What are the mechanisms of injury to the fundus in blunt trauma?

Blunt trauma to the sclera can produce a direct effect on the underlying choroid and retina. In addition, a concussive effect from force transmitted through the vitreous may be seen away from the initial point of impact. The sudden deformation of the globe may cause stretching of the retina and retinal pigment epithelium (RPE) and traction on the vitreous base. The shearing forces generated by this traction may tear the retina in the area of the vitreous base or result in avulsion of the vitreous base. Forces can be severe enough to avulse the optic nerve ( Fig. 42-1 ).

Optic nerve avulsion after severe blunt trauma.

What clinical entity is caused by the contrecoup mechanism?

Indirect damage from the concussive effect of an injury tends to occur at the interfaces of tissue with the greatest differences in density, most commonly the lens–vitreous interface and the posterior vitreoretinal interface. The transmitted force may cause fragmentation of photoreceptor outer segments and damage to the receptor cell bodies. Clinically, these areas appear as opacified retina and are termed commotio retinae . Although the retinal whitening is only temporary, resolving over 3 to 4 weeks, permanent damage may occur. Loss of vision depends on the amount and location of early photoreceptor loss. The RPE underlying an area of commotio may develop a granular hyperpigmentation or atrophic appearance and lead to decreased vision. The eponym associated with this entity is Berlin’s edema; however, there is no true intracellular or extracellular edema, and no fluorescein leakage is seen.

Name the five types of retinal breaks seen in fundus trauma.

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  Retinal dialyses

  
  
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  Horseshoe tears

  
  
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  Operculated holes

  
  
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  Macular holes

  
  
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  Retinal dissolution (necrosis)

Where are retinal dialyses most commonly seen?

Retinal dialyses are usually located in the superonasal or inferotemporal quadrants ( Fig. 42-2 ). Trauma is more clearly related to superonasal than to inferotemporal dialyses. Dialyses may be associated with avulsion of the vitreous base. Because they can lead to retinal detachment, a careful depressed exam of all patients with a history of blunt trauma is essential. Prophylactic treatment of all dialyses with cryopexy or laser photocoagulation is recommended in the hope of decreasing the likelihood of future retinal detachments.

Retinal dialysis (arrow) with associated chronic retinal detachment through contact lens.

When do retinal detachments occur with dialyses?

Retinal detachments present at variable intervals after injury; however, the dialysis is usually detectable early or immediately at the time of injury. Approximately 10% of dialysis-related detachments present immediately, 30% within 1 month, 50% within 8 months, and 80% within 2 years. Most trauma victims are young, with a formed vitreous that tamponades a break or dialysis, but as the vitreous eventually liquefies, fluid passes through retinal breaks causing detachments. The nature of the vitreous in such cases may explain the delay in presentation of the detachments.

In addition to retinal dialyses, do other trauma-related breaks need to be treated prophylactically?

Horseshoe tears and operculated holes in the setting of acute trauma are usually treated by cryopexy or laser photocoagulation. Macular holes require pars plana vitrectomy with gas exchange if closure of the hole is attempted; however, macular holes usually do not progress to retinal detachments. Surgery is not performed for the purposes of prophylactic closure. Direct injury with necrosis of the retina is usually associated with underlying choroidal injury so that a chorioretinal adhesion may be formed spontaneously. However, any accumulation of subretinal fluid or persistent traction on damaged retina makes prophylactic treatment reasonable.

What is the prognosis for repair of a retinal detachment associated with a dialysis?

Dialysis-related detachments are usually smooth, thin, and transparent. Intraretinal cysts are common, and half have demarcation lines. In addition, proliferative vitreoretinopathy is rare. The characteristics of the detachment are suggestive of its chronic nature and insidious onset; however, the prognosis for repair with conventional scleral buckling techniques is good.

Are traumatic macular holes the same as typical macular holes?

Traumatic macular holes often behave differently compared to a typical macular hole formed as a result of vitreoretinal interface disease. Traumatic macular holes that form immediately at the time of initial injury may close spontaneously. Those that fail to close after a few months of observation can be anatomically improved by surgical intervention. However, the improvement in vision may be disappointing. The initial trauma can result in retinal damage that is incompatible with good vision. Careful consideration by the surgeon in discussions with the patient is required before considering surgical intervention.

Describe the clinical features of a choroidal rupture.

The retina is relatively elastic, and the sclera is mechanically strong. The Bruch’s membrane, the structure between the retinal pigment epithelium and the choriocapillaris, is neither elastic nor strong. Consequently, it is susceptible to the stretching forces exerted on the globe in blunt trauma. The Bruch’s membrane usually tears along with the choriocapillaris and RPE. Choroidal ruptures may be found at the point of contact with the globe or in the posterior pole as a result of indirect forces. Clinically, choroidal rupture appears as a single area or multiple areas of subretinal hemorrhage, usually concentric and temporal to the optic nerve ( Fig. 42-3 ). The hemorrhage may dissect into the vitreous. As the blood resolves, a crescent-shaped or linear white area is seen where the rupture occurred. With time, surrounding RPE hyperplasia or atrophy may be seen. Linear white areas are most consistent with a fibrotic response following the resolution of the hemorrhage. This can be seen on optical coherence tomography (OCT) ( Figs. 42-4 and 42-5 ).

Choroidal ruptures (large arrowheads) located concentric to the optic nerve. The small arrowhead indicates the center of the associated subretinal hemorrhage.

Choroidal rupture color photograph corresponding to OCT scan in Fig. 42-5 .

An OCT scan through the choroidal rupture in color photograph Fig. 42-4 . There is an elevated mound of fibrosis visible at the level of the choroid (yellow arrow) with an absence of normal retinal architecture. Areas of disrupted outer retinal anatomy with absence of the ellipsoid line are shown by the white arrows. The orange arrowheads indicate increased transmission through the damaged RPE.

Are there any long-term complications of choroidal ruptures?

The visual consequences of a choroidal rupture depend on its location with respect to the fovea. A patient with a choroidal rupture near the fovea may have good vision; however, the break in the Bruch’s membrane predisposes him or her to the development of a choroidal neovascular membrane, which may threaten vision long after the initial injury. Therefore, patients at risk should be followed regularly and advised of the potential complication.

Can orbital adnexal trauma result in fundus abnormalities?

High-velocity missile injuries may cause an indirect concussive injury to the globe, resulting in retinal breaks and ruptures in the Bruch’s membrane that resemble a claw. A fibroglial scar with pigment proliferation forms, but retinal detachment is rare, possibly because a firm adhesion develops, acting as a retinopexy. Chorioretinitis sclopetaria is the name given to this clinical entity.