• Cataract surgery is commonly performed in elderly patients who are at high risk for developing postoperative cognitive dysfunction. Most cataract surgeries are performed under peribulbar or retrobulbar anesthesia, however, most of the patients require sedation to relieve the perioperative anxiety and induce amnesia. So, many sedative agents can be used especially benzodiazepines which may increase the risk of developing postoperative cognitive dysfunction.
• Ketamine can be used as a sedative and analgesic agent in a dose of 0.25 -0.5 mg/kg with certain studies suggesting that it may decrease the risk of postoperative cognitive dysfunction. Similarly, dexmedetomidine can be used as a sedative and analgesic agent with the possibility of decreasing the incidence of postoperative cognitive dysfunction.
• this controlled study will compare the effect of ketamine or dexmedetomidine on the POCD of patients undergoing cataract surgery.

• Postoperative cognitive dysfunction is a common postoperative complication in elderly patients. Despite the role of the risk of anesthesia and/or surgery in developing postoperative cognitive dysfunction, it can be developed even with surgeries performed under local or regional anesthesia.
• Ageing is the most common risk factor for developing postoperative cognitive dysfunction that can affect memory and speech. Also, impaired vision may be another important risk factor.
• Cataract surgeries can be considered the most common surgery performed in elderly patients. It is usually performed under local anesthesia (peribulbar, retrobulbar, or sub-tenon blocks), however, sedation is usually required to relieve the anxiety of the patients and induce amnesia.
• there are many sedative agents that can be used with such patients, the most commonly used are benzodiazepines. However, benzodiazepines use may increase the incidence of postoperative cognitive dysfunction.
• Ketamine, the dissociative anesthetic, acts mainly through inhibition of NMDA receptors that reduce the neuronal loss of the cortex. it may attenuate the postoperative cognitive dysfunction and induce neuroprotective effect through suppressing the inflammatory response and minimizing cerebral ischemia.
• dexmedetomidine is a sedative and analgesic agent that have the advantage of minimal respiratory depression and can be used as a sedative agent in cataract surgery. Studied revealed that its sedative analgesic effect is not associated with changes in memory.
• This randomized controlled double-blinded study will be carried upon 90 elderly patients undergoing cataract surgery under peribulbar anesthesia where they will be classified into 3 groups: - Group I (Placebo Group). Where the patients will receive normal saline as a placebo.

Group II (Ketamine group). Where patients will receive ketamine in a dose of 0.3 mg/kg in physiological solution.

Group III (Dexmedetomidine group). where patients will receive dexmedetomidine in a dose of 0.5 ug/kg in a physiological solution.

-Primary outcome will be the incidence of POCD, the secondary outcomes will be the hemodynamic changes and the changes in the intraocular pressure.

Inclusion Criteria:

• Patients aged more than 65 years presented for cataract surgery under peribulbar anesthesia.

Exclusion Criteria:

• Patients with a history of psychological disorders as psychosis, schizophrenia, nephropathy.
• Patients with uncontrolled medical conditions as D.M and hypertension.
• Known allergy to the used medications
• patients with hepatic, renal, or heart failure
• Patients receiving anti-psychotic or anti-depressant medications.

The data of the primary outcome will be available with the corresponding author till 6 months after approval of the publication of the trial.

till 6 months after approval of the publication of the trial.

Contact the principle investigator

• The patients will be blinded to their groups.
• An anesthesia resident who will not participate in the study and have no the subsequent rule in it will help in the preparation of local anesthetic mixtures under strict aseptic precautions.
• An assistant nurse who will be blinded to the study groups and will have no the subsequent rule in it will help in the collection of the data of measurements