The appearance of the optic nerve head (the disc) and the nerve fiber layer is evaluated in the diagnosis and follow-up of glaucoma. The standard methods of detecting glaucoma include ophthalmoscopy, tonometry, perimetry, and gonioscopy. These procedures are considered part of the comprehensive ophthalmologic examination. Recently, other methods of measuring the optic disc and the nerve fiber layer have been developed in an attempt to create more accurate and reproducible methods of screening, detecting, and following structural parameters related to glaucoma. These methods include the following:
Confocal Laser Scanning Tomography
The confocal laser scanning tomographic ophthalmoscope is a device that scans layers of the retina to make quantitative measurements of the surface features of the optic nerve head and fundus. It has been used as an alternative to standard ophthalmologic methods of evaluating the optic nerve head and fundus in patients with glaucoma, papilledema, and other disorders affecting the retina. Other terms for confocal laser scanning tomography include: laser scanning topography, confocal scanning laser topography, electro-optic fundus imaging and scanning laser polarimetry. Types of confocal laser scanning ophthalmoscopes include:
Heidelberg Laser Tomographic Scanner or Heidelberg Retina Tomograph (HRT) (Heidelberg Engineering, Dossenheim, Germany),
TopSS Topographic Scanning System (Laser Diagnostic Technologies, San Diego, CA); and the
ZeissTM Confocal Laser Scanning Ophthalmoscope. (Zeiss Humphrey Systems, Dublin, CA).
Nerve Fiber Layer Testing or Analysis (Laser Scanning Polarimetry)
Thinning of the nerve fiber layer is associated with glaucomatous damage and has been shown to be correlated with visual field loss. The GDx Nerve Fiber Analysis System (Laser Diagnostic Technologies, Inc., San Diego, CA) is a confocal laser scanning ophthalmoscope with an integrated polarimeter. Instead of measuring topography, or height of the retina, like other confocal laser scanners, GDx measures the thickness of the retinal nerve fiber layer and then analyzes the results and compares them to a database of normative values.
The Retinal Thickness Analyzer (RTA) Digital Fundus Imaging (Talia Technology, Inc., Tampa, FL) uses a scanning laser biomicroscope that uses a laser to create a series of slit images of the retina that are digitalized and converted into a topographic map that quantifies retinal thickness.
Optical Coherence Tomography
Optical coherence tomography (OCT) (e.g., Humphrey OCT Scanner (Zeiss Humphrey, Dublin, CA)) has also been used for screening, diagnosis, and management of glaucoma and other retinal diseases. In OCT, low coherence near-infrared light is split into a probe and a reference beam. The probe beam is directed at the retina while the reference beam is sent to a moving reference mirror (AHFMR, 2003). The probe light beam is reflected from tissues according to their distance, thickness, and refractive index, and is then combined with the beam reflected from the moving reference mirror. When the path lengths of the two light beams coincide (known as constructive interference) this provides a measure of the depth and reflectivity of the tissue that is analogous to an ultrasound A scan at a single point. A computer then corrects for axial eye movement artifacts and constructs a two dimensional B mode image from successive longitudinal scans in the transverse direction. A map of the tissue is then generated based on the different reflective properties of its components, resulting in a real-time cross-sectional histological view of the tissue.
Barella et al (2013) examined the diagnostic accuracy of machine learning classifiers (MLCs) using RNFL and optic nerve (ON) parameters obtained with SD-OCT. A total of 57 patients with early-to-moderate POAG and 46 healthy patients were recruited. All 103 patients underwent a complete ophthalmological examination, achromatic standard automated perimetry, and imaging with SD-OCT. Receiver operating characteristic curves were built for RNFL and ON parameters. Ten MLCs were tested. Areas under ROC curves (aROCs) obtained for each SD-OCT parameter and MLC were compared. The mean age was 56.5 ± 8.9 years for healthy individuals and 59.9 ± 9.0 years for glaucoma patients (p = 0.054). Mean deviation values were -1.4 dB for healthy individuals and -4.0 dB for glaucoma patients (p < 0.001). Spectral domain-OCT parameters with the greatest aROCs were cup/disc area ratio (0.846) and average cup/disc (0.843). Areas under ROC curves obtained with classifiers varied from 0.687 (CTREE) to 0.877 (RAN). The aROC obtained with RAN (0.877) was not significantly different from the aROC obtained with the best single SD-OCT parameter (0.846) (p = 0.542). The authors concluded that MLCs showed good accuracy, but did not improve the sensitivity and specificity of SD-OCT for the diagnosis of glaucoma.
Bidot et al (2013) noted that OCT is used primarily in neuro-ophthalmology to measure thinning of the RNFL in optic neuropathies and to rule out a subtle maculopathy in patients complaining of blurred vision with a "normal" fundoscopic appearance. Only a few studies address the role of OCT in papilledema secondary to intra-cranial hypertension. Optical coherence tomography has been proposed as a diagnostic tool for mild papilledema, assisting the clinician in differentiating papilledema from optic nerve head drusen (ONHD), and for following the RNFL thickening from papilledema. However, the contribution of OCT in intra-cranial hypertension management is still unclear with the exception of its role in detecting associated maculopathy. Currently, OCT does not replace visual field testing and fundus examination.
In a comparative case-series study, Kulkarni et al (2014) evaluated the clinical utility of SD-OCT in differentiating mild papilledema from buried ONHD. A total of 16 eyes of 9 patients with ultrasound-proven buried ONHD, 12 eyes of 6 patients with less than or equal to Frisen grade 2 papilledema owing to idiopathic intra-cranial hypertension were included in this study. Two normal fellow eyes of patients with buried ONHD were included. A raster scan of the ON and analysis of the RNFL thickness was performed on each eye using SD-OCT. Eight eyes underwent enhanced depth imaging SD-OCT. Images were assessed qualitatively and quantitatively to identify differentiating features between buried ONHD and papilledema. Five clinicians trained with a tutorial and masked to the underlying diagnosis independently reviewed the SD-OCT images of each eye to determine the diagnosis. Main outcome measures were differences in RNFL thickness in each quadrant between the 2 groups and diagnostic accuracy of 5 independent clinicians based on the SD-OCT images alone. These investigators found no difference in RNFL thickness between buried ONHD and papilledema in any of the 4 quadrants. Diagnostic accuracy among the readers was low and ranged from 50 % to 64 %. The kappa coefficient of agreement among the readers was 0.35 (95 % confidence interval [CI]: 0.19 to 0.54). The authors concluded that SD-OCT is not clinically reliable in differentiating buried ONHD and mild papilledema.
Stereophotogrammetry, (Glaucoma-Scope (OIS, Sacramento, CA)) measures the dimensions of the optic disc in three-dimensional space using stereophotography. Stereophotographs are taken from two camera positions with parallel optical axes. Stereoanalysis of these photographs are used to determine the three-dimensional characteristics of the optic nerve head, and for following glaucomatous change of the optic nerve head over time. Stereoplotters and digital computer processing of scanned images have been used in an attempt to provide more quantitative, objective, and reproducible methods of measuring optic nerve disc changes.
Each of these methods has been used to image the optic nerve head in glaucoma patients. According to available guidelines, these methods may be used for documenting the appearance of the optic nerve head and retina in persons with glaucoma and other retinal diseases. But these devices have not been proven to be of value for screening of asymptomatic persons.
Available methods of optic nerve imaging (e.g., Heidelberg Retinal Tomograph, GDx confocal laser scanning polarimeter, Humphrey OCT Scanner, Glaucoma-Scope) were cleared by the U.S. Food and Drug Administration (FDA) based on a 510(k) premarket notification due to their “substantial equivalence” to other devices on the market. Thus, the manufacturers were not required to submit to the FDA the evidence that would be required to support a premarket approval application (PMA).
An American Academy of Ophthalmology (AAO)'s Preferred Practice Pattern on Primary Open Angle Glaucoma Suspect (2005) focuses on the management of persons with ocular hypertension or findings suggestive of ocular damage but without established glaucoma. The AAO guidelines define a glaucoma suspect as having one or more of the following characteristics: (i) visual fields suspicious for early glaucomatous damage; or (ii) intraocular pressure consistently above 21 mm Hg by applanation tonometry; or (iii) appearance of the optic disc or retinal nerve fiber layer that is suggestive of glaucomatous damage. Glaucomatous damage may be suggested by findings such as nerve fiber layer disc hemorrhage, asymmetric appearance of the optic disc or rim between fellow eyes that suggests loss of neural tissue, diffuse or focal narrowing or notching of the disc rim (especially at the inferior or superior poles), or diffuse or localized abnormalities of the retinal nerve fiber layer (especially at the inferior or superior poles). The AAO guidelines conclude that "[c]olor stereophotography or computer-based image analysis of the optic nerve head and retinal nerve fiber layer are the best currently available methods to document optic disc morphology and should be performed."
An AAO Preferred Practice Pattern on Primary Open-Angle Glaucoma (2005), which focuses on management of patients with evidence of glaucomatous damage as manifested by acquired optic nerve or nerve fiber layer abnormalities or typical visual field loss, states that optic nerve head and retinal nerve fiber layer analysis should be performed to document optic nerve head morphology.
Finnish evidence-based guidelines on open-angle glaucoma (Tuulonen et al, 2003) state: “High technology instruments (the Heidelberg retina tomograph, retinal nerve fibre analyser and optical coherence tomography), developed for nerve fibre layer and optic disc imaging and measurements, are not yet ready for routine glaucoma diagnostics. Due to their sensitivity and specificity, some instruments may be used for the follow-up of glaucoma.”
Aetna’s position on optic nerve and retinal imaging devices is based on the use of these devices as standard of care for documenting the appearance of the optic nerve head and retina, in place of retinal drawings or fundus photographs. In addition, optic nerve head imaging methods have been used as a noninvasive alternative to fluorescein angiography and slit-lamp biomicroscopy in assessing the retinal nerve fiber layer, although fluorescein angiography is also a sensitive test to detect leakage of incompetent retinal vessels. Because of the slow rate of progression of glaucoma, repeated optic nerve head imaging is not necessary more frequently than once every year.
Although optic nerve and retinal imaging devices have been used to document the appearance of the optic nerve head and retina, there is a lack of evidence from prospective clinical studies demonstrating that clinical outcomes are improved by incorporating this technology into glaucoma screening. A number of structured evidence reviews have concurred that there is limited evidence of the clinical utility of optic nerve head imaging methods in these situations (AHP, 1996; AHFMR, 1996; Lee, et al., 1996; TEC, 2001; AHFMR, 2003: TEC, 2003; IECS, 2003; AHFMR, 2006). A BlueCross BlueShield Association Technology Evaluation Center (2003) assessment of optic nerve imaging devices (termed retinal nerve fiber layer analysis (RNFLA) in the report) in the diagnosis and management of glaucoma and concluded that they do not meet TEC criteria. Using data from the Ocular Hypertension Treatment Study, the assessment found that RNFLA would not be useful in deciding whether to initiate early treatment of glaucoma or change treatment regimens, as the vast majority of patients with abnormal RNFLA test results would not be expected to go on to develop glaucoma. The assessment concluded: "The scientific evidence is insufficient to permit conclusions concerning the effects of RNFLA for the diagnosis or management of POAG [primary open angle glaucoma]; therefore, it is not possible to determine whether the procedure improves net health outcome."
The TEC assessment (BCBSA, 2003) focused on the best available evidence for retinal nerve fiber layer analysis. Although there are many published studies of retinal nerve fiber layer analysis (RNFLA), almost all of them are cross-sectional studies that evaluate the sensitivity and specificity of RNFA by comparing RNFA measurements of normal persons to persons with glaucoma or ocular hypertension. The assessment explains, however, that cross-sectional studies do not follow persons over time and are not designed to assess the relationship between a test result and subsequent development of disease. Studies that follow persons over time (longitudinal studies) are necessary to evaluate the ability of a test to predict which persons will develop disease and need treatment from those that will not develop disease.
Another limitation of published cross-sectional studies of RNFA is that they only compare normal persons to persons with glaucoma or ocular hypertension. Because these studies do not include persons with other ocular conditions, they do not provide information on the ability of RNFLA to distinguish patients with glaucoma or ocular hypertension from other ocular conditions. The subjects of these cross-sectional studies do not accurately reflect the spectrum of conditions that one would expect to see in the usual clinical practice setting (BCBSA, 2001). The external validity of these studies could be strengthened by selecting study subjects from a representative sample of the population of patients suspected of having the disease.
Cross-sectional studies cannot determine whether abnormalities that are detected by RNFA but not by any other standard method are early disease that might benefit from treatment (BCBSA, 2003). The most reliable evidence for assessing the clinical impact of RNFLA would be direct evidence from randomized trials comparing the impact on visual field defects of treatment initiated by different thresholds of RNFLA test results. As no such studies are available, technology assessments of RNFLA have had to rely on indirect evidence.
The most reliable indirect evidence to estimate diagnostic performance of RNFLA comes from longitudinal studies with a clinical population of patients suspected of having glaucoma, using follow-up for visual loss as a reference standard (BCBSA, 2003). The key issue in the early detection of glaucoma is how well test results predict the future development of visual loss. Thus, it is critical that the diagnostic performance of an early test be measured against follow-up for visual changes as the reference standard, in a longitudinal study.
The TEC assessment noted that no longitudinal study has yet appeared that selected subjects for whom RNFLA results are most likely to influence management decisions, that is, persons who have normal intraocular pressure and who do not meet conventional diagnostic criteria for glaucoma (BCBSA, 2003). The report identified only two published longitudinal studies that present data showing whether RNFLA changes precede development of visual field defects, on an individual patient basis. The most useful longitudinal evidence for the indication concerning detection of glaucoma comes from a subset of the Ocular Hypertension Treatment Study (Kamal et al, 2000). In this study, 21 patients progressed from ocular hypertension to glaucoma (converters) and 164 patients did not progress (nonconverters). Of the 21 converters, 13 had abnormal RNFLA results and in 11 of these the tests were positive prior to development of visual field defects (average lead time was 5.4 months). Of the 164 nonconverters, 47 had abnormal RNFLA results. Using this study’s results to estimate diagnostic performance, the positive predictive value of RNFLA, which is the most relevant index for early detection of glaucoma, is 22 % (13/60), so that 78 % of persons with signs of progression of glaucoma on RNFLA would not go on to develop visual field changes within the 6-year follow-up period of this study. The TEC assessment concluded that "a positive predictive value at this level does not appear to be sufficiently high for use in deciding to initiate early treatment or to change treatment regimens" (BCBSA, 2003). In addition, this study only included persons with ocular hypertension, and may not accurately reflect the performance of RNFLA in a cohort of glaucoma suspects without ocular hypertension. Given that the predictive values are dependent on the prevalence of the target condition in the population, the predictive value RNFLA in a population that includes individuals without ocular hypertension is likely to be even lower than the estimate from this study of ocular hypertensives, given that persons with ocular hypertension, an established glaucoma risk factor, are more likely to develop glaucoma than persons without ocular hypertension.
Chauhan et al (2001) reported on the results of a longitudinal study of RNFLA and visual field testing (perimetry) in patients with glaucoma who were followed for a median of 5.5 years. In 29 percent of cases, progression was detected by both perimetry and RNFLA; when progression was detected by both tests, it was just as common for perimetry to detect it first as it is for RNFLA to detect it first. Although progression was observed by RNFLA alone in 40 % of patients, it is unclear from this study how often such patients experience visual progression (true positives versus false positives). The TEC assessment (2003) emphasizes that the key issue in the early detection of glaucoma is how well test results predict the future development of visual loss, as loss of vision is an endpoint that patients experience in terms of quality of life and ability to function.
A report on glaucoma screening prepared for the UK National Screening Committee (Spry and Sparrow, 2003) stated that methods of assessing optic nerve head appearance using images acquired by digital scanning laser instrumentation are quantitative and rapid to perform. The report concluded, however, that “[t]o date, however, scant longitudinal information is available on individuals who exhibit apparent structural abnormalities with these techniques but no glaucomatous loss of visual function.” The ability to utilize optic nerve head appearance in assessing glaucoma risk is limited by the fact that “considerable overlap exists between the distribution of relevant parameters found in patients with glaucoma and normal individuals.”
The AAO and the American Glaucoma Society prepared a work group report to provide a “rationale for [insurance] coverage” of optic nerve head imaging (Remey 2002; AAO, 2003; AAO/AGS, 2003). The AAO/AGS Work Group statement (2003) on the clinical utility of optic nerve scanning devices in screening focused exclusively on comparisons with automated perimetry or photography used alone. However, the standard methods of detecting and monitoring glaucoma include ophthalmoscopy (to inspect the optic disk and nerve fiber layer), drawings of the optic nerve head and stereoscopic disc photographs (to document the status of the optic nerve head), tonometry (to measure intraocular pressure), perimetry (to measure visual fields), and gonioscopy (to measure the angle of the anterior chamber).
None of the studies cited in the AAO/AGS Work Group statement (2003) represented prospective clinical outcome studies. The need for prospective clinical outcome studies comparing optic nerve scanning devices to standard methods of evaluation is especially critical given that there is no established gold standard comparison test for predicting the risk of glaucoma development prior to the onset of visual field defects. Although RNFLA devices have been in commercial use for more than a decade, the quality of evidence supporting their use remains limited, and the best available evidence indicates that the ability of RNFLA to predict progression to glaucoma is limited.
The monograph from the AAO/AGS Work Group (2003) commented on the limited quality of evidence supporting the use of optic nerve scanning devices. The monograph stated: "In clinical practice, many patients now are tested with more advanced visual field techniques designed to detect glaucoma earlier. Yet these variations on visual field testing have not required rigorous TEC assessment to determine if they are useful. Clinical experience, cross-sectional studies, and a few longitudinal cohort studies have shown that they are useful improvements in our ability to detect glaucoma and/or progression. The case is similar to RNFLA, where clinicians and researchers have determined that this newer technology surpasses or equals the current clinical assessment of the optic nerve and nerve fiber layer."
Assessment of the evidence supporting the use of optic nerve scanning devices is required because these techniques have been presented as a new technology rather than as an incremental advance over an existing technology such as ophthalmoscopy or other established methods of evaluating the retina and optic nerve head.
The Center for Medicare and Medicaid Services (CMS) has not established a national coverage position on optic nerve imaging devices; CMS has left coverage of optic nerve imaging devices to the discretion of local Medicare carriers.
Optical coherence tomography (OCT) (e.g., Humphrey OCT Scanner (Zeiss Humphrey Systems, Dublin, CA) has also been used for screening, diagnosis, and management of glaucoma and other retinal diseases. Optical coherence tomography (OCT) is a relatively new non-invasive imaging modality that uses reflected light in a manner analogous to the use of sound waves in ultrasonography to create high-resolution (10 micron) cross-sectional images of the vitreoretinal interface, retina and subretinal space, analogous to histological sections seen through a light microscope. OCT also gives quantitative information about the peripapillary retinal nerve fiber layer thickness.
The Alberta Heritage Foundation for Medical Research (2003) assessed the value of optical coherence tomography (OCT) in the diagnosis of retinal diseases. It stated that “OCT appears promising for diagnosing patients with cystoid macular edema and moderate glaucoma.”
OCT can determine the presence of cystoid macular edema (CME) by visualizing the fluid-filled spaces in the retina. The amount of CME can be monitored over time by quantifying the area of cystoid spaces on a cross-sectional image through the macula. Studies have reported OCT to be comparable to fluorescein angiography in the evaluation of CME. However, fluorescein angiography may be a more sensitive study for leakage of incompetent retinal vessels (Roth, 2001).
OCT, scanning laser ophthalmoscope, and confocal laser tomography may also be useful in macular holes, in establishing the status of the vitreomacular interface and distinguishing full-thickness holes from lamellar holes and macular cystic lesions (Valero and Atebara, 2001). According to the American Academy of Ophthalmology (2003), “[i]n most cases the diagnosis [of macular hole] is made by clinical evaluation. Optical coherence tomography provides information on the anatomy of the macular hole and may aid in the diagnosis and staging.”
OCT has also been used in a variety of other retinal diseases. In diabetic retinopathy, OCT has been used to evaluate retinal swelling and serous retinal detachment. OCT has been able to demonstrate a moderate correlation between retinal thickness and best-corrected visual acuity, and it has been able to demonstrate three basic structural changes of the retina from diabetic retinal edema, i.e., retinal swelling, cystoid edema, and serous retinal detachment (Khan and Lam, 2004). There is, however, a lack of prospective clinical studies demonstrating that clinical outcomes are improved by incorporating OCT into screening of persons with diabetes for retinopathy. Current guidelines from the American Diabetes Association do not incorporate OCT into diabetic retinopathy screening algorithms. Optical coherence tomography can be useful for quantifying retinal thickness, monitoring partial resolution of macular edema, and identifying vitreomacular traction in selected patients with diabetic macular edema caused by a taut posterior hyaloid face (AAO, 2003). The AAO (2003) states that this test might be considered in diabetic retinopathy patients unresponsive to laser treatment for macular edema for whom the ophthalmologist is considering vitrectomy with removal of the posterior hyaloid face.
OCT has also been used to determine the presence of subretinal fluid and in documenting the degree of retinal thickening in age-related macular degeneration (AMD). This study has shown decreased reflectance at the level of the rod-cone layer indicating that atrophy is present in this layer (Maturi, 2005). According to guidelines from the AAO (2003), “the value of this test in evaluating and treating AMD remains unknown.”
OCT is also being investigated in evaluating choroidal neovascularization (CNV). Well-defined and diffuse CNV have characteristic appearances on OCT, as do subretinal hemorrhages and retinal detachments. Despite the many advantages of OCT, fluorescein angiography remains the imaging modality of choice in the management of CNV. Currently, OCT cannot replace fluorescein angiography in the management of CNV (Wu, 2005).
Alberta Heritage Foundation for Medical Research (2003) stated that “while OCT appears promising for diagnosing patients with cystoid macular edema and moderate glaucoma, it still has a number of practical and theoretical limitations. Its ability to detect any other of the myriad retinal diseases is unknown. It is clear that OCT in its current state of development is ineffective as a stand alone diagnostic test, but a study has not yet been conducted to assess its value as part of a serial testing strategy. The position of OCT in the scheme of testing needs to be established so that an optimal testing strategy can be identified that is both highly accurate and clinically practical. Randomized controlled trials are also needed to establish the clinical impact of OCT diagnostic imaging on the management, treatment options, and outcomes of patients”. The AHFMR reasoned that “[w]hile OCT appears promising as a tool for diagnosing retinal disease, there are many questions relating to its clinical utility that are not likely to be answered by a cross-sectional study. Longitudinal studies are needed to determine the temporal relationship between OCT RNFL thickness measurements and visual field defects, and to identify any changes in RNFL thickness that could predict future visual deterioration.”
A more recent assessment by the Alberta Heritage Foundation for Medical Reseach (AHFMR, 2006) summarized the current status of ophthalmic scanning devices in glaucoma. The assessment concluded: "B ased on results from three systematic reviews, the value of CSLO [confocal scanning laser ophthalmoscopy] and SLP [scanning laser polarimetry] as diagnostic tools for the detection of early glaucoma remains unclear, although the HRT and GDx methods hold considerable promise for the detection of glaucoma-associated structural change. The available evidence showed that HRT and GDx are able to differentiate between normal individuals and those with glaucoma. However, whether these devices have the sensitivity and specificity to detect the early onset of glaucoma, before the onset of visual field loss, remains to be determined. The available CSLO and SLP devicesstill await prospective validation against accepted measures of structural and functional change in terms of whether the use of a test results improves patient outcomes and is helpful in patient management and obviates unnecessary treatment."
The United Kingdom National Health Service National Coordinating Centre for Healthcare Technology Assessment (NCCHTA) conducted primary research and a comprehensive systemic review of the ophthalmic scanning devices in glaucoma screening (Kwartz et al, 2005). The assessment concluded "[t]he findings of the glaucoma imaging study suggest that, although optic nerve head tomography and scanning laser polarimetry provide good-quality digital images, their data may contribute little to a patient's clinical diagnosis but would add significantly to the cost of their assessment."
Hickman (2007) reviewed the last 10 years of progress in the imaging of the optic nerve with a particular focus on applications to multiple sclerosis (MS). Development of magnetic resonance imaging (MRI) of the optic nerve has lagged behind imaging of other parts of the CNS. These limitations are due to technical challenges related to the small size and mobility of the optic nerves and artefacts caused by surrounding cerebrospinal fluid, orbital fat, and air-bone interfaces. Nonetheless, the last 10 years has seen significant progress with regard to detecting optic nerve atrophy following optic neuritis, the use of fat- and CSF-suppressed high resolution imaging, the ability to measure magnetization transfer ratio and diffusivity in the optic nerve, and the emergence of SPIR-FLAIR for increasing sensitivity to inflammatory demyelination. Remaining challenges include further reduction of movement artifacts, testing ultra-high field MRI systems and dedicated surface coils, and developing automated segmentation techniques to improve the reproducibility of quantitative measurements. Finally the role of OCT as a marker of retinal damage needs to be clarified further through correlations with MRI, clinical, and electrophysiologic data.
In a report on optic nerve head and retinal nerve fiber layer analysis by the American Academy of Ophthalmology, Lin and associates (2007) evaluated the current published literature on the use of optic nerve head (ONH) and retinal nerve fiber layer (RNFL) measurement devices in diagnosing open-angle glaucoma and detecting progression. The authors concluded that ONH and RNFL imaging devices provide quantitative information for the clinician. Based on studies that have compared the various available technologies directly, there is no single imaging device that outperforms the others in distinguishing patients with glaucoma from controls.
In a report on laser scanning imaging for macular disease by the American Academy of Ophthalmology, McDonald and colleagues (2007) examined if laser scanning imaging is a sensitive and specific tool for detecting macular disease when compared with the current standard technique of slit-lamp biomicroscopy or stereoscopic fundus photography. Literature searches conducted in December 2004 and in August 2006 retrieved 370 citations. The Retina Panel members selected 65 articles for the panel methodologist to review and rate according to the strength of the evidence. Of the 65 articles reviewed, 6 provided level I evidence, 9 provided level II evidence, and 50 provided level III evidence. A level I rating was assigned to studies that reported an independent masked comparison of an appropriate spectrum of consecutive patients, all of whom had undergone both the diagnostic test and the reference standard. A level II rating was assigned to an independent masked or objective comparison; a study performed in a set of non-consecutive patients or confined to a narrow spectrum of study individuals (or both), all of whom had undergone both the diagnostic test and the reference standard; or an independent masked comparison of an appropriate spectrum, but the reference standard had not been applied to all study patients. A level III rating was assigned when the reference standard was unobjective, unmasked, or not independent; positive and negative tests were verified using separate reference standards; or the study was performed in an inappropriate spectrum of patients. There are high-level studies of the use of laser scanning imaging to quantify macular thickness and, thereby, macular edema in patients with diabetic retinopathy and to examine patients with a macular hole. There is lower-quality evidence on the use of laser scanning imaging for other diseases of the macula. There is insufficient evidence to compare the different instruments. The authors concluded that there is level I evidence that laser scanning imaging can accurately and reliably quantify macular thickness in patients with diabetic retinopathy. There is level I evidence that OCT provides additional information to clinical examination when used in patients with a macular hole. Laser scanning imaging provides important information that is helpful in patient management by allowing objective serial quantitative measurements. Although further studies are needed to develop an optimal testing strategy using these imaging modalities, laser scanning imaging is a sensitive, specific, reproducible tool for diagnosing macular edema and, therefore, is likely to be useful for managing diseases that result in macular edema.
In a prospective, controlled, single-center study, Ibrahim and colleagues (2010) examined the applicability of tear meniscus height (TMH) measurement using Visante OCT in the diagnosis of dry eye disease. A total of 24 right eyes of 24 patients (6 males, 18 females; mean age of 63.14 +/- 13.4 years) with definite dry eye according to the Japanese dry eye diagnostic criteria and 27 right eyes of 27 control subjects (12 males, 15 females; mean age of 56.04 +/- 14.22 years) were recruited. All subjects underwent slit-lamp TMH measurement, OCT upper and lower TMH measurements, tear film breakup time (BUT) measurements, vital stainings, and Schirmer test. The results were compared between the 2 groups by Mann-Whitney test. Main outcome measures were the correlation between the clinical findings of slit-lamp TMH, strip meniscometry examination, tear functions, vital staining scores, and the OCT upper and lower TMH parameters were tested by Spearman's correlation test. Receiver operating characteristic (ROC) curve technique was used to evaluate the sensitivity, specificity and cut-off values of OCT TMH examination in the diagnosis of dry eye. The OCT upper and lower TMH values, slit-lamp TMH, strip meniscometry, tear film BUT, and vital staining scores were significantly lower in the dry eye patients compared with controls (p < 0.001). A significant correlation between the OCT upper and lower TMH measurements as well as slit-lamp TMH, strip meniscometry, tear functions, vital staining scores, and the Schirmer test was found. The ROC curve technique analysis of the OCT lower TMH showed that, when the cut-off value was set at less than 0.30 mm, the sensitivity and specificity of the testing were 67 % and 81 %, respectively. The authors concluded that Visante OCT is a quick, non-invasive method for assessing the TMH, with acceptable sensitivity, specificity, and repeatability, and may have potential applications for the diagnosis and evaluation of dry eye disease. They also stated that further studies on OCT TMH should determine age- and gender-specific cut-off values, sensitivity, specificity of the test in the diagnosis of dry eye disease when performed alone or in conjunction with other dry eye tests.
In a prospective, cross-sectional study, Jeoung et al (2010) evaluated quantitatively the degree of diffuse retinal nerve fiber layer (RNFL) atrophy using Stratus optical OCT. A total of 102 eyes of 102 patients with diffuse RNFL atrophy and 102 healthy eyes of 102 age-matched subjects were enrolled in the Diffuse Atrophy Imaging Study. Two experienced observers graded RNFL photographs of diffuse RNFL atrophy eyes using a previously reported standardized protocol with a 4-level grading system. Readings were taken from the superior and inferior RNFL areas. The OCT-measured RNFL thickness parameters were compared among normal eyes and diffuse atrophy subgroups. Area under the ROCs (AROCs) was calculated for various OCT RNFL parameters. Main outcome measures were average and segmental (4 quadrants and 12 clock-hours) OCT-measured RNFL thicknesses and AROCs for various OCT parameters. For superior and inferior RNFL areas, diffuse atrophy grading by 2 observers agreed in 82.5 % and 83.3 % of cases, respectively, with a substantial agreement (kappa value = 0.760 [p < 0.001] and 0.777 [p < 0.001]). Significant differences were observed in RNFL thickness among normal and all diffuse atrophy subgroups, especially in the 7 and 11 o'clock sectors (p < 0.0001). The OCT RNFL thickness measurements decreased with increasing severity of RNFL damage. The 7 and 11 o'clock sectors showed the highest AROCs for discrimination of mild RNFL atrophy from normal eyes (0.972 and 0.979, respectively). The authors concluded that the OCT RNFL thickness parameters showed excellent quantitative correlation with the degree of diffuse RNFL atrophy. These findings suggested that Stratus OCT may serve as a useful adjunct in accurately and objectively assessing the degree of diffuse RNFL atrophy. Moreover, the authors noted that further studies are needed to assess the diagnostic ability of the Stratus OCT with its internal normative database to detect diffuse RNFL atrophy.
Cettomai and associates (2010) performed clinical and OCT examinations on 240 patients attending a neurology clinic. Using OCT 5th percentile to define abnormal RNFL thickness, these investigators compared eyes classified by neurologists as having optic atrophy to RNFL thickness, and afferent pupillary defect (APD) to RNFL thickness ratios of eye pairs. Mean RNFL thickness was less in eyes classified by neurologists as having optic atrophy (79.4 +/- 21 μm; n = 63) versus those without (97.0 +/- 15 μm; n = 417; p < 0.001, t-test) and in eyes with an APD (84.1 +/- 16 μm; n = 44) than without an APD (95.8 +/- 17 μm; n = 436; p < 0.001). Physicians' diagnostic accuracy for detecting pallor in eyes with an abnormal RNFL thickness was 79 % (sensitivity = 0.56; specificity = 0.82). Accuracy for detecting a retinal APD in patients with mean RNFL ratio (affected eye to unaffected eye) less than 0.90 was 73 % (sensitivity = 0.30; specificity = 0.86). Ability to detect visual pathway injury via assessment of atrophy and APD differed between neurologists. The authors concluded that OCT reveals RNFL abnormality in many patients in whom eyes are not classified by neurologic examiners as having optic atrophy. They stated that further study is needed to define the role of OCT measures in the context of examinations for optic atrophy and APD by neuroophthalmologists.
In a retrospective chart review, Ota et al (2010) studied morphologic changes of serous retinal detachment (SRD) and hyper-reflective dots, which have been reported to be precursors of hard exudates, detectable in SRD using OCT to assess whether or not the OCT findings are correlated with the subfoveal deposition of hard exudates in patients with diabetic macular edema (DME) accompanied by SRD. A total of 28 eyes of 19 patients with DME accompanied by SRD were included in this analysis. These researchers imaged SRD and the hyper-reflective dots in SRD using spectral domain OCT (SD-OCT). The number and distribution of the hyper-reflective dots in SRD were evaluated before the initial treatment at the authors' hospital for DME accompanied by SRD. Based on a difference in the SD-OCT findings, the study eyes were divided into 2 groups: (i) eyes with a few dots and (ii) those with many dots. These investigators studied the clinical course of these 2 groups to assess whether or not the findings of SRD and hyper-reflective dots on the SD-OCT images were correlated with deposition of hard exudates in the subfoveal space during follow-up. Main outcome measures were correlation of the SD-OCT findings of SRD and hyper-reflective dots with deposition of hard exudates in the subfovea of patients with DME accompanied by SRD. Subfoveal deposition of hard exudates was seen in 11 of the 28 eyes at the final examination. Before initial treatment at the authors' hospital, 14 eyes had a few hyper-reflective dots SRD and 14 eyes had many hyper-reflective dots. Whereas no deposition of hard exudates in the subfoveal space was seen in the former eyes, it was seen in 11 of the latter 14 eyes (p < 0.0001). In addition, using SD-OCT, these researchers found discontinuity of the outer border of detached neurosensory retina in 9 of the 28 eyes. Of these 9 eyes, 1 was in the group with few hyper-reflective dots and 8 were in the group with many hyperreflective dots (p = 0.0046). The authors concldued that in patients with DME accompanied by SRD, SD-OCT revealed that hyper-reflective dots may be associated with the subfoveal deposition of hard exudates during follow-up. Furthermore, they noted that further prospective studies with a larger sample size are needed to elucidate these details of SRDand the reason(s) why foveal deposition of hard exudates occurs in eyes with DME.
Marmor et al (2011) stated that the AAO recommendations for screening of chloroquine (CQ) and hydroxychloroquine (HCQ) retinopathy were published in 2002, but improved screening tools and new knowledge about the prevalence of toxicity have appeared in the ensuing years. No treatment exists as yet for this disorder, so it is imperative that patients and their physicians be aware of the best practices for minimizing toxic damage. New data have shown that the risk of toxicity increases sharply toward 1 % after 5 to 7 years of use, or a cumulative dose of 1000 g of HCQ. The risk increases further with continued use of the drug. The prior recommendation emphasized dosing by weight. However, most patients are routinely given 400 mg of HCQ daily (or 250 mg CQ). This dose is now considered acceptable, except for individuals of short stature, for whom the dose should be determined on the basis of ideal body weight to avoid overdosage. A baseline examination is advised for patients starting these drugs to serve as a reference point and to rule out maculopathy, which might be a contraindication to their use. Annual screening should begin after 5 years (or sooner if there are unusual risk factors). Newer objective tests, such as multi-focal electro-retinogram (mfERG), spectral domain-OCT(SD-OCT), and fundus auto-fluorescence (FAF), can be more sensitive than visual fields. It is now recommended that along with 10-2 automated fields, at least one of these procedures be used for routine screening where available. When fields are performed independently, even the most subtle 10-2 field changes should be taken seriously and are an indication for evaluation by objective testing. Because mfERG testing is an objective test that evaluates function, it may be used in place of visual fields. Amsler grid testing is no longer recommended. Fundus examinations are advised for documentation, but visible bull's-eye maculopathy is a late change, and the goal of screening is to recognize toxicity at an earlier stage. Patients should be aware of the risk of toxicity and the rationale for screening (to detect early changes and minimize visual loss, not necessarily to prevent it). The drugs should be stopped if possible when toxicity is recognized or strongly suspected, but this is a decision to be made in conjunction with patients and their medical physicians.