The College of Optometrists

are diabetics more difficult to dilate, and if so why?

Not really they use Phenylepherine in combination with tropicamede to get maximum dilation to dilate diabetics in the hospital, In practice i tend to use tropicamide only as i find it sufficient.

I think they tend to have smaller pupils to begin with so the net dilation with tropicamide is less.

Diabetics may not dilate as well as normal, due to a peripheral neuropathy (In T1 diab, affect of parasymp.=symp., in T2 diab, affect of parsymp.>symp.). However, they generally dilate adequately with tropicamide, even 0.5%. Possibly because most drops overkill the amount of drug needed anyway.

If problems, with tropicamide alone. Rather than use an additional drop of the same drug, better to use 2.5%phenylephrine - as the effect of the parasympathetic system may be near saturation, so more efficient to work on the sympathetic system. Also, added benefit of synergism.

n.b. due to denervation, some diabetics are hypersensitive to sympathomimetics

Also remember alot of diabetics have peripheral vaculr disease so use phenylephrine with caution.

If inadequate dilation possible refer for furthter opinion if retinopathy suspected.