Retinoblastoma is the most common intraocular malignancy basically occurs among children below five. Certain ocular treatments such as surgery, radiation therapy and chemotherapy are more likely to cause side effects. Here, a rapid method of synthesising silver nanoparticles (AgNPs) from the brown seaweed Turbinaria ornata and its cytotoxic efficacy against the retinoblastoma Y79 cell lines was studied. The AgNPs synthesis was determined by Ultraviolet-visible spectroscopy and was further characterised by X-ray diffraction, High-resolution transmission electron microscopy, zeta potential, Energy-dispersive X-ray spectroscopy, thermogravimetric analysis, Fourier transform infrared spectrum and inductively coupled plasma-mass spectroscopy techniques. The synthesised AgNPs were found to be very stable and finely dispersed. The total phenolic content of the synthesised AgNPs was estimated at 43±2.52 mg/g gallic acid equivalent and the nanoparticles exhibited good scavenging activity analysed by 2, 2'-azinobis-(3-ethylbenzothiazoline-6-sulphonic acid) assay. Moreover, cytotoxicity of synthesised AgNPs against in vitro retinoblastoma Y79 cell lines showed a dose-dependent response with an inhibitory concentration (IC50) of 10.5 μg/mL. These results suggest that AgNPs could be a promising anticancer agent with enhanced activity in ocular treatment.