The Distribution of Spatial Contrast in Manmade Environments Produces Regional Visual Form Deprivation.

PURPOSE

Children who spend less time outdoors or who live in urban areas are more likely to develop myopia (short-sightedness). This may stem from the altered spatial distribution of contrast in manmade environments, which contain large featureless surfaces that may potentially produce regional environmental form deprivation (eFD).

METHODS

Images (n = 590) from natural, mixed-urban, urban, and indoor environments, were subdivided into 36 × 36 zones (1.6° × 1.2° visual angle). The weighted contrast energy (CEw) of each zone was calculated by filtering the fast Fourier transform with a filter describing the contrast sensitivity of the human retina at that eccentricity. Zones with less CEw than in images taken through white Perspex ocular diffusers that induce form-deprivation myopia in guinea pigs were classified as eFD. The spatial complexity of CEw signals across the visual field were compared among the environments.

RESULTS

Featureless manmade structures such as blank walls, ceilings, and roads contain low CEw and thus cause regional eFD, particularly when present in the peripheral retina where spatial resolution is low. Based on the images analyzed from indoor environments, 29.5% of the human visual field would potentially experience eFD, a percentage greater than that likely experienced in outdoor urban (15.2%, P < 0.001), mixed-urban (6.7%, P < 0.001), and natural (2.8%, P < 0.001) environments. The complexity of the contrast energies perceived across the visual field were also significantly less in indoor environments than in all other settings, meaning eye movements are less likely to result in a change in contrast, thus regional eFD is more likely to be temporally maintained. Furthermore, this effect was exaggerated in the visual periphery during gaze-limiting tasks such as reading or using a mobile phone.

CONCLUSIONS

Widespread eFD is potentially experienced across the visual field in manmade environments. The extensive peripheral eFD and diminished contrast complexity of manmade environments suggest that gaze-limiting activities such as reading or using a mobile phone result in extended periods of peripheral eFD, which may contribute to myopia development. Therefore, enhancing the distribution of contrast in artificial environments to limit regional eFD may serve to prevent myopia onset.