In Japan, cataracts is managed by ophthalmologists. A cataract is a clouding of the crystalline lens of the eye that causes painless, progressive loss of vision and is the single leading cause of blindness worldwide. The Global Burden of Disease 2020 estimates 100 million people have moderate-to-severe vision impairment from cataract and 17 million are blind from untreated cataract, with the heaviest burden in South Asia, sub-Saharan Africa, and Latin America where surgical access is limited.
A cataract (ICD-10: H25 age-related, H26 other, H28 cataract in diseases classified elsewhere) is an opacification of the crystalline lens of the eye, the biconvex transparent structure behind the iris that focuses light onto the retina. With age, lens proteins (crystallins) undergo oxidative modification, cross-linking, and aggregation, producing progressive loss of transparency. The clinical classifications of age-related cataract are: nuclear sclerotic (the most common, in which the central nuclear lens darkens and yellows, producing 'second sight' myopia and gradual visual loss); cortical (spoke-like cortical opacities radiating from the equator into the visual axis, often with glare and difficulty in bright sunlight); posterior subcapsular (a plaque-like opacity beneath the posterior lens capsule that disproportionately impairs near vision and produces marked glare, often appearing earlier in life and accelerated by corticosteroid use, diabetes, or radiation); and anterior subcapsular and mixed cataracts (combinations of these features). Beyond age-related cataract, congenital cataract (present at birth, often from genetic mutations, intrauterine infection, or metabolic disease), pediatric cataract (developing in childhood), traumatic cataract (after blunt or penetrating ocular injury), iatrogenic cataract (after intraocular surgery or systemic corticosteroid use), and metabolic cataract (in diabetes, galactosemia, Wilson disease) account for the remaining cases.
The key symptoms of Cataracts are: Gradual, painless, progressive blurring of vision over months to years that does not fully improve with glasses., Increased glare and halos around lights, particularly at night when driving or reading., Dimming or yellowing of colors — patients often report colors appearing 'faded' or 'duller' compared with the unaffected eye or with how they remember them., Difficulty reading small print despite previously functional reading glasses; frequent prescription changes that fail to maintain clear vision., Second-sight myopia: temporary improvement in near vision in nuclear sclerotic cataract — patients sometimes report being able to read without glasses for the first time in years, soon followed by further deterioration., Monocular diplopia (double vision in one eye) from refractive irregularity within the cataract., Difficulty driving at night because of headlight glare and inability to see contrast against bright lights..
Diagnosis of cataract is straightforward and based on history of progressive painless visual loss with characteristic slit-lamp examination findings. An ophthalmologist or optometrist examines the lens after dilating drops (tropicamide 1% or phenylephrine 2.5%) using a slit-lamp biomicroscope, which provides magnified illumination of the lens. The lens is graded using the Lens Opacities Classification System III (LOCS III) for nuclear color, nuclear opalescence, cortical, and posterior subcapsular changes, providing standardized documentation and progression tracking. Visual acuity is measured with a Snellen chart in standard illumination and with glare testing (brightness acuity testing, BAT) which often reveals greater visual impairment than Snellen alone. Contrast sensitivity testing (Pelli-Robson, CSV-1000) detects subtle disability that standard acuity misses. Color vision testing (Ishihara, Farnsworth D-15) documents the yellowing effect of nuclear sclerosis. Optical coherence tomography (OCT) of the macula and optic nerve is performed before cataract surgery to exclude coexisting macular pathology (macular degeneration, epiretinal membrane, diabetic macular edema) that would limit post-operative visual outcome. Intraocular pressure measurement excludes glaucoma. Biometry (optical or ultrasound) measures axial length, corneal curvature, and anterior chamber depth to calculate the appropriate intraocular lens power for surgery. Corneal topography or tomography assesses regular and irregular astigmatism for toric IOL selection. Endothelial cell count (specular microscopy) is performed in patients with corneal opacities or prior surgery. Once the cataract is significant enough to limit lifestyle, work, or driving, surgery is offered. There is no specific 'visual acuity threshold' — surgery is offered based on functional impact, not a fixed Snellen line.
The prognosis of cataract is excellent. With modern phacoemulsification surgery and high-quality intraocular lens implantation, over 95% of patients in the absence of coexisting ocular pathology achieve 6/12 (20/40) or better visual acuity, restoring driving vision and reading function. Patients with coexisting macular degeneration, diabetic retinopathy, glaucoma, or other eye disease have outcomes limited by the additional condition rather than by the cataract surgery itself. The most common late complication is posterior capsule opacification (PCO) developing in 20-40% within 5 years, easily treated with Nd:YAG laser capsulotomy. Endophthalmitis remains the most feared complication at 0.05-0.1% in modern series with intracameral antibiotic prophylaxis. Retinal detachment occurs in roughly 0.5-1% over 10 years post-cataract surgery, with higher risk in highly myopic eyes. Refractive outcomes have improved substantially with modern biometry — over 80% of patients achieve refractive accuracy within ±0.5 D of target. Pediatric cataract operated within weeks of detection followed by intensive amblyopia therapy can achieve good visual outcomes; delayed surgery (after 6 weeks for unilateral disease, beyond infancy for bilateral) results in permanent deprivation amblyopia. WHO and IAPB target cataract elimination as a leading cause of blindness through expanded surgical access and high-volume programmes such as Aravind, LV Prasad, and Sightsavers.
Diagnosis and surgical management of cataracts is the province of ophthalmology. An optometrist or general ophthalmologist makes the initial diagnosis; cataract surgery is performed by an ophthalmologist with subspecialty training in cataract and refractive surgery. Pediatric cataract requires referral to pediatric ophthalmology. Patients with coexisting glaucoma, retinal disease, or corneal disease benefit from combined subspecialty input.
Find specialists →Immediate post-operative recovery: vision often improves within hours; return home same day. Day 1: substantial visual improvement in most patients. Week 1: vision continues to improve and stabilize; eye drops continue. Week 2: most activities can resume. Week 4-6: surgery considered fully healed; second eye surgery can be scheduled. Final refractive outcome and glasses prescription typically stable by 6 weeks. PCO if it occurs is treated with Nd:YAG laser at any later time.
Regular physical activity is encouraged. After cataract surgery, avoid heavy lifting (over 5-10 kg) for 1 week, swimming and saunas for 2 weeks, and contact sports for 4 weeks. Walking, light cycling, and gentle yoga can resume the day after surgery. Resume normal activity from 4 weeks with surgeon approval.
Choose an ophthalmologist who performs at least 200 cataract operations per year and reports outcomes (visual acuity, complication rates, refractive accuracy). Look for board certification, fellowship training in cataract and refractive surgery for complex cases, and use of modern equipment (femtosecond laser, advanced biometry, premium IOLs as needed). For pediatric cataract, choose a pediatric ophthalmologist.
Medically reviewed by AIHealz Medical Editorial Board · May 13, 2026
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