This retrospective study aimed to identify the pattern of visual impairment in pituitary adenoma patients. Patients' eyes were categorized into four groups according to their visual acuity score. Trans-sphenoidal hypophysectomy was performed on all patients. Significant differences between groups were evaluated for visual field defects, visual symptoms duration, degree of suprasellar extension and tumour pathology. In the 201 patients (402 eyes) evaluated, 166 eyes had impaired visual acuity (45 eyes, < 4.0; 43 eyes, 4.0 - 4.4; and 78 eyes, 4.5 - 4.8), 236 eyes scored > 4.8 and were considered to be free of this disorder. A linear correlation was found between visual field defects and visual acuity score. Duration of visual symptoms between visual acuity groups was not significant. Suprasellar extension (measured by Hardy grades) was significant between visual acuity groups and may be the main cause of visual acuity loss in pituitary adenoma patients. Non-functional pituitary adenomas tended to affect visual acuity more than adenomas with other pathological diagnoses which are adrenocorticotropic hormone and prolactin. Further investigation is required to clarify visual loss cause in pituitary adenoma patients.