All subjects underwent a complete ophthalmologic examination, including a medical and family history, best-corrected visual acuity testing with Early Treatment Diabetic Retinopathy Study charts, Humphrey SITA standard 24-2 visual field testing, applanation tonometry, slitlamp biomicroscopy, indirect ophthalmoscopy, and color fundus photography. Healthy subjects were examined at New England Eye Center between August 1, 2003, and February 27, 2004. All participants engaged in an informed consent process and signed a written consent document before study procedures were carried out. The study protocol was approved and monitored by the Human Investigation Review Committee at New England Medical Center. To our knowledge, this is the first study to provide normative macular thickness data for the OCT3 system. This study measures and defines normal macular thickness values in healthy eyes using OCT3 mapping software. Therefore, as the OCT3 becomes more widely available and used, normative data will be important in interpreting pathological features of the macula. The measurements from the 2 instruments were statistically different. Scans were acquired from both eyes of 8 consecutive patients with suspected macular edema. Recently, Frank et al 23 compared macular thickness measurements from 2 versions of OCT scanners: OCT1 and OCT3. Based on our experience with the OCT3 and previous versions of the system, we observe that the macular thickness measurements for healthy eyes are higher than the values obtained using earlier versions of the instrument, including the prototype OCT. It provides a 4-fold increase in imaging speed and better resolution (axial resolution, <10 μm) than earlier generations of the instrument. The latest OCT model (Stratus OCT Carl Zeiss Meditec, Dublin, Calif) was made commercially available in 2002.
4 The introduction of optical coherence tomography (OCT) has enabled clinicians to reliably detect and measure small changes in macular thickness and to quantitatively evaluate the efficacy of different therapeutic modalities. Traditional methods for evaluating macular edema, such as slitlamp biomicroscopy, stereoscopic photography, and fluorescein angiography, are relatively insensitive to small changes in retinal thickness and are qualitative at best. 1, 2 Nussenblatt et al 3 were able to demonstrate that the degree of macular thickening, rather than the presence of macular edema, is significantly correlated with visual acuity. However, it has been observed repeatedly in clinical practice that the presence of macular edema does not necessarily preclude good vision. This process can be found in those with diabetic retinopathy, retinal vein occlusion, uveitis, and other ocular disorders.
Abnormal fluid accumulation within the retina and a concomitant increase in retinal thickness usually result from the breakdown of the blood-retinal barrier. Macular edema is a common cause of visual loss.
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