is indicated.

INDICATIONS FOR LASER

TREATMENT

The accurate selection of cases that can benefit from prophylactic laser treatment is still a matter of controversy; the decision must be based in all the factors we discussed previously.

There are retinal lesions that nobody would doubt in treating, such as a symptomatic superior retinal tear, meanwhile a small trophic pigmented asymptomatic retinal hole located inferiorly probably would not benefit form treatment. Between these two examples a great variety of lesions exist, and good clinical judgment and experience is required in order to avoid unnecessary treatment.

We must keep in mind that retinal detachment is infrequent, affecting 1 in 10,000 - 20,000 patients a year, while peripheral retinal degenerations can be found in 6 to 14% of the general population.4,20

There are a lot of variables that must be taken into consideration before indicating treatment: Presence of symptoms, location of the lesion, type, size, presence of subretinal fluid, age, family history of retinal detachment, collateral eye condition, refractive error, life expectancy, occupation, associated conditions such as aphakia or pseudophakia.20

The presence of symptoms such as entoptic phenomena is indicative of vitreoretinal traction, floaters are related to posterior vitreous detachment and also can be referred by patients with associated vitreous hemorrhage.

Superiorly located tears above the horizontal meridians are considered more dangerous, since they can produce rapidly progressive retinal detachments.

Tears found posteriorly are also dangerous since those are more in contact with intraocular currents if the vitreous is liquefied.

Laser Photocoagulation

Among all different treatment methods to produce retinopexy (chorioretinal adherence) argon laser is the most popular.22 In the history of retinal detachment many methods have been used: diathermy, criotherapy, xenon photocoagulation. But adverse effects such as epiretinal membranes and higher incidence of proliferative vitreoretinopathy have made argon laser a better technique19 (Table 3).

The presence of subretinal fluid surrounding a lesion makes us think of the need of prompt laser treatment.

Aphakia or pseudophakia combined with posterior capsule rupture increase the risk of retinal detachment.

As mentioned previously, lattice degeneration has firmly attached vitreous to its margins, so when acute posterior vitreous detachment takes place, tears can develop.

We must keep in mind that the objective of laser treatment is to create a barrier that blocks the transit of liquefied vitreous through a retinal break.

The chorioretinal scar generated by laser is not strong enough to avoid a retinal break formation during acute posterior vitreous detachment, thus it would not be useful to treat lattice degeneration if the vitreous is still attached, here the best behavior would be close observation.23

Table 3

Argon green laser energy is completely absorbed by the retinal pigmentary epithelium and has little if no penetration to choroidal layers. It creates a gray-white burn by protein denaturalization involving internal and external retinal layers. Another advantage of this method is the great variety of application techniques; from the traditional method with a three mirror lens and slit lamp which allows easy visualization of the retinal periphery, the indirect ophthalmoscope with scleral indentation, to the laser probe used during vitrectomy surgery.

Different lasers have been used in prophylactic treatment of peripheral retinal lesions such as the Argon (514 nm), diode (810nm) and krypton (647nm) lasers (Table 4).

Table 4

Diode laser acts in the infrared, invisible specter and its absorption characteristics vary from argon laser. It penetrates deeper into the choroid, similar to the krypton, requires more energy in order to create a similar scar, and is more painful. Nevertheless it has been reported as efficient as argon laser. It has also been speculated that when creating deeper burns the chorioretinal adherence generated is more effective than with argon, but also increases the risk of Bruch́s membrane rupture and choroidal hemorrhage.24

Therefore argon laser is the preferred method when applying laser treatment.

Techniques for Laser

Application

Once we have decided to treat a lesion and explained the patient the technique, the pupil should be widely dilated, with the patient sitting in front of the slit lamp and with a three mirror lens, the lesion must be located. In order to begin with light gray burns power is adjusted in approximately 200mw and with exposure time of 0.5 seconds. Size can vary between 200-500 microns. These parameters can be increased gradually until gray-white burns are obtained.

Densely pigmented eyes require less intensity in order to achieve an effective chorioretinal scar compared to less pigmented eyes. Nuclear sclerosis of the lens, vitreous hemorrhage or pigment can interfere with laser treatment.

Lesions must be surrounded with contiguous burns starting from the margins and placing 3 or 4 lines, avoiding treatment of choroidal tissue (Figure 6A-B).

If the decision of prophylactic treatment of a lattice degeneration has been taken, not only the break within is treated, the margins of the lesion (lattice) should be completely surrounded.

When the lesion is located in the periphery and the anterior border is hard to reach, scleral indentation can be helpful, sometimes it might be necessary to consider a different method such as cryotherapy. This method could also be considered in cases of opaque media (Table 5).

Complications

Laser treatment as a retinopexy method has only a few complications compared to cryotherapy, xenon photocoagulation or diathermy.

Epiretinal membrane formation has been reported with excessive treatment. When using small diameter laser burns (100-200 microns) accidental rupture of retinal vessels can happen.

B

Figure 6: A) Retinal tear already treated with laser. B) Final View of Buckle with Retinal Indentation and Laser Sealing. This internal/external conceptual illustration shows a cross section and corresponding surgeon´s view of the final configuration of a circumferentially placed sponge exoplant (E). The cross section shows a portion of sclera (S) removed for clarity. The surgeon´s view is through the indirect ophthalmoscope (O). Note the indented configuration in both views. The retina is reattached and the tear (T) is flat. Also note that the tear is properly positioned on the anterior slope of the invagination. (B: Art from Jaypee-Highlights Medical Publishers).

The Role of Laser Treatment in Peripheral Lesions Predisposing to Retinal Detachment

We must keep in mind that the role of laser treatment in this type of lesions is to create a scar surrounding its margins, not mainly to increase chorioretinal adhesion, but to block the flow of liquefied vitreous to the subretinal space; thus the protective role of treating lattice or tufts does not really exist, because when a break from acute posterior vitreous detachment is generated even if previously treated it can pull and elevate the retina despite laser burns.

Careful evaluation of each patient is needed, and every fact must be taken into consideration before indicating prophylactic

laser treatment. Laser is a useful tool and should be used prudently. Photocoagulation is clearly indicated in retinal tears with persistent vitreous traction upon flaps of the tears. For most other entities, evidence of important value is still lacking. The best evidence-based recommendations for prophylactic therapy are contained in an American Academy of Ophthalmology publication.26

References

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24.Isola,V Spinelli,G Misefari,W .Transpupillary retinopexy of chorioretinal lesions predisposing to retinal detachment with the use of diode (810 nm) microlaser. Retina 2001, Vol 21 Number 5:456-4.

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26.American Academy of Ophthalmology Preferred Practice Pattern: Management of posterior vitreous detachment, retinal breaks, and lattice degeneration. San Francisco, CA:1998.