Ординатура / Офтальмология / Английские материалы / Retinal and Vitreoretinal Diseases and Surgery_Boyd, Cortez, Sabates_2010

conditions. This can be very useful in following a patient with keratoconus or pellucid marginal degeneration. Even if the corneal topography is symmetric and central-ultrasound pachymetry is normal, the OCT pachymetry map can reveal an abnormal pattern of corneal thickness, raising suspicion for forme fruste keratoconus.

High-Resolution OCT Corneal Scan

Post LASIK procedures, high-resolution corneal scans detail the actual thickness of the flap and the residual stroma. This is useful in ensuring that enough residual stroma will remain after an enhancement.

Imaging of Abnormal Retinal

Structures

OCT can effectively distinguish lesions that ophthalmoscopically are difficult to identify and resemble various stages of macular hole development like lamellar macular hole, macular cysts, macular edema, sub-retinal hemorrhages, retinal and/or foveal detachments of neurosensory

retina or pigment epithelium, and epiretinal membranes with macular pseudoholes.

Enhanced Visualization of Macular

Holes

Comparing to biomicroscopical observations OCTgivesadditionalinformationaboutidiopathic macular holes, especially in their early stage. According to the literature, the foveal cystoid space or pseudocyst is considered the first step of full-thickness macular hole formation, instead of foveolar detachment as proposed by Gass(4,5). A foveal pseudocyst appears in the tomographic imaging as a large intraretinal cystoid formation that occupies the inner part of the foveola and disrupts the outer retinal layers. A foveal pseudocyst is considered a specific entity that may be the result of the incomplete separation of the vitreous cortex at the foveal center.

The role of the vitreous cortex in development of macular holes using OCT has also been clarified in various studies(6,7) (Figure 7). But the greatest advances obtained by OCT are in the field of vitreo-retinal surgery.

Indeed the ability of OCT to more accurately identify macular holes allows clinicians to better predict the surgical outcome. OCT reveals anatomic configuration of surgically closed macular holes within 24 hours after successful surgery(8).

Interesting results have been obtained by using OCT also in the study of retinoschisis, that is represented in the OCT as retinal splitting of the outer retinal layers in the macula, with inner retinal columnar structures that bridge the inner and outer retinal layers(9).

OCT has demonstrated that foveal retinal detachment and retinoschisis are common in severely myopic patients, with posterior staphyloma, while biomicroscopic observation revealed only a retinal detachment. Retinal detachment may precede the formation of a macular hole in severely myopic eyes(10).

Also, idiopathic posterior pole retinoschisis in highly myopic eyes is easily diagnosed by OCT and it is possible to establish the true extent of these macular changes(11).

In the presence of idiopathic macular membranes, OCT can give complementary information in the evaluation of anatomical features of the macula before and after surgical removal of the membrane.

The epiretinal membranes are identified by OCT when they are separated from the inner margin of the retina, and appear as a hyper-re- flective thin band anterior to the retina. When they are tightly adherent to the retinal surface they are identifiable by an increased reflective image on the retina (Figure 8). OCT, in distinction from other diagnostic methods such as ultrasound, can detect the presence of hidden retinal alterations, such as a cystoid macular

edema or a sub-foveal retina detachment, or a tractional macular hole. OCT examination has demonstrated that the thickness of the macula decreases after epiretinal membrane surgery.

Application of OCT in

Diabetic Retinopathy

Accurate longitudinal comparisons of serial OCT scans depends upon reproducibly locating the central fovea. In patients with central fixation each OCT scan is centered on the patient’s fixation such that the OCT scan passes through the central fovea. In patients with eccentric or imperfect fixation, the location of the fovea can be estimated from each OCT scan using a computer algorithm that searches for a focal minimum in total intraretinal reflectivity which typically coincides with the central foveal depression.

OCT can be considered a sensitive technique in the study of diabetic retinopathy for the early detection of retinal abnormalities and in

quantifying macular thickness after laser treat-

ment.(12,13)

By OCT it is possible to differentiate between cystoid and diffuse edema. In cystoid edema, low reflective spaces, divided by thin hyperreflective membranes, correspond to cystic spaces in the outer plexiform and inner nuclear layers. A large central cyst was occasionally noted to extend beneath the inner limiting membrane.Intraretinalfluidaccumulationcauses reduced optical reflectivity. In diffuse edema, an area of low reflectivity was present within the retina.

Significant differences in retinal thickness comparing patients with diabetic retinopathy and normals have been detected by OCT, even in absence of clinically significant macular edema. Also an increase in macular thickness in diabetics either without retinopathy and/or edema compared to controls has been demonstrated(14,15). OCT is also useful for evaluating and documenting macular edema and mapping it(16) (Figures 9 and 10).

After vitreous surgery for diabetic macular edema, best-corrected visual acuity improvement is greater in eyes with less preoperative increase in thickness of the neurosensory retina(17). Recently an OCT retinal thickness map has been developedtoprovidemoreprecisemeasurements of macular edema(18).

Age-related Macular

Degeneration

Severevisionlossinthisdiseaseistheresult of choroidal neovascular membrane formation. Choroidal neovascularization typically appears as either classic choroidal neovascularization (well delineated) or occult neovascularization (less well delineated).

A number of new pharmacologic approaches arebeingappliedtomaculardegeneration.Vision lossinage-relatedmaculardegenerationtypically results when choroidal neovascular tissue with or without concomitant hemorrhage and exudation into the fovea occur. The presence of hemorrhage, subretinal fluid or hard exudate under the fovea are usually detrimental to vision. The presence of choroidal neovascularization itself underneath the central fovea may likewise be detrimental to vision.

Optical coherence tomography, because of its high resolution capability, is able to image subretinal fluid, intraretinal thickening and sometimes choroidal neovascularization. As a result these capabilities, OCT may have utility in the assessment of new treatment modalities for age-related macular degeneration.

Cystoid Macular Edema (CME)

Ophthalmoscopically, CME appears as elevation or thickening of the central macula. Intraretinal cyst formation is often present. The area of retinal elevation often has ill defined borders both on ophthalmoscopy and clinical examination. The presence of media opacity and/or a small pupil, as is common in uveitic patients, may make determination of the presence and area of CME difficult.

The use of optical coherence tomography for the measurement of cystoid macular edema may be useful. Longitudinal measurement of either axial scans and/or topographic images as described for diabetic macular edema can be utilized. Additionally, the amount of media opacity and pupillary miosis in patients with uveitis will not likely interfere significantly with the images obtained by optical coherence tomography.

Pathological Macular

Disorders

In the presence of macular diseases, OCT has demonstrated several new findings that may help the interpretation of the pathophysiologic changes in various disorders.

In idiopathic juxtafoveolar retinal telengiectasis, OCT shows a hyperreflective band within the inner retina, and has demonstrated the presence of a small plaque, consistent with the hypothesis of Gass and Blodi, of an epithelial proliferation into the inner retina in some cases of retinal teleangiectasis(19).

In idiopathic polypoidal choroidal vasculopathy, OCT has demonstrated a serosanguineous detachment of the retinal pigment epithelium, suggesting that these lesions are situated beneath Bruch’s membrane and are covered anteriorly by both retinal pigment epithelium and Bruch’s membrane(20).

OCT is useful to establish the presence of cystic degeneration of the macula, when macular modifications are not noted clearly on biomicroscopic examination or fluorescein angiography, in patients with initial central serous chorioretinopathy, in patients with no specific serous retinal detachment, and in inflammatory diseases.

With recent advances in technology, a new generation of OCT devices is now been developed. This new OCT technology may achieve “in vivo” retinal imaging with less than 3 μm axial resolution. A higher longitudinal resolution may contribute to a better visualization of intraretinal structures and pathology and could increase the reproducibility, sensitivity and specificity for diagnosis of retinal and macular diseases.

References

1.Schuman JS, Pedut-Kloizman T, Hertzmark E, Hee MR et al. Reproducibility of nerve fiber layer thickness measurements using Optical Coherence Tomography; Ophthalmology 1996,103: 1889-1898.

2.Blumantal EZ, Williams JM, Weinreb RN at al. Reproducibility of nerve fiber layer thickness measurements by use of optical coherence tomography. Ophthalmology 2000; 107(12):2278-82

3.Baumann M, Gentile RC , Liebmann JM, Ritch R. Reproducibility of retinal thickness measurements in normal eyes using optical coherence tomography. Ophthalmic Surg and Lasers 1998; 29, 4: 280-285.

12.Azzolini C, Patelli F, Codenotti M, Pierro L, Brancato R. Optical coherence tomography in idiopathic epiretinal membrane surgery. Eur J ophthalmol 1999; 9.206-211

docyst as the first step in macular hole formation. A prospective study by Optical Coherence Tomography. Ophthalmology 2001; 108:15-22.

5.Azzolini C, Patelli F, Brancato R. Correlation between optical coherence tomography data and biomicroscopic interpretation of idiopathic macular hole. Am J Ophthalmol 2001 (In press).

6.Mori K , Abe T , Yoneya S . Domeshaped detachment of premacular vitreous cortex in macular hole development. Ophthalmic Surg Lasers 2000, 31 (3): 203-209

7.Chauhan DS, Antcliff RJ, Rai PA, Williamson TH, Marshall J. Papillofoveal traction in macular hole formation: the role of optical coherence tomography. Arch Ophthalmol 2000; 118(1): 32-8.

8.Kasura Y, Arai J, Akimoto M, Yoshimura N. Optical coherence tomography to confirm early closure of macular holes. Am J Ophthalmol 2000; 130:675-6

9. Azzolini C, Pierro L, Codenotti M , Brancato R . OCT images and surgery of juvenile macular retinoschisis. Eur J Ophthalmol 1997;7:196-200.

10.Takano M, Kishi S. Foveal retinoschisis and retinal detachment in severely myopic eyes with posterior staphyloma. Am J Ophthalmol 1999;128:472-476.

11.Menchini U, Brancato R, Virgili G, Pierro L Unilateral macular retinoschisis with stellate foveal appearance in two females with myopia. Ophthalmic Surg Lasers 2000;3:229-32.

cal coherence tomography of idiopathic macular epiretinal membranes before and after surgery. Am J Ophthalmol 2000; 130:732-739.

14.Schaudig UH, Glaeflke C, Scholtz F, Richard G. Optical coherence tomography for retinal thickness measurement in diabetic patients without clinically significant macular edema. Ophthalmic Surg Lasers 2000 31(3) 182-6.

15.Pierro L, Lattanzio R, Brancato R et al. Clinical evaluation of macular thickness in diabetic patients with Optical coherence tomography (OCT). Investigative Ophthalmol. Vis.Sci.(Suppl).1998, 39:469.

16.Rivellese M, George A, Soulkes D, Reichel D, Puliafito C. Optical coherence tomography after laser photocoagulation for clinically significant macular edema. Ophthalmic Surg Lasers 2000; 3:192-7

17.Otani T, Kishi S . Tomographic assessment of vitreous surgery for diabetic macular edema. Am J Ophthalmol 2000; 129:487-94

18. Hee MR, Puliafito Ca, Duker JS. Topography of diabetic macular edema with optical coherence tomography. Ophthalmology 1998; 105.360-370.

19.Trabucchi G, Brancato R, Pierro L. et al. Idiopathic juxtafoveolar retinal telengiectasis and pigment epithelial hyperplasia: an optical coherence tomographic study. Arch Ophthalmol 1999, 117:405-6.

20.Iijima H, Imai M, Gohdo T et al. Optical coherence tomography of idiopathic polypoidal choroidal

General Considerations

Examination of the fundus is increasingly important.Thesophisticatedmethodsavailable today provide great accuracy and significant information. Retinal exams may reveal the presence of vitreous and retinal diseases and even contribute to the detection of non-ocular diseases. Many systemic diseases can affect the anterior-posterior segments. Since the blood vessels of the retina are observed during the examination, certain systemic problems may be uncovered (e.g., high blood pressure or diabetes).

The need for frequency of eye exams generally differs with age and retinal diagnosis. A child with no symptoms should have an eye exam at age three. Early observation is important because permanent decrease in vision (e.g., amblyopia) can occur if not treated early, usually by ages 3-5. Some pa-

tients have moderate to high risk factors for eye disease (e.g., people with diabetes or a family history of eye disease) and may need more frequent checkups. Also, if older children have trouble in school, encounter problems with reading, or tend to rub their eyes when reading, a complete eye exam with retinal fundus observation may be necessary sooner. These observations are best accomplished after dilating the pupils and utilizing the indirect ophthalmoscope.

Completing the Evaluation with Additional Tests

In addition to direct and/or binocular indirect ophthalmoscopy, other techniques of examination may be indicated such as slitlamp indirect ophthalmoscopy (condensed lens), color tests, retinal fluorescein and indocyanine angiograms, ultrasonography, and OCT.

Observation of the Fundus

This observation includes but is not limited to the retina, blood vessels, and optic nerve. The optic nerve can be checked for swelling, neuritis, drusen or other problems. The blood vessels can be viewed for combined problems between retina and macula such as occlusions, hemorrhages, or neovascularization.1

Evaluation of the Central

Retina

In general, this evaluation is aimed to detect diabetic macular retinopathy, macular degeneration, and choroidal neovascularization (CNV) as well as other abnormalities of the retina, macula, optic nerve, and rare intraocular tumors. However, for cataract surgery candidates, preoperative evaluation of the macula is of particular relevance for establishing the cataract as the only cause of the patient’s poor vision.

Patient’s expectations for vision after cataract surgery are high, and the most common reason why patients do not see well after these procedures is macular dysfunction. Therefore, preoperative evaluation for pre-existing macular pathology is critical to allow detection of treatable disease or to inform patients that they may have a guarded visual prognosis (Figure 1).

Figure 1: Close-up Observation of the Macula. Careful biomicroscopic examination of the macula with the macula lens (inset) or the 3-4 mirror lens may reveal blood, macular thickening, an abnormal reflex or intraretinal spaces (edema) that may not be clearly detected by indirect ophthalmoscopy.

Choroidalneovascularizationlocatedunderneath the center of the fovea is the leading cause of legal blindness in the United States. Since the associated changes in the macula may be subtle, ophthalmologists should be cautious about overlooking them if the retina is examined quickly through a nondilated pupil.

Using video camera operating characteristics optimized for low light level imaging, non-mydriatic stereoscopic digital video retinal images provide substantial agreement with accepted “gold standard” ETDRS 35mm stereo fundus photography for retinal pathology diagnosis and excellent agreement for recommended retinal examination follow-up.2

Atpresent,dilatedindirectophthalmoscopy coupled with stereoscopic examination of the macula using slit lamp biomicroscopy remains the gold standard for rapid screening of the retina in the comprehensive ophthalmologist’s office.

Slit-Lamp Biomicroscopy and

Indirect Ophthalmoscopy

Using Condensing Lenses

During ophthalmoscopic exam with direct visualization (direct ophthalmoscope), small lesions or degenerations may be difficult to identify, especially because of their size, characteristics, and location.

With the help of small condensing (ie: 78 dp) lenses and the slit-lamp, the physician may obtain a real inverted and stereoscopic image with a wide field and an excellent resolution of the observed retina.

For this specialized observation different types of condensed lenses can be used, including the +90 dp, +78 dp, +60 dp, the super pupil lens (+135 dp), or the superfield lens. Although it is not necessary to dilate the

patient’s eye for this observation, the most recommended lens is the +90 dp or the super pupil lens (Figure 2).

Figure 2: Indirect Close-up Observation of the Posterior Pole. This revolutionary technique is a significant contribution to the anterior and posterior segment surgeon. With the 78 dp or 90 dp lens (inset) you may observe the posterior pole and macula in a general view without the need to dilate the patient´s pupil. With this kind of lenses, however, the ophthalmologist can not appreciate pathological alterations in detail as can be viewed with the lenses described in Figure 1.

Recommended Method

1). Low-to-moderate intensity of light is recommended, and the beam should be adjusted to a width between 3mm and 4 mm. The light beam will be perpendicular and with an inclination between the grades of 0 – 10.

2). Hold the lens at a distance of approximately 8 mm from the patient´s eye, almost touching the eyelashes. Once the retina is in focus, then the light beam intensity can be increased, or slit-lamp filters can be changed for a better contrast observation.

3). If the physician is interested in a specific area of the retina, the patient can be asked to follow the fixation target. The hand can be moved to look for the desired point.

4). The less lens potency in diopters, the greater the distance between the lens and the patient’s eye needed to observe the retina. For a comfortable distance and a good observation of the retina most times the +90 D lens is recommended.

The presence and depth of several alterations like subretinal fluid can be more effectively detected and evaluated using this method.

SCREENING METHODS

Non Mydriatic Digitized Video Retinal Imaging (NMDV)

The NMDV retinal images are taken in stereoscopic digital 35mm 30°, 7 standard-field retinal photographs. Stereo pairs are obtained from the posterior pole, nasal, superior, inferior, temporal, and the optic disc. Following pupil dilation, 35mm photography is performed. Using an appropriately validated digitalvideoimagingsystem,optimizedforlow light level imaging, and associated validated grading protocols, the NMDV system can be used to assess diabetic retinopathy, macular diseases, and other clinical conditions. This technology allows for follow-up by facilitating remote access of patients into an eye care program aimed at managing retinal eye disease.

Digital fundus photographs as well as the retinal angiogram pictures sequence have the advantage that they can be taken at minimal cost and inconvenience to the patient and can be transmitted by electronic mail through the Internet to distant experts, for consultation web or presentations.1