Peripheral Retina Lecture
You must have a good understanding of the anatomical location of the peripheral retina structures and their relationship to one another. The peripheral retina is defined as the zone from the equator to the ora serrata and is approximately three to four disc diameters (3DD-4DD) in width.
ANATOMICAL STRUCTURES OF THE RIGHT EYES PERIPHERAL RETINA
The vortex veins and ampullae will serve as very good landmarks for an examiner. These vortex ampullae and veins represent the equator of the eye. They are very important when one wants to describe retinal defects and their relationship to the rest of the retina. Vortex veins and ampullae are usually very easily seen in fair complexioned, light hair and blue eyed individuals. However, they might blend in with the rest of the retinal pigment background making them more difficult to delineate. There is always some pigment migration, in these cases, toward and around the vortex ampullae and in these cases the pigment migration is the only clue to the vortex ampullae location.
The long ciliary nerves are your two horizontal landmarks located at three and nine o'clock. They have a broad base located at the ora and taper to a somewhat rounded apex approximately at the equator. The short ciliary nerves are most visible in the superior and inferior peripheral retina and usually located very near one of the vortex veins and ampullae. They may run all the way to the ora or only be seen as a very short whitish to yellow colored structure that definitely stands out from the rest of the retina
The ora serrata is the point where the choroid and retina end. The ora will vary in color from black, brown to a felt soft gray. It is not uncommon to find the retina near it to have a slightly off colored orange gray appearance known as chorioretinal degeneration. This can be broken down in to mild, moderate, and severe degeneration. Regardless how one classifies the degeneration there is little to worry about and is considered to be benign with no predisposition to retinal holes or tears
The pars plana, when first seen, is very confusing because in many patients it looks very much like the rest of the retina in color. It is usually noticed while looking at the ora serrata and the degeneration near the ora. Suddenly one finds themselves trying to determine what they have just discovered. One moment the pigmented ora is seen then what appears to be normal colored retina jumps into view. It must be pointed out that you will not see this structure in every patient unless the pupil is dilated maximally.
It is essential that everyone realizes the primary reason for performing a dilated examination of the peripheral retina is to detect potential retinal detachments (RD). There are of course other findings a dilated retinal examination can reveal, but RD are the primary reason. Retinal detachments constitute a separation of the sensory retina from the underlying retinal pigment epithelium, (RPE) due to the accumulation of liquefied vitreous fluid in that potential space. Most RD are the result of one or more retinal holes that allow passage of fluid between the sensory retina and the RPE. The RD may be quite flat or become large and bullous protruding into the vitreous cavity and undulate with eye movements. The bullous detachment is an active detachment with sloping visual field margins. Detachments may occur anywhere in the retina where a hole or tear is located. Superior detachments are potentially more serious than inferior ones because of gravity. They may rapidly extend inferior to detach the macula with loss of central vision which may be permanent, even if surgery is successful in restoring the retina to its proper position. Older or small incomplete RD will leave a pigmented line along their borders. These flat peripheral RD if suspect must be sclerally indented to differentially them from a flat retinoschisis. Dr. James Hunter refers to these pigmented (demarcation) lines as danger lines. If not correctly diagnosed an the patient later develops a RD the doctor is in danger of being sued.
Symptoms associated with a RD may be minimal to no symptoms at all. Frequently the patient complains of light flashes, dark floating specks, and a curtain-like defect in their field of vision. Patients with these complaints must be seen promptly. Most retinal detachments are associated with retinal holes and the holes, in turn, are the result of vitreous traction. Vitreous traction may cause a classic horseshoe tear or retinal break making the patient more predisposed to developing a retinal detachment.
BENIGN PERIPHERAL RETINA FINDINGS
1.) It is common to fine cystoidal degeneration near the ora serrata. It is found in most all adult eyes and increases with age. Though considered to be benign by itself it is involved with some other conditions that are not so benign. These will be discussed later (retinoschisis ).
2.) Pavingstone or Cobblestone degeneration is found in about 27% of the population. It is considered by some not to be a degeneration but a retinal defect that has been present since birth. Though the retina appears atrophied the condition is more like that of a coloboma or failure of that part of the retina to develop. It is most often found in the inferior-temporal part of the retina between the ora and the equator. Dr. Alexander, however, classifies this as a degeneration seen in patients over the age of 20 years.
3.) Reticular pigmentary degeneration is a common finding in the peripheral fundi of older patients. When these areas are indented one usually finds an area of honeycomb degeneration present deeper in the retina.
4.) Equatorial drusens are another common finding that is very interesting and are usually only note worthy. They are usually of the soft fluffy type and as long as they do not involve the macula foveal area they seldom cause vision problems. What are drusens? The RPE functions in several ways. It forms an outer blood-retina barrier, works in the transport of metabolites between the choriocapillaris and the retina, functions to eliminate damaged and discarded photoreceptor outer segments and works to prevent the development of choroidal neovascular nets. When the RPE cells are not functioning properly they produce an extracellular material such as collagen an basement membrane material, which is deposited onto Bruch's membrane. The resulting deposits are called drusens which are composed of mucopolysaccharides and lipids. One might think of drusens as kind of garbage dump resulting from a not too healthy RPE. Drusens of some form are found in over 70% of patients over 50 years and do not negatively affect all eyes.
5.) Choroidal or pigmentary degeneration, are one and the same and is located at or near the ora. Another peripheral retinal condition that is only note worthy.
RHEGMATOGENOUS PERIPHERAL CONDITIONS
1.) Lattice degeneration, (Non-pigmented & pigmented lattice) holes within this degeneration are the result of extreme thinning of the retinal tissue.
Pigmented lattice like degeneration aligned with a peripheral vessel.
· A.) Retinal erosion (non-pigmented)
· B.) Snail track (non-pigmented) with holes and tears
2.) Retinoschisis - bullous & flat
· A.) Acquired or Reticular schisis
· B.) Congenital or Typical Schisis
3.) White Without Pressure
4.) Vitreoretinal Adhesions (Retinal Tag)
5.) Snowflake Vitreoretinal Degeneration once was thought to be a benign finding. However, recent findings classify it as an inherited condition which may be related to retinitis pigmentosa. The retinal layers involved included the inner retinal layers. The condition progresses through four stages and may develop retinal breaks, retinal detachments, or neovascularization of the peripheral retina may occur.
Rhegmatogenous means to tear or break. In these cases it is related to retinal areas of degeneration that may develop tears, breaks or holes leading to retinal detachments. The reason dilation and peripheral retinal examinations are so very important is detecting conditions that may lead to retinal detachments or patients who have retinal detachments. It is somewhat surprising that about 50% of all patients with retinal detachments are totally asymptomatic.
Detachments not secondary to a retinal holes tears or breaks are called nonrhegmatogenous detachments and are caused by primary choroidal tumors, inflammation, or metastatic lesions. The tumors that commonly produce these "secondary" detachments are choroidal melanomas or metastatic carcinomas from the breast, lung, and prostate which migrate to the choroidal vascular system.
LATTICE DEGENERATION: The clinical appearance is that of circumferentially oriented, sausage-shaped areas. Located at or between the equator and the ora serrata, of increased atrophic thinning retina and increased retinal pigment epithelium (RPE) pigmentation. The vitreous over lying this area is liquefied and the vitreous membrane is firmly attached. Radial white (lattice) lines represent sclerosed retinal vessels and along with these may be overlaying vitreoretinal (glitter). The majority of the lesion has a grayish white appearance. Holes which occur within lattice areas are either the result of continued thinning of the retinal tissue or secondary to vitreoretinal adhesions which are associated with the lesion. Tears occur as a result of vitreoretinal adhesions and traction at the borders of the primary lesions. Tears and holes have a deeper reddish color than the surrounding lesion or retina which helps make a differential diagnosis.
Other atrophic equatorial retinal changes are "retinal erosion" and "snail tracks" which are grayish in color and most likely variations of lattice degeneration. They do lack the pigmentation, but have many of the other characteristics of lattice degeneration. A very good term for these areas of atrophy is "lattice like" degeneration".
RETINOSCHISIS: There is a congenital "flat"("typical" according to Dr. Alexander, probably to differentiate it from Congenital Hereditary Retinoschisis) retinoschisis which is the splitting of the nerve fiber layer at the outer plexiform layer. Dr. Alexander believes the "flat" schisis represents an advanced form of cystoid degeneration. Then there is the acquired "bullous" ("reticular" according to Dr. Alexander) form of retinoschisis. The acquired form if not the most common is certainly the most eye-catching looking like a water blister protruding inwardly toward the inside of the eye. Some believe it is actually a complication occurring secondary to peripheral cystoid retinal degeneration. Clinically, degenerative acquired retinoschisis appears as a ballooning "bullous" retinal elevation with smooth sharp borders. The cavity of "bullous" schisis is thought to be filled with hyaluronic acid a mucopolysaccharide. Hyaluronic acid is typically very viscous, a component of the vitreous, which would explain the taut appearance of the schisis. The condition is the result of splitting of the inner limiting membrane and the outer nuclear layer of the retina. The neuroepithelium remains intact, but the inner layer becomes stretched and thinned because of the vitreous traction. Vitreoretinal "glitter" which is sometimes referred to as "snowflakes" and sclerosed whitish colored retinal vessels are found on its inner surface. These vessels give it a reticular appearance and are common findings on the inner layer. Retinal holes or breaks may occur in either the inner or outer layers; holes in just the inner layer are basically note worthy, while holes in the outer layer are of greater concern, e.g., retinal detachments are more likely. Superior bullous retinoschisis with inner and outer layer breaks or a schisis that is already posterior to the equator should be referred for a second opinion. Because of the splitting of the retina the field defects are absolute and have steep borders. Bullous retinoschisis do not undulate (wave) with eye movements like a retinal detachment. Holes in the inner layer are not treated because they are simply openings into the cystic cavity, but outer layer holes may require treatment, since they could facilitate the formation of a retinal detachment. Cases with holes in both layers should be referred for consultation and possible treatment.
VITREORETINAL ADHESION (RETINAL TAG): These are areas of atypical retinal tissue to which the vitreous membrane has become firmly attached. The condition may be either congenital or acquired, in that the atypical retinal tissue may have been present from birth or resulted from a small area of inflammation or trauma. With vitreous age changes, the vitreous body liquefies and shrinks, causing a strong physical tugging on this area of retina. Two things may happen, either a small plug of retina will pull free releasing the physical tension or the retina will tear. If a plug of retina pulls free releasing the tension the likelihood of a retinal detachment is very small. However, if the retina tears the odds of a retinal detachment then or in the future are greatly increased. These areas should be monitored every 2 months, then 4 months and every 6 months, however, tears should either be referred or monitored more closely. Photographs of these areas are a great aid in monitoring patients.
Patient education in all rhegmatogenous cases is a must . It is extremely important and should always be recorded in the patients record that the patient has been educated regarding symptoms associated with RD. Also, record when you want to see them again then followed this up with a recall card. Patients should be told to return anytime they experience any visual changes; increased number of floaters, spots, flashes of light, veil like curtain affecting peripheral vision or any change of concern.
In the event of any of these symptoms and negative dilated fundus examination findings you must always check for "Shafer's Sign". The presence of pigment granules in Berger's space or anterior vitreous indicates there is a retinal break or detachment. Pigment granules may be present if the patient has had previous ocular surgery, but you cannot allow that to influence the need to go back and take another look.
Dr. James E. Hunter conducted a peripheral retina study on 1000 patients. All patients were dilated and B.I.O. examinations performed. The break down of the 1000 patients is as follows:
Caucasians = 692
African Americans = 308
1.) Lattice degeneration (all types)
· Present in 3.5% of the Caucasians
· Present in 7.0% of the African Americans
2.) Retinoschisis (all types)
· Present in 0.5% of the Caucasians