\[ \boxed { xy \left ( x \right ) {\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left ( x \right ) + \left ( {\frac {ax}{\sqrt {{b}^{2}-{x}^{2}}}}-x \right ) \left ( {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) \right ) ^{2}-y \left ( x \right ) {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) =0} \]
Mathematica: cpu = 0.075510 (sec), leaf count = 55 \[ \left \{\left \{y(x)\to c_2 \exp \left (\frac {c_1 \log \left (a \sqrt {b^2-x^2}-c_1\right )}{a^2}+\frac {\sqrt {b^2-x^2}}{a}\right )\right \}\right \} \]
Maple: cpu = 3.182 (sec), leaf count = 50 \[ \left \{ y \left ( x \right ) ={\it \_C2}\,{{\rm e}^{\int \!-{x\sqrt {{b }^{2}-{x}^{2}} \left ( a{b}^{2}-a{x}^{2}+{\it \_C1}\,\sqrt {{b}^{2}-{x} ^{2}} \right ) ^{-1}}\,{\rm d}x}} \right \} \]