Per the current documentation for 2dsphere indexes, queries using $near and $nearSphere require a GeoJSON point passed to them, but otherwise work normally. However, $near and $nearSphere queries against a field with a 2dsphere index return no results if a $maxDistance parameter is provided.
e.g.
db.random.find( {geometry: { $nearSphere:
}})
returns results, but
db.random.find( {geometry: { $nearSphere:
{type:"Point", "coordinates":[-83,40]}, $maxDistance: 10}})
does not.