Residual Peripheral Fields in RP and the Risk for Pedestrian Collisions

Abstract

 

Purpose

 

People with advanced retinitis pigmentosa (RP) frequently report collisions with other pedestrians. Peripheral “islands” of vision, often retained in early stages of disease progression, may be helpful in avoiding collisions. We are developing a prism-based device intended to provide artificial residual islands. To achieve best results we need to know where these islands should be most useful. We computed the spatial distribution of collision risk in the visual field and compared it to the distribution of lateral residual Islands in patients.

 

Methods

 

For a collision to occur, a walking pedestrian must keep a fixed bearing with respect to the patient. We derived spatial maps of the risk of colliding with pedestrians starting at all locations and moving in all directions, while imposing realistic constraints on walking speeds and time to collision. Digitized Goldmann perimetry clinical data from 42 patients with residual islands were combined to construct a frequency distribution of percentage of patients with vision at each visual eccentricity.

 

Results

 

We found that the mid-periphery represents the highest relative collision risk. In patients, there are two peaks in the frequency distribution of horizontal seeing area; a nasal peak at 35^o eccentricity with a range at half height of 24^o-46^o, and a temporal peak at 54^o (range 35^o-73^o). There was a high degree of symmetry across fellow eyes.

 

Conclusions

 

The natural nasal residual fields overlap the areas of greatest collision risk (see fig.). Creating artificial islands of vision at these eccentricities for patients who have lost these natural islands should be most beneficial for this task.  

 

A map of relative collision risk with pedestrians coming from the right side of a patient. The red wedges show the range of pedestrian headings that lead to collisions with a patient who walks from (0, 0)m toward (0, 10)m at 1m/s. Only pedestrians colliding in ≤ 5s and walking 0.7-1.5m/s are shown. Thus, locations with the most red represent the most frequent starting locations of hazardous pedestrians. The grayscale background shading is derived from the distributions shown in the inset and encodes the percentage of patients in our sample (n=42) who have residual vision at each eccentricity (black=0%, white=100%) The inset shows the seeing areas of the left eye nasal field and the right eye temporal field.