Retinal artery occlusion

Retinal artery occlusion is a true ocular catastrophe. If the central retinal artery is obstructed (i.e., central retinal arterial occlusion [CRAO]) by an embolus or thrombus, resulting in retinal nonperfusion, the nine layers of the retina undergo ischemic necrosis, resulting in a sudden and painless loss of vision to the affected eye.

Some studies suggest no detectable retinal damage if retinal blood flow is restored within 60 to 90 minutes; subsequent partial recovery may be possible if ischemia is reversed within 240 minutes.

The diagnosis is based on the retinal finding of the classic cherry-red spot. The retina becomes gray from swelling or edema because the retina loses its normal transparency. The blood vessels become attenuated and segmented ( Fig. 24.1 ). Ischemic changes make the entire nerve fiber layer of the retina gray except in the foveal region which is devoid of the nerve fiber layer. Consequently, the background in the fovea remains a normal red color from the underlying choroidal vascular supply, leading to the appearance of a cherry-red spot. The usual prognosis is total and permanent loss of light perception in the involved eye ( Fig. 24.2 ).

Central retinal artery closure, acute. Note the graying in the macular area and the cherry-red spot.

Hole in the macula. Note the “punched-out” reddened area.

If a branch of a retinal artery is involved, the prognosis is often better. Patient may have a permanent visual field deficit, or may not notice any changes in their vision.

In elderly patients, a retinal arterial occlusion (RAO) may be secondary to a life-threatening medical emergency, namely, giant cell arteritis (GCA). In patients over the age of 60 years with an RAO, GCA should be suspected and appropriate laboratory and medical workup should be done immediately. As well, patients presenting with an RAO should be urgently referred to a stroke center for appropriate systemic medical workup to diagnose and optimize their stroke risk factors.

Similar to retinal vein occlusions (see later), RAOs can lead to subsequent macular edema (swelling within the macula), development of abnormal neovascularization within the anterior and posterior segments, and lead to sequalae of glaucoma, vitreous hemorrhage, and retinal detachment. As such, patients with RAO should be examined every 3 to 6 months by the ophthalmologist or the retinal specialist to monitor for these findings.

Retinal vein occlusion

Central retinal vein occlusion (CRVO) is generally caused by a thrombus in a central retinal vein. Conditions associated with an increased risk of retinal vein occlusion include diabetes, hypertension, polycythemia, glaucoma, and any other condition that causes stasis of blood flow.

Because there is no pain, the patient may not be immediately aware of the onset of the condition. The profound loss of vision may not be detected until the patient “discovers” it by rubbing or closing the good eye.

On ophthalmoscopic examination, the entire retina may be covered with superficial hemorrhages that appear flame shaped ( Fig. 24.3 ). There may be scattered cotton-wool spots, which are microinfarcts of the retinal nerve fiber layer. The retinal veins appear dilated and tortuous distal to the site of occlusion. The macula is usually edematous and this leads to cystoid macular edema with loss of vision. If a branch of the vein is involved, only one sector of the retina will be affected so the vision may or may not be affected. The prognosis for visual recovery is significantly better with a branch vein occlusion than with a central vein occlusion.

Central venous occlusion. Note multiple hemorrhages and distended vessels.

(Courtesy Mount Sinai Hospital, Toronto.)

The chances for significant visual recovery in an ischemic CRVO are generally poor. The most dreaded complication is neovascular glaucoma, which can result in a blind eye with severe pain that may eventually be managed by enucleation. With ischemia, there is proliferation of new blood vessels that can occur on the iris and extend over the trabecular meshwork, resulting in obstruction of aqueous outflow and elevated intraocular pressure, hence the term neovascular glaucoma.

Once the diagnosis of a CRVO is made, a fluorescein angiogram is usually performed to determine the degree of retinal ischemia. If there is significant ischemia, laser photocoagulation to all peripheral ischemic retina (i.e., panretinal) can be performed. This is thought to destroy areas of ischemic retina that are probably responsible for producing a chemical mediator that leads to neovascularization, the formation of new blood vessels. Although the initial studies looking at laser photocoagulation in the treatment for CRVO demonstrated no beneficial effect, more recent studies (CRUISE, COPERNICUS, and GALILEO) have demonstrated that the use of intravitreal antivascular endothelial growth factor (anti-VEGF) inhibitors results in rapid and sustained improvement in visual acuity and central foveal thickness for patients with macular edema secondary to CRVO.

Similarly, if there is macular involvement in branch retinal vein occlusion (BRVO; see Fig. 24.3 ), then vision will be affected. Studies involving BRVO have demonstrated that if vision has been decreased for more than 3 months and fluorescein angiogram shows a leakage of fluid in the macula, laser photocoagulation in a sector distribution can improve the visual prognosis. The risk of neovascular glaucoma is generally less of a concern with BVO.

More recent studies (BRAVO, CRUISE, HORIZON, and VIBRANT) have shown that monthly injections of anti-VEGF (bevacizumab, ranibizumab, or aflibercept) improved both visual acuity and central foveal thickness in patients with macular edema secondary to branch vein occlusion.

Patients with venous occlusive disease should have a general medical evaluation to rule out diabetes, hypertension, or blood dyscrasias. The ophthalmologist must evaluate the nonaffected eye to rule out glaucoma, which is commonly associated with vein occlusions.

Diabetic retinopathy

Diabetic retinopathy is currently a prominent cause of vision loss around the world. Diabetic retinopathy affects over 350 million individuals worldwide, particularly between the ages of 20 and 70 years old with an estimated 10,000 new cases of blindness per year in the United States. These numbers are projected to continuously increase with the increase prevalence of diabetes mellitus. Fortunately, numerous clinical trials (DCCT and UKPDS) have demonstrated a significant reduction in ocular complications with aggressive control of blood glucose, blood pressure, and hemoglobin A1C levels.

Diabetes may have a juvenile or adult onset. In general, the incidence of diabetic complications increases with the duration of the disease. Complications may include systemic and ocular problems. Systemic complications include microvascular and macrovascular complications. Microvascular complications of diabetes include peripheral neuropathy and nephropathy, as well as diabetic retino-pathy. Macrovascular complications include a heightened risk of stroke, myocardial infarcts, and other cardiovascular disease. Diabetic retinopathy is divided into nonproliferative and proliferative stages.

Nonproliferative diabetic retinopathy (NPDR) is further classified into mild, moderate, and severe retinopathy. NPDR is characterized by the presence of microaneurysms (small vascular buds), dot and blot hemorrhages, and lipid exudates from a serous leakage of the retinal vessels ( Fig. 24.4 ). Other findings include the presence of cotton-wool spots (microinfarcts of the retina), irregular dilatation of retinal veins, and intraretinal microvascular abnormalities, which are abnormal capillaries within the retina as a result of ischemia.

Diabetic retinopathy. The retinal changes occur predominantly at the posterior pole with microaneurysms and “dot and blot” hemorrhages and hard exudates occur in the macular area.

Proliferative diabetic retinopathy is defined by the presence of abnormal blood vessel formation—that is, neovascularization on the optic disc, the surface of the retina, or the iris. These fragile aberrant blood vessels are easily ruptured, causing recurrent vitreous hemorrhage. These abnormal blood vessels can also contract to form fibrovascular scar tissue that can provide traction on the retina, resulting in tractional retinal detachment. Aberrant neovascularization within the anterior segment, including the iris with extension to the trabecular meshwork, can lead to neovascular glaucoma.

Ocular treatment modalities for diabetic retinopathy depend on the stage of the disease and the absence or the presence of a variety of complications. If neovascularization is present, then panretinal photocoagulation (PRP) is the treatment of choice. Approximately 2000 to 3000 photocoagulation spots are applied to the peripheral retina with the argon laser, essentially destroying the ischemic retina, which is thought to be the source of vasoproliferative factors. As well, laser photocoagulation to the peripheral retina reduces overall retinal oxygen demands and increases oxygen delivery to other portions of the retina, the macula, and the optic nerve. This treatment reduces and often resolves the neovascularization.

PRP can be done in the office, or intraoperatively if the patient requires vitrectomy surgery. In recent years, studies have indicated that anti-VEGF medications may be a good adjunct or alternative to PRP in patients with proliferative diabetic retinopathy who are reliable to follow up (see later).

If vision is decreased by macular edema outside the fovea, photocoagulation of leaking microaneurysms in the macular area has been shown to improve vision. If the patient has a nonclearing vitreous hemorrhage, or if there are fibrovascular bands producing a tractional retinal detachment, a pars plana vitrectomy is the surgical procedure of choice. The vitrectomy infusion suction and cutting instruments are introduced over the pars plana and the vitreous hemorrhage is removed and replaced with saline. The tractional bands are also cut and released allowing the retina to reattach to its normal position.

Multiple studies have implicated VEGF as the main culprit in the pathogenesis of diabetic retinopathy and diabetic macular edema. The retina becomes ischemic because of capillary damage from diabetes. Ischemic areas of the retina produce VEGF and other chemical factors resulting in neovascularization, the proliferation of abnormally formed blood vessels. These abnormal blood vessels are fragile and may leak (causing macular edema), bleed (causing vitreous hemorrhage), and eventually form fibrovascular scar and traction, ultimately causing tractional retinal detachment and blindness. After decades of clinical trials, the use of recombinant antibodies specifically targeting VEGF has been shown to not only restore the integrity of blood-retinal barrier, minimizing serum leakage, but also to dramatically improve vision in the majority of patients with diabetic macular edema. The three most commonly used anti-VEGF medications are: bevacizumab (Avastin), ranibizumab (Lucentis), and aflibercept (Eyelea). Multiple pivotal studies (RESTORE, READ2, RISE/RIDE, DA VINCI, VIVID, and VISTA) and results released by Diabetic Retinopathy Clinical Research Network (DRCR.net) demonstrated that intravitreal anti-VEGF blocks the effects of VEGF and significantly improves vision loss from diabetic macular edema.

The management of diabetes requires a coordinated effort between healthcare providers, including the ophthalmologist, general practitioner, endocrinologist, and dietician. Although technologic advances have been beneficial, diabetic retinopathy remains one of the leading causes of blindness in North America.

Educating diabetic patients regarding the sequelae of diabetic retinopathy and macular edema, and the importance of blood glucose and blood pressure control is of utmost importance for all eye care professionals.

Retinitis pigmentosa

Retinitis pigmentosa (RP) is a complex genetic disorder with a variable pattern of transmission. RP may be inherited as a sex-linked trait or as an autosomal dominant or recessive trait. RP can be classified into various subtypes, but symptoms common to many cases of RP include nyctalopia (difficulty seeing in dim illumination) and progressive loss of peripheral visual field. The subtype classification of a case of RP depends on the nature of the condition and its duration. RP may be mild or may progress to cause severe blindness. Disease severity is often worse in those who begin presenting symptoms in childhood or adolescence, as compared with those who initially present in adulthood.

It is not inevitable that each case will develop and cause constricting field loss. Some cases of RP remain stable for a lifetime.

The diagnosis can often be made with direct visualization of the fundus using ophthalmoscopy. The following findings are characteristic features:

• 1.
  

  Bone spicule-like pigment debris in the midperiphery of the retina ( Fig. 24.5 )

  
  

  
  

  
  

  

  
  

  
  

  Retinitis pigmentosa. Note attenuated arterioles, bone spicule pigment formation in the periphery, and waxy pallor of the optic disc.

  
  
  
  
• 2.
  

  Retinal vessel attenuation

  
  
• 3.
  

  Tubular visual fields

  
  
• 4.
  

  A waxy pallor of the disc

  
  
• 5.
  

  Posterior subcapsular cataract

Occasionally, a patient will present with typical symptoms but no retinal pigment dispersion. An electroretinogram (ERG) will show depressed rod function, despite the absence of characteristic retinal changes.

Although those with RP may experience night blindness, this symptom may also be caused by vitamin A deficiency, syphilis, and glaucoma. RP may also be accompanied by other comorbid conditions, such as deafness, metabolic abnormalities, and mental retardation.

At this time, there is no specific treatment or cure for this disease. Treatment with 15, 000 IU/day of vitamin A palmitate has been suggested. It is important to elicit a genetic tree from the patient so that genetic counselling can be undertaken. Follow-up is imperative in monitoring patient progress; both in ensuring that any arising conditions or complications are treated, and to help the patient maintain morale. In keeping with maintenance of morale, patients should be directed to their local RP support group or charity for therapy, financial assistance, and community support.

Retinopathy of prematurity

Retinopathy of prematurity (ROP) is a proliferative vascular disease occurring in premature infants exposed to high concentrations of oxygen soon after birth. The fibrovascular proliferation can have devastating sequelae leading to vision loss in severe cases.

Babies who are born prematurely, specifically those of gestational age less than 31 weeks or birth weight under 1500 g or premature babies with an unstable clinical course from birth, should be screened for ROP by an ophthalmologist until full vascularization of retina is completed. ROP is classified into stages from presence of a demarcation line between ischemic and vascularized retina to presence of neovascularization to partial or total retinal detachment.

Prevention of this disease is of the utmost importance. The pediatrician should try to use the lowest oxygen level that is compatible with good neonatal care. An eye examination should be done on all premature infants, especially those with a complicated course and who received significant oxygen therapy. Careful follow-up examinations should be performed to rule out any fibrovascular proliferation. Treatment of ROP may include observation for spontaneous regression, laser photocoagulation (ET-ROP study), intravitreal anti-VEGF therapy (BEAT-ROP study), vitrectomy, or retinal detachment surgery.

Retinoschisis

Retinoschisis is the abnormal splitting of the retina’s neurosensory layers. Partial-thickness inner or outer retinal hole formation are commonly associated with retinoschisis. There are two main classes of retinoschisis: degenerative and hereditary X-linked juvenile retinoschisis (XLJR). The partial-thickness split occurs in the outer plexiform layer in degenerative retinoschisis, and the nerve fiber layer in XLJR. A degenerative retinoschisis usually occurs in the peripheral retina and therefore rarely affects central vision. This condition occurs in 3% of the general population and almost never leads to a retinal detachment. Hereditary XLJR, on the other hand, is an X-linked recessive disorder, primarily affecting young males. Unlike the degenerative form, hereditary juvenile retinoschisis commonly affects central vision as a result of central foveal schisis, in addition to the peripheral retinal schisis.

Retinal breaks

Retinal breaks may take the form of holes or tears. A retinal tear is produced if the operculum, or the everting lip of retinal tissue, is still attached to the retina. A retinal hole is produced if the operculum is free from the retina ( Fig. 24.6 ). A retinal hole is often the result of an atrophic process that leads to a full thickness defect of the retina. If it occurs in the macula, retinal holes can cause permanent loss of vision to 20/200 or less. Vitreous detachment, a degenerative process, can result in a separate form of retinal hole or tear, as vitreous traction pulls off a small piece of retina in the retinal periphery. Most retinal tears and holes occur in the periphery of the retina and detection requires a fully dilated pupil and visualization with an indirect ophthalmoscope (see Fig. 24.3 ). Retinal tears should be treated by applying laser photocoagulation around the tear or hole. This method allows for scar tissue formation, thereby preventing retinal detachment by the entry of liquefied vitreous through the tear. The use of laser in this setting can be thought of as analogous to spot-welding, preventing liquefied vitreous from separating the retina from the underlying retinal pigment epithelium (RPE). Treatment by laser photocoagulation is suitable for patients experiencing flashing lights or floaters in their vision with clinical findings of retinal holes or tears.

Retinal detachment and horseshoe tear of retina.

Retinal detachment

Three things are required for a retinal detachment to occur: the presence of a retinal hole or tear, the invasion of liquefied vitreous under the sensory layers of the retina (causing the retina to “peel off”), and traction. Retinal detachments are usually rhegmatogenous (retinal tear induced). Vitreous traction is the major cause of retinal tears and this almost always occurs spontaneously. Although trauma to the eye does cause vitreous traction, it is not the most common cause of detachment. The force of traction is usually spontaneous but can be secondary to minor trauma or even caused by regular eye movement. In axial myopia, which is characterized by an increase in axial length, there is a greater tendency for peripheral vitreoretinal degenerative changes, such as lattice degeneration and atrophic holes, and thus a higher incidence of retinal detachment. Axial myopia is often characterized by a posterior staphyloma, a tilted optic disc with a temporal conus, and a high refractive error (–6.00 diopters or greater).

If detected early, holes or tears are generally treated using laser or cryotherapy. It is imperative that patients at risk for retinal breaks are screened regularly, including those with a family history of retinal detachment. A retinal tear may be detected at a routine eye assessment ( Fig. 24.7 ). Common visual symptoms include spontaneous flashes of light that are often described as camera or lightening-like, or a sudden increase in floaters. The floaters are usually caused by the breakdown of vitreous humor into linear strands that become visible to the patient but can more rarely be caused by small broken blood vessels that liberate free red blood cells, which, in turn, cast shadows on the retina. Retinal detachment in asymptomatic patients is most often detected later as compared with patients who display symptoms early. At the onset of retinal detachment, patients will experience a persistent shadow in their visual field that slowly expands in the affected eye. A nonrhegmatogenous retinal detachment occurs in the absence of a retinal hole. This can be a result of inflammation, or in more sinister cases, from an ocular malignant melanoma.

Retinal detachment. Note folding of the retina, which is in focus anteriorly.

A retinal detachment warrants immediate repair, especially in the case of macula-on retinal detachment. There are various surgical approaches to repairing retinal detachment depending on the pathology and mechanism, but the most common approaches include pars plana vitrectomy to relieve any vitreous traction, or, as mentioned previously, laser or cryotherapy to seal off the offending hole or tear. Sometimes, a scleral buckle may be necessary to indent the globe to bring the detached tissues into close proximity, and to reduce tractional forces. The liquefied vitreous that has accumulated beneath the retina is often drained during surgery so that the retina will lie flat. Most retinal detachment repair procedures are successful with good visual prognosis (over 90% of routine cases) when patients present early, before the macula becomes involved. If the macula becomes detached (“macula off”), a reduction in postsurgical visual acuity is more likely to occur. An average of 6 to 12 months are required to obtain full visual recovery.

Central serous chorioretinopathy

Central serous chorioretinopathy (CSR) is a type of serous nonrhegmatogenous retinal detachment that involves the macula but is unassociated with a retinal tear or hole. Serous detachment of the macula is more common in males than in females and typically occurs in younger patients (25–50 years of age). There appears to be a strong positive correlation between CSR and stress, type-A personality trait, and steroid use.

Common symptoms of CSR include blurred and distorted vision with loss of color perception. Objects often appear curved, darker in color, and smaller (known as micropsia ).

Fluorescein angiography typically shows a leakage point in which fluid passes from the choroid through a defect in the RPE to a location beneath the retina. Most cases of CSR resolve spontaneously within 3 months and require no specific therapy. Treatment may be necessary in cases with prolonged visual loss or with signs of degenerative changes. Treatment options include laser photocoagulation to seal the defect in the pigment epithelium or photodynamic therapy (PDT) with good efficacy.

Changes in the retina from concussion

Foreign body in the eye

The degree of damage from an intraocular foreign body depends on the mechanical disruption of tissue, as well as the chemical composition of the foreign object within the eye.

Metals are one of the more common foreign bodies found in the eye, with most retained ocular foreign bodies being results of industrial accidents. Like with any object, the severity of a metal injury is dependent on the type and chemical nature of the metal. Gold, silver, platinum, aluminum, and glass are chemically inert and do damage only by traumatic disruption of the ocular tissue. On the other hand, a foreign body composed of relatively pure copper (greater than 90%) can cause massive inflammation. Copper in a concentration of 70% to 90% will cause chalcosis , with the deposition of copper in intraocular structures leading to cataracts and glaucoma. If the foreign body is an alloy of copper in a concentration of less than 70%, it will rarely result in any secondary intraocular problems.

A retained iron foreign body can cause siderosis bulbi . Iron is toxic to the retina and other ocular tissues. Intraocular foreign body containing iron should be removed to prevent sensory retinal toxicity and profound loss of vision as indicated by a flat or extinguished ERG. The trabecular meshwork can also be affected, which can result in glaucoma. These changes can be observed from months to years after the accident. If the foreign body is removed at an early stage, the entire process of siderosis bulbi may be prevented.

Metal injuries are common. Fortunately, metallic foreign bodies are magnetic, making their surgical removal somewhat easier. The best treatment, however, is prevention, which means the use of polycarbonate safety goggles or facemask if any risk is perceived.

Solar retinopathy

Direct sun gazing or looking directly at an eclipse, even if only for seconds, can result in a macular burn. Burned maculae will appear mottled with subtle RPE changes after the initial injury. With time, a macular hole can form, resulting in permanent damage to vision.

There is no absolute safe way to protect children against such mishaps. The best treatment is prevention. Preventative measures include abstaining from sungazing, avoiding playing with laser devices, or exercising caution in viewing an eclipse by wearing proper eye protection. Because children are most prone to participation in these activities, there can be no guarantees of patient compliance.

Age-related macular degeneration

AMD is the leading cause of severe central vision loss in people over the age of 50 years in developed nations. The risk of developing some form of AMD increases with age and, by age 75 years, the risk approaches 40%.

There are two types of AMD: dry AMD (85%–90%) and neovascular (wet) AMD (10%–15%). Severe visual loss from AMD usually occurs in the latter form AMD. With increased life expectancy, the number of patients with visual impairment from AMD is projected to increase by more than 50% over the next decade.

Classification

Early AMD: this stage is defined by the presence of numerous small (<63 microns) or a few intermediate (63–125 microns) drusen.

Intermediate AMD: characterized by the extensive drusen of small or intermediate size, or any large drusen (>125 microns). The average diameter of a retinal vein on the optic disc margin is 124 microns.

Advanced AMD: this stage is characterized by the presence of either geographic atrophy, or presence of choroidal neovascular membrane (CNVM; i.e., wet AMD). The latter can lead to sequelae, such as sub-RPE bleeding, subretinal or sub-RPE fluid, and subretinal fibrosis or scarring).

Disciform degeneration of the macula ( Fig. 24.8 ). If serum or blood leaks into the macula, the healing process can lead to gliosis, which leaves a flat grayish-white scar. This scar results in permanent loss of central vision, whereas the peripheral field of vision is left intact. Degenerative changes can also occur if the pigment epithelium undergoes atrophy, which leads to death of the photoreceptors and a decrease in vision.

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