We read with interest the article by Noda and associates, which evaluated the impact of cataract surgery on subfoveal choroidal thickness and central retinal thickness in the elderly. The authors reported that surgery for senile cataracts increased subfoveal choroidal thicknesses, and the increase persisted for as long as 6 months postoperatively. These findings provide insights into the potential roles the choroid may play in the development of pseudophakic cystoid macular edema and the possible progression of age-related macular degeneration following cataract surgery.
A potential study limitation is that the authors measured choroidal thickness at a single point subfoveally. The choroid is a complex 3-dimensional structure with a highly anastomosed vessel network, and significant topographic variations of choroidal thickness at the macula have been reported. The choroid is thickest either subfoveally or in the temporal or superior sectors, and is thinnest nasal to the fovea. Ohsugi and associates had also reported that the increase in choroidal thickness following cataract surgery was the greatest in the inferior sector, followed by the foveal and nasal sectors. The increase in choroidal thickness was slight temporally and superiorly. It is possible that some choroid regions are more sensitive to inflammatory and metabolic changes following cataract surgery.
It may be useful to measure choroidal thickness at different macular regions, for example, at different distances from the fovea both vertically and horizontally. Measuring mean choroidal thickness and volume of predefined sectors using the Early Treatment Diabetic Retinopathy Study (ETDRS) grid are also more useful means of providing comprehensive information on the change of choroidal topography following cataract surgery than single-point thickness measurements.
The authors reported using image registration and tracking. This, in addition to diurnal variation of choroidal thickness, is an important consideration in longitudinal studies of optical coherence tomography (OCT) scans because of the topographic variation of choroidal thickness. A small change of the OCT scan position may result in changes in choroidal thickness that may appear to be real. Image registration and tracking will allow subsequent OCT scans to be performed at the same location.
In addition, the authors rightfully pointed out that one limitation was that they did not rule out the effect of the changed refraction following cataract surgery on the measured retinal and choroidal thickness. Cataracts cause media opacities that will increase light scattering and absorption, whereas clear optical media afforded by the cataract surgery will optimize forward and back light scattering. As spectral-domain optical coherence tomography (SD OCT) was used, the influence of cataract severity on the visualization of the chorioscleral boundary and choroidal thickness measurements may be small. However, it will also be interesting to know if poor OCT images attributable to severe cataracts were excluded from the analysis. With the introduction of swept-source OCT (SS OCT), clearer visualization of the chorioscleral boundary is possible. Studies have demonstrated good correlations between choroidal thickness measurements using SS OCT and SD OCT.
In summary, we congratulate the authors on their results, which add to our understanding of the factors affecting choroidal thickness following cataract surgery.