Gallemore's Corner
Ron Gallemore, M.D.
December 2014
Optical Coherence Studies: What to look for and when to refer
Many optometric practices now have OCT capability or utilize other practices to obtain the tests. Either way, understanding what to look for and when to refer can be a daunting task. Here are some of the basics:
Normal OCT: There is a surprising amount of variation in a normal OCT. On average, the foveal thickness is about 250 microns. In younger patients the normal thickness can be greater and in older patients less by 25-50 um! High myopia will reduce the thickness as the retina is stretched and hyperopes may have a somewhat thicker retina. If there is good symmetry between the two eyes and you can explain extra or less thickness by one of the above the study is likely normal.
Epiretinal Membranes: This is the most common finding I get questions about. An ERM is seen on the surface of the retina and can reduce the foveal depression or even turn the fovea into an elevation instead of a dip. Often the two eyes are asymmetric. As a rule, these require a work-up. There can be an associated retinal tear or detachment, posterior uveitis, or vascular occlusion. An OPTOS image can help rule some of this pathology out but when in doubt, refer for a check, particularly if patient is symptomatic.
Vitreomacular traction and adhesion: Many patients have VMT or VMA, particularly myopes. If the foveal thickness is changing over time or the patient is symptomatic with metamorphopsia or new floaters, then a consult is in order.
Macular holes versus pseudoholes versus lamellar holes: Advanced macular holes are easy to diagnose but the early stages can be more challenging. Stages 1a and b and early stage 2 can be associated with no defect or a very small even eccentric defect, respectively, that may be missed if the right cross section is not performed. Referral is indicated.
Retinal Vein occlusions: Most RVOs can readily be seen with sector or diffuse hemorrhages in BRVO and CRVO, respectively. Cystic macular edema is often present. OCT shows asymmetric edema in RVO. In chronic, non-ischemic cases, there may be a relatively normal appearing fundus (hemorrhages have resolved) with occult macular edema. Check the BP in these cases and refer.
Macular Degeneration: Dry AMD with drusen presents with bumps along Bruch’s membrane. Subtle irregularities can be seen when the fundus exam appears normal. When atrophy is present there is collapse of the outer segment layer with thinning and a reflected signal that penetrates the choroid. Wet AMD is associated with edema in the retina that can be hard to distinguish from other disorders. If a patient is symptomatic or there is edema, referral is warranted. Screen any AMD patient with symptoms.
Central Serous: CSR presents with the classic dome like blister in a younger patient under stress or with a history of steroid use (Flonase, creams, joint or back injections, inhalers, testosterone gel and oral prednisone are common precipitants). The risk is missing wet AMD or uvieits (esp. Harada’s disease) so referral is indicated. Of note, any cystic edema in the retina argues against simple CSR. Once the diagnosis is confirmed, you can monitor and refer back should the need arise.
OCT is a powerful tool that sometimes opens a bag of worms. Understanding what to look for will keep you calm and collected when you see a bump or depression that doesn’t seem normal.
Ron P. Gallemore, M.D, Ph.D.
Founder and Director
Retina Macula Institute and the
Retina Macula Research Center
South Bay 310-944-9393
Downtown 323-464-9393
Many optometric practices now have OCT capability or utilize other practices to obtain the tests. Either way, understanding what to look for and when to refer can be a daunting task. Here are some of the basics:
Normal OCT: There is a surprising amount of variation in a normal OCT. On average, the foveal thickness is about 250 microns. In younger patients the normal thickness can be greater and in older patients less by 25-50 um! High myopia will reduce the thickness as the retina is stretched and hyperopes may have a somewhat thicker retina. If there is good symmetry between the two eyes and you can explain extra or less thickness by one of the above the study is likely normal.
Epiretinal Membranes: This is the most common finding I get questions about. An ERM is seen on the surface of the retina and can reduce the foveal depression or even turn the fovea into an elevation instead of a dip. Often the two eyes are asymmetric. As a rule, these require a work-up. There can be an associated retinal tear or detachment, posterior uveitis, or vascular occlusion. An OPTOS image can help rule some of this pathology out but when in doubt, refer for a check, particularly if patient is symptomatic.
Vitreomacular traction and adhesion: Many patients have VMT or VMA, particularly myopes. If the foveal thickness is changing over time or the patient is symptomatic with metamorphopsia or new floaters, then a consult is in order.
Macular holes versus pseudoholes versus lamellar holes: Advanced macular holes are easy to diagnose but the early stages can be more challenging. Stages 1a and b and early stage 2 can be associated with no defect or a very small even eccentric defect, respectively, that may be missed if the right cross section is not performed. Referral is indicated.
Retinal Vein occlusions: Most RVOs can readily be seen with sector or diffuse hemorrhages in BRVO and CRVO, respectively. Cystic macular edema is often present. OCT shows asymmetric edema in RVO. In chronic, non-ischemic cases, there may be a relatively normal appearing fundus (hemorrhages have resolved) with occult macular edema. Check the BP in these cases and refer.
Macular Degeneration: Dry AMD with drusen presents with bumps along Bruch’s membrane. Subtle irregularities can be seen when the fundus exam appears normal. When atrophy is present there is collapse of the outer segment layer with thinning and a reflected signal that penetrates the choroid. Wet AMD is associated with edema in the retina that can be hard to distinguish from other disorders. If a patient is symptomatic or there is edema, referral is warranted. Screen any AMD patient with symptoms.
Central Serous: CSR presents with the classic dome like blister in a younger patient under stress or with a history of steroid use (Flonase, creams, joint or back injections, inhalers, testosterone gel and oral prednisone are common precipitants). The risk is missing wet AMD or uvieits (esp. Harada’s disease) so referral is indicated. Of note, any cystic edema in the retina argues against simple CSR. Once the diagnosis is confirmed, you can monitor and refer back should the need arise.
OCT is a powerful tool that sometimes opens a bag of worms. Understanding what to look for will keep you calm and collected when you see a bump or depression that doesn’t seem normal.
Ron P. Gallemore, M.D, Ph.D.
Founder and Director
Retina Macula Institute and the
Retina Macula Research Center
South Bay 310-944-9393
Downtown 323-464-9393