Is it normal? Peripheral retinal findings--Part 1.
The rod-dense peripheral retina is the portion of the retina located anterior to the equator and extending to the ora serrata, which is where the retina and choroid end. The peripheral retina thins gradually as it approaches the ora serrata to about 0.12mm (parafoveal retina measures 0.23mm thick) making it more susceptible to tears and breaks. (1) The functions of the peripheral retina are many and primarily include dim light/ scotopic vision, slow moving object perception, black and white vision, and peripheral visual field extent.
To obtain a clear, full, in vivo view of the peripheral retina, your patient should be dilated, followed by thorough examination with binocular indirect ophthalmoscopy and a 20.00D condensing lens and possibly scleral depression.
A three-mirror contact lens using the trapezoid mirror also gives a clear view of the peripheral retina in a dilated patient. Furthermore, the advent of new imaging technologies, such as Optomap, provides a wide view of the peripheral retina and is useful for documenting peripheral retinal lesions. Be aware, however, that many of these new imaging technologies do not show the full extent of the far peripheral retina: Optomap, for example, images 82.5% of the retina. (2)
On indirect examination, vortex veins and ampullae serve as useful landmarks to demarcate the equator and the start of the far peripheral retina, which then extends anteriorly to the ora serrata, which appears as a greyish black textured band.
The peripheral retina is exciting because so many interesting diseases and degenerations happen in this area. For the examiner the challenges are to differentiate normal from abnormal and to appropriately manage the patient. This two-part series will focus on several common peripheral retinal findings providing a description, clinical appearance, and how to manage each case. The degenerations are considered by type: retinovitreal degenerations involve the interface between the retina and vitreous; chorioretinal degenerations occur between the retina down to the choroid; and intraretinal degenerations, covered in the second installment of the series, involve the retina itself.
Some miscellaneous common peripheral retinal findings are also discussed. Finally, a brief discussion of retinal detachment will be covered.
Please note that all images have been magnified to highlight the peripheral retinal finding and thus the lesion may appear closer to the fovea than in actuality.
Lattice degeneration is one of the most commonly seen peripheral retinal conditions, occurring in 6-10%' of the general population and is usually present by the second decade of life. (3) Both environmental and genetic factors seem to play a role in its development, including a recently identified gene region.3 Lattice degeneration is bilateral in 33-50% of cases and occurs more commonly in myopes, particularly those with long axial lengths. (4,5) There is no racial or gender preference. (6) It appears as an oval or circumferential area of retinal thinning, which has overlying vitreous liquefaction. Criss-crossing thin white sclerotic vessels give the characteristic appearance of latticework, hence its name. It may also be associated with retinal pigmentation and whitish-yellow surface spots or flecks (see Figure 1).
Lattice degeneration is an area of retinal thinning that is associated with atrophic holes in 25% of cases, (7) and potentially with increased risk of retinal detachment (RD) as the posterior vitreous pulls on the borders of the atrophic, thinned retina. (6) The risk of RD remains less than 1% over an average of eleven years if no RD has occurred in the other eye.1 In cases of RD in the fellow eye, risk of RD increases to 2-5% over seven years. (8) The presence of atrophic holes does not increase the risk of RD. (6)
The decision to treat or not to treat lattice degeneration prophylactically to prevent RD is complicated. If the patient presents with symptoms of RD treatment is almost always indicated. However, in the absence of symptoms, prophylactic treatment is controversial and is not supported by robust evidence. (8) While the risk of RD remains low, cases that do develop this complication show variable amounts of lattice degeneration: in one study, 30% of phakic RDs had lattice degeneration present; (8) in the Scottish retinal detachment study, 18.7% of the eyes experiencing RD had lattice degeneration.9 Patients with risk factors for RD such as long axial length, aphakia, or a history of RD in the fellow eye may strengthen the argument for prophylactic treatment. (6)
If prophylactic treatment is elected then it is usually performed in one of two ways: transconjunctival cryotherapy employs a very cold probe that is applied to the conjunctiva to freeze the retina and is used for more anterior lesions; laser photocoagulation uses a high energy beam through the ocular media for more posterior lesions.
Both methods create points of adhesion surrounding the retinal breaks to prevent the flow of fluid (see Figure 2). (8) Both forms of treatment create scotomas in the areas of scarring and have inherent risks including new tears, RD, infection, and haemorrhage.
Patients with lattice degeneration should be informed of your findings, educated about the symptoms of RD, but reassured that their chance of developing this complication is extremely low. Re-emphasise that if symptoms of RD begin, then the patient is to return to clinic immediately and not simply to wait until their next scheduled visit. The clock-hour location and size and location of lattice including the number of atrophic holes, if present, should be documented.
Snail track degeneration
Snail track degeneration occurs circumferentially in the peripheral retina and appears as chains of whitish radiant dots consisting of microglia and astrocytes. (1) Presenting most often in young, myopic eyes, it may be a precursor to lattice degeneration although its incidence does not increase with age. (10) Similar to lattice, snail track degeneration may have associated atrophic holes that develop in the areas of thinning. Asymptomatic lesions do not require referral or treatment in the absence of high-risk characteristics, which include high myopia, aphakia, history of RD in the fellow eye, or strong family history of RD. (7)
Snowflake degeneration is a vitreoretinal degeneration characterised by early onset cataract, severe fibrillary vitreous degeneration causing an optically empty vitreous, peripheral vascular sheathing, degenerative atrophy of retinal pigment epithelium, and peripheral retinal abnormalities consisting of minute shining intraretinal crystalline-like deposits that resemble snowflakes. (11) The term for the disease was first coined after a family presented with these unique characteristics. The disease progresses through four stages with the end stage characterised by the disappearance of peripheral retinal vessels. (6) Patients often have symptoms of floaters and decreased VA due to early onset cataract, although most maintain VA of better than 6/18 with close care. (11) About 20% of patients experience RD, typically in their sixties. (11)
Snowflake degeneration is included in the spectrum of diseases with Wagner and Stickler syndromes, however, it is clinically and genetically unique. (12) Snowflake degeneration is transmitted in an autosomal dominant fashion and is associated with a mutation in the potassium channel KCNJ. (13) Additional clinical features include corneal guttata resembling those in Fuchs' endothelial dystrophy, and flat-appearing optic discs with waxy pallor, occasionally dysmorphic in shape, and situs inversus of the central retinal vessels, differentiate snowflake degeneration from other conditions in the spectrum. (6,11)
Wagner syndrome may further be differentiated from Snowflake degeneration by its alternative genetic mutation (in CSPG2), more pronounced chorioretinal atrophy, nyctalopia, pseudoexotropia from the congenital temporal displacement of the fovea, and poorer end visual outcome. (12)
Stickler syndrome (I and II) may be differentiated from Snowflake degeneration by the presence of systemic associations, namely hearing loss, cleft palate, midface hypoplasia, and arthropathy. (12) The genetic mutations occur in COL2A1 and COL11A12. Additionally, the retinal findings in Stickler syndrome often include radial lattice and a higher rate of RD. (6)
While prophylactic treatment is not recommended for any of these degenerations, patients with suspected Snowflake degeneration, Wagner, or Stickler syndromes should, nevertheless, be initially referred for evaluation to classify their disease and for genetic testing. Family members should be screened due to the hereditary nature of these diseases.
White with pressure and white without pressure
White with pressure (WWP) appears as a milky white opalescent area that obscures the underlying choroid during the use of scleral depression. (14) The underlying retina returns to normal appearance without indentation. WWP occurs in up to 35% of normal eyes but its cause is poorly understood. (15)
White without pressure (WWOP) is a similar phenomenon that occurs without scleral depression and is also of controversial origin. (15) WWOP occurs in up to 30% of the general population with increased incidence in blacks, (16) myopes, (5) and with advancing age (14) Often bilateral, WWOP appears as a whitish area that may have scalloped borders and/or be bounded posteriorly by a reddish-brown line (see Figure 3). WWOP is migratory in nature and can be found in all quadrants of the peripheral retina. (17)
As WWOP may indicate increased vitreoretinal adhesion and traction, potentially there could be an increased likelihood of RD although this relationship has not been established. (18) Patients should be followed routinely and educated about the symptoms of RD.
CHORIORETINAL DEGENERATION Pavingstone (cobblestone) degeneration
Pavingstone, or cobblestone, degeneration occurs in 22-27% of the general population and is bilateral in 33% of cases. (7) Increased incidence occurs with age, (7) and with longer axial length in myopia. (45) Pavingstone degeneration appears as round, discrete yellow-white spots about one half to two disc diameters in size often with pigmented borders of hypertrophic RPE (see Figure 4); it is found adjacent to the or a serrata, most commonly in the inferior quadrant.
The pathophysiology consists of areas of retinal pigment epithelial and choroicapillaris atrophy and loss followed by subsequent adherence of the thinned retina to the choroid. (7) Thus, the presentation can be dramatic as the sclera is partially visible through the atrophic areas with often large choroidal vessels visible at the base.
Normal vitreous and choroid overlies the area of pavingstone so while the appearance can be dramatic, there is no association with RD. Neither referral nor treatment is needed but simply documentation of location and size.
MISCELLANEOUS Retinal tuft
Retinal tufts are internal projections of retinal tissue located at the area of the vitreous base. They are classified as noncystic, cystic, or zonular traction. (6) Noncystic tufts are common, occurring in about 72% of patients. Noncystic tufts are thin, short internal projections that are continuous with the vitreous and have a narrow base of less than 0.1mm. There is no association with retinal break or detachment.
Cystic retinal tufts are also common, occurring in 59% of patients, and are probably congenital as they have been noted in newborns. (6) Cystic tufts have a base of attachment that is greater than 0.1mm in diameter, may have associated pigmentation, and often have condensed strands of vitreous attached to the apex. They appear as chalky-white discrete sharply demarcated round or ovoid cysts with abnormally condensed vitreous attached to the apex. (19) In a consecutive series of hundreds of RD cases, cystic retinal tufts were causally associated with RD in 6.5% to 7.5%; (19,20) the majority of these tufts located in the equatorial region. (19) Using that data, Byer computed the risk of cystic retinal tuft leading to RD as less than 1% (in the range of 0.18-0.28%) and thus prophylactic treatment is not indicated. (6,20)
Zonular traction tufts are found in 15% of eyes and are thin strands of retina that extends at an acute angle from the peripheral retina.
These may rarely be related to RD if located more posteriorly. (6)
Senile reticular pigmentary degeneration
Senile reticular pigmentary degeneration is a common finding in up to 20% of people over 40 years of age and increasing incidence with age. (21) It is almost always bilateral. The changes appear as linear patterns of hyperpigmented lines, which may have some branching, formation of incomplete patterns or polygons, or complete polygons with marked pigmentation located in the equatorial region to the ora (see Figure 5). (22) The aetiology is from degeneration of RPE cells and is associated with longer axial length in high myopia. (4) It may also be a marker for genetic susceptibility of age-related macular degeneration (AMD) in patients with or without signs of AMD. (22)
As an aside, the term tapetoretinal degeneration may appear in a literature search for reticular degeneration. The difference is that tapetoretinal degenerations are hereditary, primary, progressive and generally premature changes in a retina that previously showed normal development; the term is usually associated with disease processes such as Leber's congenital amaurosis, retinitis pigmentosa, and punctate retinitis. (23)
Senile reticular degeneration in itself is common and benign. Look closely for signs of AMD in these patients, but otherwise, no further treatment or testing is warranted.
Peripheral retinal drusen are yellowish, round hard or soft drusen located near the equator and are usually small to medium sized. (22) The RPE may build up around the edges of the drusen to give a pigment ringed appearance. The drusen are waste products of RPE cells that are then deposited into the basal lamina. Peripheral drusen are present in eyes with and without AMD although there is a two-fold risk of peripheral retinal drusen among individuals with intermediate and advanced AMD. (22) Current studies focused on the genetic similarities of AMD, senile reticular degeneration, and peripheral drusen have established that there are indeed genetic crossovers. (22)
Like senile reticular degeneration, peripheral retinal drusen are a benign and a common finding that need no further follow-up, except for AMD monitoring.
MAKING SENSE OF WHAT YOU FIND
An excellent clinician must first see these peripheral retinal lesions, then properly classify the lesion, and finally know whether or not to refer the patient. Almost all of the conditions in this article are benign and need not to be referred if correctly identified, thus saving your patient time, potential expense, and possible worry. The old adage, "if in doubt, then send it out," however, is true and so if uncertain then these patients should be referred along the appropriate pathway.
The second installment in this series will consider CHRPE, intraretinal degenerations and a brief discussion of retinal detachments.
ABOUT THE AUTHOR
Dr Kate Lanier is a clinical instructor at Anglia Ruskin University and author for KMK Continuing Education. She completed a primary care/ ocular disease residency at the W.G. (Bill) Hefner VA Medical Center hospital in the US and worked in a medical-model private practice in North Carolina.
Dr Kate Lanier OD, FAAO
Course code: C-40213 Deadline: May 2, 2015
To be able to explain the clinical relevance of peripheral retinal degenerations to patients (Group 1.2.4)
To understand the appropriate methods for examining the peripheral retina (Group 3.1.3)
To be able to recognise peripheral retinal degenerations (Group 6.1.5)
To be able to explain the clinical relevance of peripheral retinal degenerations to patients (Group 1.2.4)
To understand the methods used for examining the peripheral retina (Group 3.1.3)
To understand the clinical features of a range of peripheral retinal degenerations (Group 8.1.2)
To understand the natural progress for a range of peripheral retinal degenerations (Group 1.1.1)
To understand the appropriate methods for examining the peripheral retina (Group 2.1.2)
// REFLECTIVE LEARNING
Having completed this CET exam, consider whether you feel more confident in your clinical skills - how will you change the way you practice? How will you use this information to improve your work for patient benefit?
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|Title Annotation:||CET // PERIPHERAL RETINA|
|Date:||Apr 4, 2015|
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