Programmatically make a proximity search with Solr

I'm using Search Api Solr to do programatic searches with the following example code. How can I include a proximity search with this approach? I'm looking through the code but I'm not seeing it.

I'm using geofield and the latlng is being indexed correctly by solr and can make a direct filter with it, but need proximity.

Any help would be great!

Current code:

$index = search_api_index_load('solr_index');
$query = $index->query();
$query->keys('My search term');

$filter = $query->createFilter('OR');
$filter->condition('field_my_field', 'value');
$query->filter($filter);
$results = $query->execute();