Emsley FINCHAM's test

FINCHAM's test:--

it is a test used to determine whether a coloured halo originates from the lens (as in cataract) or from the cornea (as occurs in acute congestive glaucoma). 

A stenopic slit is passed across the pupil a lenticular halo will show a break in the halo, whereas a corneal halo will show reduced brightness (but no break) in the halo. 

Coloured halos:-

Rainbow 🌈 coloured rings around the light at night. 

It is seen due to Acute angle closure glaucoma, cataract, corneal edema, mucus on the surface of conjunctiva. 

• Occurs due to prismatic dispersion of light bought about these condition. 
• Occurs due to accumulation of fluid in the corneal epithelium, and to alternation in the refractive condition of the corneal lamellae. 
• Halos induced by corneal disease & early cataractous changes at the lens may be differentiated by FINCHAM's test. 

Corneal halos:-

Corneal halos due to corneal edema can be caused by increased intraocular pressure that forces the water in to the cornea producing water clefts, which acts as a diffractive particles. 

e.g. patients may report coloured haloes around small bright lights during episodes of acute glaucoma. 

Swimming in the chlorinated pools and overwear of contact lenses may give a similar effects. 

Lenticular haloes:-

Lens also has regularly arranged fibres. 

With the exception of zonular area and the anterior cellular area, it's fibres are laid out in a radial fashion. 

The axial part of the lens is uniform , so no halo is seen with small pupil diameters(<3mm). 

Under low light conditions or when dilated, the effects of the peripheral zone become apparent and a halo is seen. 

Stanopaeic slit:-

Stenopic slit consists of rectangular aperture ranging from 0.5 to 1.0mm in width and up to 15mm in length.
Stenopic slit reduces the size of blur circle in the meridian at the right angle to the slit, yet allows blur circle size to be unchanged in the meridian coincident with it. 

• FINCHAM's test is done using the stenopic slit to differentiated the coloured haloes caused by cataract (lenticular) from that caused by glaucoma(cornea) . 
•  Stenopic slit is moved across patient's eye while the patient looks at bright point light source of light which gives rise to halo. 
• The  halo caused by cataract breaks in to a fan the blades of which seems to move whereas the halo caused by glaucoma remains unchanged or just becomes a little faint . This is caused by peculiar deposition of the lens fibres which caused by diffraction of the light  parellel to them. 

Interpretation:- glaucomatous halo remains intact but diminished in intensity whereas the lenticular halo is broken up in to segments which revolves as the slit is moved.