Diagnosis
Classifications
There are typically four classes (or types) of PFFD, ranging from class A to class D, as detailed by Aitken.Types of PFFD 
Type A — The femur bone is slightly shorter on the proximal end (near the hip), and the femoral head (the ball of the thigh bone that goes into the hip socket) may not be solid enough to be seen on X-rays at birth, but later hardens (ossifies). This deformity is sometimes called congenital short femur, because the child’s anatomy from hip to knee is contiguous and similar to their peers except for the one shortened bone. In some cases, children with type A deformities will also have an externally rotated femur, which could lead to bowing of the legs (genu varum). Type B — The femur bone is shorter on the proximal end (near the hip) and the defect affects both the femoral head (the ball) and the femoral shaft (the long part of the bone). This defect is more severe than type A deformities because it will not heal spontaneously and, at skeletal maturity, the proximal femur (lower part near the knee) will not connect with the femoral head. Type C — The entire top half of the femur bone is absent, including the trochanters (the part of the bone in which muscles are attached to the upper thigh), and the femoral head. In type C deformities, the proximal femur is not connected to the hip in any way.
Basic testing for scotopic sensitivity was tried by optometrists, opticians and orthoptists in UK hospitals, and by optometrists and opticians in private practice employing a technique that used the Intuitive Colorimeter, developed under Medical Research Council licence. An alternative approach to correct Irlen syndrome was tried by Orthoscopics franchise in the UK, with wide colour coverage and tints manufactured by Hoyato match. Other commercial organisations have produced sets of therapeutic tints, although most have not received scientific evaluation.Studies investigating Irlens syndrome as a treatable condition have been criticised for having a biased and subjective approach to their research.Treatments offered by Irlens practitioners have not been found to be effective in improving reading ability. Classifications
Irlen divides Irlen syndromes into six types: photophobia, distortion of the fundus, graphical distortions during reading, decreased visual field, difficulty in ocular fixation during reading and change in depth perception. Research
The disorders have been studied in several institutions, including the Psychology Department at Essex University, the former Applied Psychology Unit, Cambridge University in England, and in the case of Meares-Irlen syndrome, Visual Unit at Glasgow Caledonian University in Scotland. As of 2012 the Visual Stress Unit offered non-commercial diagnostic and therapeutic services to individuals, and provided advice to the Scottish National Health Service. In Australia, Irlen syndrome was researched by Paul Whiting at the University of Sydney. Whiting set up the first Irlen Dyslexia Centre in Australia, which operated in the Childrens Centre at Sydney University for more than 15 years.