Study On The Changes Of Photoreceptor IS/OS Junctions Before And After Surgery In Idiopathic Macular Hole By Spectral Domain Optical Coherence Tomography

BackgroundIn the past more than10years,a new technique of medical tomography named optical coherence tomography was brought into the world followed after X-ray,CT,MRI and ultrasound. It encompassed the semiconductor laser technology, optical technology and computer image processing technique and developed at high speeds. OCT had emerged as an effective noninvasive method for examining the retinal architecture and for the management of macular abnormalities, including idiopathic macular holes (IMHs). In ophthalmology, OCT provided so far the best technology imaging the retinal ultrastructure including the layer of ganglion cells,photoreceptor IS/OS junctions, external limiting membrane(ELM) and RPEs. So OCT images offered a better help to describe how macular holes formed and to explain the causes of vision loss and to give a good postoperative visual acuity evaluation than other traditional checks. With the improvement of surgical techniques and equipments, the macular hole closure rate in IMH patients increased. However, in postoperative IMH patients with closed macular holes confirmed by OCT the VA recovery varied in different degrees,some even declined. And this made people look for kinds of parameters to evaluate the VA recovery in IMH. The past TD-OCT mainly concentrated in macular hole diameter,basal hole diameter, hole area, foveal retinal thickness, hole patterns, edema degrees of nasal and temporal edge of macular hole. Some scholars found that the size of macular hole and the thickness of neural fiber layer on the margin of the hole were closely linked with the VA in retrospective studies. But some other scholars found no correlations between hole area,basal hole diameter,hole location and VA in lamellar macular holes.And they also found the conclusion of "the bigger the hole,the worse the VA"was not always right.Therefore,to search for a better parameter to evaluate the VA recovery in IMH patients by SD-OCT became a focus of researchers.As the photoreceptor IS/OS junction is an important creature of light information into electrical signals to the central nervous system, the integrity of IS/OS was considered to to be a symbol of good photoreceptors and the key indicator of prognosis assessment of VA in patients with idiopathic macular hole. More and more studies showed that the changes of IS/OS associated with VA in IMH patients by SD-OCT. Some researchers divided IS/OS junctions into different forms of continuous, broken and missing in a qualitative analysis. Some researchers had even measured the horizontal and vertical diameters of IS/OS absence(DIOA) and then calculate the hole area by multiplication. To study the correlation between DIOA and logMAR before and after surgery in idiopathic macular hole(IMH) by spectral domain optical coherence tomography is our aim of the prospective research.The "idiopathic" means that the cause of a disease is still not clear. And the pathogenesis of IMH has been one of the focuses in ophthalmologists for many years. Now it is recognized that the tangential traction of vitreous on macular foveal is a major cause of IMH from Gass’ Theory. Through extensive observation and later coming OCT technology to track patients with vitreomacular traction syndrome(VMTS), some scholars found more than50%eventually developed into a full thickness macular hole. The other researchers discovered that the posterior vitreous detachment(PVD) forword against foveal traction combined with the rotation of the eyeball was the beginning cause of the disease by SD-OCT. All above were concluded from the vitreoretinal interface considerations. But still some other scholars had operated artificial posterior vitreous detachment in the full thickness IMH eyes failed to get OCT images in order to find if the vitreous was still sticking to the posterior retina. And the results showed that in the case of full thickness holes had formed, there were still some eyes without posterior vitreous detachment. This proved that the tangential traction caused by PVD maybe not the only factor. More recently, scholars at home and abroad found the SFCT decreased with increasing age in normal population and the female thinner than the male at the same age. So the eyesight of scholars was focused on the choroidal thickness for IMH happened in older female at a large proportion.But imaging the choroid with conventional commercial spectral-domain optical coherence tomography (SD-OCT) has been difficult, mainly because of difficulty in signal transmission beyond the retinal pigment epithelium. A recent modification to the standard technique, termed enhanced depth imaging optical coherence to-mography (EDI-OCT), was able to image the choroid with reasonable clarity using commercial SD-OCTs. The choroid, which accounts for most ocular blood flow, may be affected in several disease states, such as polypoidal choroidal vasculopathy and choroidal melanoma. It is also prone to suffer from age-related degeneration, microvascular artherosclerotic changes, and changes inherent to other microvascular systems.An understanding of the choroid using non-invasive imaging techniques has been limited. For instance, imaging of the choroid with OCT was not entirely possible.This was because the wavelength of the light source used to image the retina was not long enough to penetrate into the choroid.This was due to wavelength dependent light scattering and signal loss that occur in the image path, decreased sensitivity away from zero-delay, and the various inherited limitations with Fourier transformation.The common commercially available OCTs employ a wavelength of800nm, whereas those capable of choroidal imaging are in the range of1,060nm. One would have to use a light source nearer to the infrared region to penetrate into the choroid. This was not possible for most commercially available OCTs, because clarity for retinal structures would be compromised. To conclusion,the reasons why the choroid cannot be imaged clearly could be attributed to (1) decreasing sensitivity and resolution with increasing displacement from zero-delay,(2) decreased maximal dynamic range inherent in Fourier domain systems,(3) wavelength dependent light scattering and signal loss in the image path, and (4) the lateral width of the defocused imaging beam. When the instrument is moved closer to the eye to image deeper layers, the inverted image is displayed such that the choroid is shown facing up (ie, closer to zero-delay) while the inner retina is facing down. This has the effect of delivering the most closely focused portion of the illumination at the level of the choroid or the inner scleral border. Hence, the choroid can be imaged at higher sensitivity.Following the introduction of a new imaging technique, referred to as "enhanced depth imaging optical coherence tomography"(EDI-OCT), choroidal imaging with standard commercially available spectral-domain OCT (SD-OCT) was made possible.At the same time, retinal details could be seen with comparable quality.Part1. Observation of photoreceptor IS/OS junctions before and after surgery in idiopathic macular hole using spectral domain optical coherence tomographyObjective To evaluate photoreceptor inner segment/outer segment(IS/OS) junctions before and after surgery in idiopathic macular hole(IMH) using spectral domain optical coherence tomography(SD-OCT).Methods Prospective study of23patients(25eyes) who underwent macular hole surgery. Date collection included pre-and postoperative diameters of IS/OS absence(DIOA) in horizontal direction by SD-OCT(Topcon CO.Version3.21). The differences of pre-and postoperative diameters of IS/OS absence(DIOA) were analyzed with Paired-Samples T Test and the correlations were tested with Bivariate-Pearson Correlation.Results Macular holes in18eyes had successful anatomic closure and the closure rate was72%. The preoperative DIOA distributed from551μm to2900μm and the mean preoperative DIOA was1933.16±650.80μm. The postoperative DIOA distributed from412μm to2811μm and the mean postoperative DIOA was1329.20±780.3μm. Compared with the preoperative DIOA, the postoperative DIOA almost decreased604μm12months later and the differences had statistical significance by Paired-Samples T Test (t=3.73,P=0.001). Pre-and postoperative DIOA had no correlations by Bivariate-Pearson Correlation(r=0.37,P=0.069).Conclusions SD-OCT can be valuable for the observation of IS/OS junctions in patients with idiopathic macular hole. The postoperative DIOA was smaller than the preoperative significantly but without statistical correlations between them. Part2. Correction study of visual acuity and photoreceptor IS/OS junction in idiopathic macular hole by spectral domain optical coherence tomographyObjective To study the correlation between photoreceptor inner segment/outer segment(IS/OS) junction and visual acuity (VA) before and after surgery in idiopathic macular hole(IMH) on spectral domain optical coherence tomography(SD-OCT). Methods Prospective study of charts of28patients(30eyes) who underwent macular hole surgery. Date collection included pre-and postoperative best-corrected visual acuity(BCVA) which was converted to logMAR score, and diameters of IS/OS absence(DIOA) in horizontal direction. The above data was analyzed by Paired-Samples T Test and Bivariate-Pearson correlation.Results Macular holes in22eyes had successful anatomic closure and the closure rate was73.3%. The preoperative logMAR distributed from0.18to1.30and the mean preoperative logMAR was0.99±0.37. The postoperative logMAR distributed from0.10to1.60, and the mean postoperative logMAR was10.75±0.46. Compared with the preoperative logMAR, the postoperative logMAR decreased0.24and the differences had statistical significance by Paired-Samples T Test (t=2.859,P=0.008).The preoperative DIOA distributed from551μm to2900μm and the mean preoperative DIOA was1945.57±609.33μm. The postoperative DIOA distributed from412μm to2811μm and the mean postoperative DIOA12months later was1357.07±772.67μm. Compared with the preoperative DIOA, the postoperative almost decreased589μm and the differences had statistical significance by Paired-Samples T Test (t=3.94,P<0.001). Preoperative logMAR and DIOA were positive correlated significantly by Bivariate-Pearson Correlation(r=0.895,P<0.01). Also the postoperative logMAR and DIOA were positive correlated significantly by Bivariate-Pearson Correlation(r=0.921,P<0.01).Conclusions The postoperative visual ability and DIOA improved clearly. Preoperative and postoperative logMAR and DIOA were positive correlated significantly and DIOA maybe an important indicator of visual recovery in patients with idiopathic macular hole. Part3. Correction study of photoreceptor IS/OS junction and subfoveal choroidal thickness in idiopathic macular hole by spectral domain optical coherence tomographyObjective To observe the correlation between photoreceptor inner segment/outer segment(IS/OS) junction and subfoveal choroidal thickness(SFCT) before and after surgery in idiopathic macular hole(IMH) by enhanced depth imaging(EDI) of spectral domain optical coherence tomography(SD-OCT).Methods35unilateral IMH patients who underwent macular hole surgery were studed,including8males and27females. Pre-and postoperative diameters of IS/OS absence(DIOA) and SFCT in horizontal direction were determined by EDI-OCT. The above data was analyzed by Paired-Samples T Test and Bivariate-Pearson correlation.Results29eyes were anatomically closed and the closure rate was83%. The preoperative DIOA distributed from386μm to2900μm and the mean preoperative DIOA was1257.49±678.39μm. The postoperative DIOA6months later distributed from203μm to1410μm and the mean postoperative DIOA was660.80±298.59μm. Compared with the preoperative DIOA, the postoperative almost decreased597μm and the differences had statistical significance by Paired-Samples T Test it=6.926,P<0.001). The preoperative SFCT distributed from85μm to268μm and the mean preoperative SFCT was130.80±37.09μm. The postoperative SFCT6months later distributed from93μm to201μm, and the mean postoperative SFCT was137.17±32.64μm. Compared with the preoperative SFCT, the postoperative SFCT increased about6.37μm and the differences had no statistical significance by Paired-Samples T Test (t=-1.780, P=0.084). By Bivariate-Pearson correlation, a negative correlation between DIOA and SFCT was found in preoperative group (r=-0.797,P<0.001). Also the postoperative DIOA and SFCT6months later were negative correlated significantly by Bivariate-Pearson Correlation (r=-0.647,P=0.001).Conclusions The postoperative DIOA decreased significantly compared with the preoperative but SFCT had no statistical difference. Pre-and postoperative DIOA and SFCT were negative correlated significantly in IMH eyes and this may suggest a contributing role of the choroid in the pathogenesis of idiopathic macular hole.