| Myopia | Eye (vision) | Elongated eyeball OR excessive corneal/lens curvature → image in front of retina | Cannot see distant objects clearly | Concave (diverging) lens |
| Hypermetropia | Eye (vision) | Short eyeball OR flat cornea/lens → image behind retina | Cannot see near objects clearly | Convex (converging) lens |
| Presbyopia | Eye (lens) | Age-related loss of lens elasticity → reduced accommodation | Cannot focus on near objects (affects people over 40) | Bifocal lenses |
| Astigmatism | Eye (cornea) | Irregular curvature of cornea (or lens) → different focal points | Blurred/distorted vision at all distances | Cylindrical lens |
| Cataract | Eye (lens) | Opacification (clouding) of lens — aging, UV, diabetes | Progressive painless blurred vision | Surgical lens replacement |
| Glaucoma | Eye (optic nerve) | Elevated intraocular pressure → optic nerve damage | Progressive peripheral vision loss → tunnel vision → blindness | Eye drops (beta-blockers) or surgery |
| Night blindness | Eye (rods) | Vitamin A deficiency → rhodopsin insufficiency | Cannot see in dim light | Vitamin A supplementation |
| Conductive deafness | Ear (ossicles) | Otosclerosis (stapes fixation), perforated tympanic membrane | Hearing loss; bone conduction preserved | Surgery, hearing aids |
| Sensorineural deafness | Ear CNVIIIcochlea | Hair cell damage (noise, age), auditory nerve damage | Hearing loss; bone conduction also affected | Cochlear implants |
| Parkinson's disease | CNS (substantia nigra) | Loss of dopaminergic neurons → dopamine deficit | Resting tremor, rigidity, bradykinesia | L-DOPA |
| Multiple sclerosis | CNS (myelin) | Autoimmune demyelination of CNS (oligodendrocytes) | Variable: weakness, ataxia, optic neuritis | Immunomodulatory drugs |
| Myasthenia gravis | NMJ | Autoantibodies against nicotinic ACh receptors | Fatigable muscle weakness, ptosis, diplopia | AChE inhibitors |
| Alzheimer's disease | CNS (cortex, hippocampus) | Amyloid plaques, neurofibrillary tangles; ACh system affected | Memory loss, cognitive decline | Symptomatic (AChE inhibitors) |
| Epilepsy | CNS (widespread) | Neuronal hyperexcitability (GABA deficit or glutamate excess) | Seizures (tonic-clonic, absence) | Anti-epileptics (enhance GABA) |
| Depression | CNS (monoamine systems) | Low serotonin (±norepinephrine, dopamine) | Persistent low mood, anhedonia | SSRIs, SNRIs |