Optical assemblies comprising an optical device and a composition comprising a resin-linear organosiloxane block copolymer are disclosed. In some embodiments, the organosiloxane block copolymers has a weight average molecular weight of at least 20,000 g/mole and includes 40 to 90 mole percent disiloxy units of the formula [R12SiO2/2] arranged in linear blocks each having an average of from 10 to 400 disiloxy units [R12SiO2/2] per linear block, 10 to 60 mole percent trisiloxy units of the formula [R2—SiO3/2] arranged in non-linear blocks each having a weight average molecular weight of at least 500 g/mol, and 0.5 to 25 mole percent silanol groups. R1 is independently a C1 to C30 hydrocarbyl and R2 is independently a C1 to C20 hydrocarbyl. At least 30% of the non-linear blocks are crosslinked with another non-linear block and aggregated in nano-domains. Each linear block is linked to at least one non-linear block.