In general, the ABs have little effect on visual function, and it is rare to treat AH with vitreous surgery. The reason why the subjective symptoms such as decreased vision or floaters rarely occur in eyes with AH is that the density of ABs in the vitreous cavity is relatively low . In addition, the ABs are present only in the vitreous gel and are not present in the liquid vitreous, Cloquet’s canal, or posterior to a vitreous detachment . In our case, it is unclear whether the PVD existed before the cataract surgery, but it is more likely that the cataract surgery caused the PVD . We suggest that the visual impairment developed because the PVD forced the residual vitreous to move to the anterior vitreous cavity. This resulted in concentrating the ABs in the anterior vitreous cavity closer to the nodal point of the eye.
Even when the fundus visibility is poor in eyes with AH, it is common for the fluorescein angiographic and OCT images to be clear [6, 7]. In particular, OCT is excellent at detecting macular diseases such as age-related macular degeneration, epiretinal membrane, macular hole, and CME in eyes with AH which are all difficult to detect ophthalmoscopically. Moreover, OCT is quite useful for detecting the changes that cause the vision reduction in AH patients.
In our patient, clear SD-OCT images of the retina could not be obtained prior to the vitreous surgery. We suggest that this was because the ABs were so concentrated in the anterior vitreous cavity near the nodal point that not enough light could pass through the ABs to form a sharp tomographic image. Although the CME may have also caused some of the decreased VA in this eye, the vision did improve significantly despite the presence of the CME after the surgery. Thus, the concentrated ABs in the anterior vitreous were the more likely cause of the reduced vision. However, the true extent of the vision being affected due to asteroid hyalosis may be difficult to explain due to the inability to image the macula before the vitrectomy.
There have been several reports of AH cases in which the BCVA improved after vitreous surgery [8,9,10]. However, only a few of these studies reported on the exact cause of the reduced vision prior to the surgery. Jingami et al. reported on a AH patient with retinitis pigmentosa who had a decrease in the VA after cataract surgery . Just as in our case, there was a significant improvement of the VA after vitreous surgery. They suggested that the cause of the decreased VA after the cataract surgery was that changes in the AB distribution caused by a change in the shape of the vitreous body due to the cataract surgery. However, it was reported that the posterior vitreous body was not detached when it was examined during vitreous surgery [12, 13]. Reviewing the published cases in which vision was improved by vitreous surgery, we were unable to find publications where the posterior vitreous was clearly detached as it was in our case.
The posterior vitreous is usually not detached in eyes with AH, and in cases of AH accompanied by advanced diabetic retinopathy in particular, there are many cases of extremely strong vitreoretinal adhesions and surgery is known to be very difficult . Mochizuki et al. found that even in AH cases where it initially appeared that a PVD was present, it was common for the vitreous cortex to be found in the posterior retina and for vitreoschisis to be present . However, even in AH cases, there are cases such as our case in which a complete PVD had occurred and the ABs were concentrated in the anterior vitreous. Thus, we suggest that in such cases vitreous surgery should be performed especially if the VA is reduced.