Hi
A normal diet without any sugary root veg, fruit and grain products is usually enough; except for the most severe cases. In milder to medium cases of diabetes, it generally disappears on its own again after a few months.
You can find some tips in the relevant chapter in this link here:
Long Term Balanced General And Special Needs Guinea Pig Diets
Regulr weight monitoring is also important in the case of a diagnosed diabetes:
Weight - Monitoring and Management
Cataracts are more likely congenital (i.e. due to an inherited genetic disposition when appearing in younger age) or they are mostly old age related. The vast majority of cataracts are actually not a symptom of diabetes although very occasionally they can be caused by it.
Thankfully, sight is the weakest guinea pig sense whereas it is the strongest in humans. The transition period - especially with very fast developing cataracts or nuclear sclerosis (where the lens goes opaque more evenly; cataracts are more like galaxy clusters that gradually grow) - is usually the most difficult until the other senses have adapted.
One of my fully blind cataract piggies even totally rebuilt her mind map of a fair bit of the garden and was able to continue to free roam with her mate (always under my supervision of course), including coming to me over the distance of several yards just with my vocal guidance.
Sight impeded guinea pigs can lead a perfectly normal life as long as you leave enough scent markers in the cage (don't deep clean furnishings at the same time as the bedding). The more you challenge them, the more qulity of life they will maintain/regain. Wrapping piggies losing their sight in cotton wool is the worst possible gift; rather rethink your piggy premises nd daily routine from the perspective of smell, touch and sound.
Guinea Lynx :: Eyes
Enrichment Ideas for Guinea Pigs
After an initial wave of over-diagnosis, yes, diabetes does occasinally in guinea pigs but it is actually not all that common. It is however good to have a possible link checked. All the best
