Ritalin for treating attention and lack of focus in depression I’d like to know if there’s research about the use of ritalin for treating attention deficit in Major Depression Disorder.
Yes, there is 2014 review of Corp et al. on stimulants in the treatment of MDD (and bipolar). There is another 2015 review by Pary et al. just on stimulants in depression.

Some researchers reviewing this, e.g. Mahli et al. (2016) have been critical of this use of stimulants, on the argument that the effects appears to be short-lived:


  Clinically, the rapid amelioration of depressive symptoms with traditional psychostimulants is often dramatic but short-lived, and this suggests that they likely operate via different mechanisms to conventional antidepressants. More importantly, there is little evidence from randomised controlled trials supporting their efficacy in treating depression, although modafinil has been shown to be effective in reducing prominent depressive symptoms, such as fatigue. Research is urgently required to clarify psychostimulants’ mechanisms of action and to evaluate their long-term benefits and risks in the treatment of major and bipolar depression.


There aren't a lot randomized-control studies either.

UpToDate says


  Stimulants (eg, methylphenidate) are indicated for late-life, treatment-resistant unipolar major depression. In addition, stimulant-like drugs (eg, modafinil and pramipexole) have limited evidence for efficacy in the general population of patients with treatment-resistant major depression. The use of stimulants and stimulant-like drugs is consistent with multiple treatment guidelines [11-13]. Based upon our clinical experience, we are more inclined to use stimulants and stimulant-like drugs for patients who lack energy, drive, motivation, interest, optimism, pleasure, and the ability to initiate activities


I didn't review those guidelines cited (American Psychiatric Association's or CANMAT) to see if they really say that. The last review they mention there is a little older, from 2007.