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At Issue: Retinal Imaging
At Issue: posed the following question to a panel of experts: “Would you recommend that a posterior subspecialist purchase a retinal analyzer today, why or why not?”
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OCT use strongly recommended
Ugo Menchini, MD: I strongly recommend a posterior subspecialist to buy a retinal analyzer. I have been using optical coherence tomography (OCT) for several years. I have no personal experience with the use of the retinal thickness analyzer instrument.
Today many publications are available on the use OCT in several macular diseases. I believe that OCT provides invaluable information in certain diseases such as diabetic macular edema (DME) and macular hole or pseudocysts retinoschisis.
It is now evident that vitreous traction can enhance DME. Ophthalmic surgeons can suspect a tractional component in eyes with DME when a glistening posterior hyaloid is seen: this is more frequent in eyes with proliferative diabetic retinopathy or prior panretinal photocoagulation. In some of these cases, the presence of partial vitreomacular detachment and traction can be imaged with OCT very clearly. Yet in others a taut, fully adherent preretinal membrane can be seen with difficulty and one can guess its presence from indirect signs such as irregularities of the retinal profile.
In these cases one should look carefully for small blebs of shallow detachment of the membrane from the retinal surface that prove its existence, since observing an attached posterior hyaloid exerting traction may be difficult with OCT. The present commercial device can identify vitreous traction as a predominant causal factor of DME in some eyes but not in all cases. I hope that the next-generation OCT will be able to solve this problem by means of a higher resolution.
I find that OCT can often change the clinical biomicroscopic impression in early-stage macular hole: what we used to call “stage 1” holes according to Gass’ classification may prove to be foveal pseudocysts with OCT. It can also provide the best follow-up after macular hole surgery.
Finally, OCT may be an emerging technology for the follow-up of photodynamic therapy (PDT) of choroidal neovascularization. When I evaluate the need for PDT re-treatment, my clinical decision is partly based on the finding of macular edema and detachment overlying the membrane. It has been reported that retinal thickness may decrease after PDT, so studies based on OCT could assess if measuring retinal thickness at various steps can be a guide to clinical decision.
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Valuable in treating macular disease
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Robert Morris, MD, and Donald C. Stephens III, MD: Yes, posterior subspecialists should purchase retinal analyzers today, assuming their economic analysis is “in the black” for these devices. If not, they should try to begin using such devices at a nearby academic center.
Currently available retinal analyzers are quickly becoming a valuable aid to optimal surgical treatment of macular disease in our practice. This includes laser treatment of diabetic macular edema and vitrectomy treatment of all surface macular disorders.
Various retinal analyzers are now available to precisely image retina/ epiretinal tissue and to measure retinal thickness (figure 1). The multifocal ERG can also provide an elegant, color coded display of retinal function (figure 2A, 2B).
In 1994, after proving that the internal limiting membrane (ILM) could be safely removed from the macula, we predicted (Ophthalmology 101:1, 1994) that all forms of traction maculopathy (macular pucker, macular hole, cellophane maculopathy, vitreomacular traction syndrome) might one day be treated by removal of the ILM. For us this time has already come. Our forceps technique video is available from the American Academy of Ophthalmology’s continuing education program, and our Fluidic Internal Limiting Membrane Separation (FILMS) technique will soon be available.
With the availability of ICG staining, ILM forceps and soon the FILMS cannula, effective and safe removal of all traction maculopathy is finally “within our grasp.” We must have similarly elegant, objective methods of precisely identifying traction maculopathy for which delayed or inadequate treatment will be accompanied by rapidly diminishing visual return. These analyzers can also help us plan and evaluate laser treatments for diabetic macular edema.
Considering the importance of central vision and the costs of therapy, these diagnostic capabilities should become routinely available and reasonably reimbursable.
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Important diagnostic modality
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George A. Williams, MD: I believe that OCT has emerged as an important diagnostic modality for a variety of vitreoretinal conditions. OCT has been instrumental in improving our understanding of the pathogenesis of macular holes. It is now apparent that macular hole formation begins with a perifoveal vitreous separation with a persistent vitreoretinal adhesion at the center of the fovea. Early hole formation is characterized by intraretinal changes consisting of a split within the retina.
OCT allows clinicians to accurately determine the transition between a stage 1 hole and a stage 2 hole. This distinction is often difficult or impossible to make on clinical examination alone. Interestingly, OCT has also been shown to be helpful in the postoperative evaluation of macular hole patients. Patients that have restoration of normal or near normal foveal architecture typically have excellent postoperative vision, where patients with evidence of abnormal foveal architecture, even in the presence of a closed macular hole, tend to have poorer visual outcomes.
We have also found OCT to be useful in evaluating diabetic patients with macular edema. A topographic map of retinal thickness throughout the macula can be generated to evaluate areas of macular edema. This is helpful in evaluating patients before and after laser photocoagulation. In patients with a taut posterior hyaloid and persistent macular edema, OCT may demonstrate a subclinical retinal detachment, as well as retinal edema. OCT is therefore useful in determining which patients may benefit from vitrectomy surgery.
OCT is useful in diagnosis of cystoid macular edema. Since it provides a quantitative measurement of retinal thickness, it may prove to be more valuable than fluorescein angiography for the diagnosis and management of this condition. As an additional benefit, it avoids the small but definite risk associated with intravenous injection of fluorescein dye.
Recently, Carmen Puliafito, MD, and colleagues at the New England Eye Center have demonstrated the utility of OCT in the postoperative management of patients treated with PDT. Although still preliminary, this work suggests that OCT can provide additional information that is helpful in determining whether or not patients require re-treatment. If this work is confirmed by larger studies, it may help to minimize some of the subjectivity inherent in the interpretation of post-PDT fluorescein angiography.
We have found OCT to be well tolerated by most patients. We have been able to perform OCT on children as young as 6 years of age.
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Limited application in daily practice
Jose Ma Ruiz-Moreno, MD, and Jorge L. Alio, MD: To date there is no clear and evident clinical indication for the use of retinal analyzers. A lot of studies have been published about the role of retinal analyzers in diagnosis of macular pathology; however, application in daily clinical practice is still limited.
It could be used as an investigative tool to study the changes that occur in the macular area in cases of macular hole, macular edema and exudation in cases of age related macular degeneration. It could also help us to clarify different aspects of the nature of these diseases to be added to other data obtained by other investigative methods.
In the future, when there is a way to establish these indications, the retinal analyzer could be part of the daily clinical practice. However, to date, its role is only complementary in diagnosis of cases of macular pathology.
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