A cataract is a clouding of the eye’s natural lens. Together with uncorrected refractive error, it is a leading cause of vision impairment and blindness worldwide [1]. The World Health Organization (WHO) attributes 94 million cases of addressable distance vision impairment or blindness to cataract, and reports that one in two people who need cataract surgery cannot access it [1,2].
Cataract develops slowly. Recognising cataract symptoms early, and recording lens changes in a consistent and objective way, gives patients and clinicians more time to plan care.
Cataract Symptoms and the Early Signs of Cataract
Early cataract is often silent. The US National Eye Institute (NEI) notes that a person may have no symptoms while a cataract is still mild [3]. As the opacity grows, the common cataract symptoms are:
- Cloudy or blurred vision that develops gradually and without pain
- Colours that look faded or yellowed
- Difficulty seeing at night
- Glare from lamps, sunlight or oncoming headlights, and haloes around lights
- Double vision, usually in one eye
- Frequent changes in spectacle or contact lens prescription [3,4]
These early signs of cataract are not specific to the condition. The NEI advises that the same symptoms can indicate other eye problems, so they call for a full eye examination and not self-diagnosis [3].
Nuclear vs Cortical vs Posterior Subcapsular Cataract and Why the Type Matters
Age-related cataract is classified by the part of the lens that becomes opaque. The three main types are nuclear, cortical, and posterior subcapsular, and each produces a different symptom pattern [4].
| Type | Location in the lens | Slit-lamp appearance | Typical complaint |
| Nuclear | Central nucleus | Yellow hue that deepens to brown in advanced cases, best seen with oblique illumination | Shift towards short-sightedness; some patients read again without spectacles (“second sight”) |
| Cortical | Outer cortex | Wedge-shaped or spoke-like opacities, often first seen in the inferonasal quadrant | Glare and light sensitivity |
| Posterior subcapsular | Just in front of the posterior capsule | Granular or plaque-like opacity that appears black and vacuolated on retroillumination | Glare, haloes and light sensitivity, with a marked effect on vision |
In the nuclear vs cortical cataract comparison, the key difference is how each one disturbs vision. Nuclear sclerosis raises the refractive index of the lens, so it changes the prescription first. Cortical opacities scatter light, so glare is the leading complaint [4]. A posterior subcapsular opacity sits close to the nodal point of the eye, which explains why a small opacity can affect vision profoundly [4].
Why the type matters. The type of cataract helps explain what a patient notices and how quickly vision may change. Nuclear and cortical cataracts usually progress slowly, while posterior subcapsular cataracts tend to progress faster and can affect vision early, even when the opacity is small. Type and density also matter for surgical planning: a very dense nuclear cataract is generally more demanding to remove than an early or cortical one [4]. This is why clinicians grade the type and severity of a cataract and record it consistently over time, rather than simply noting that a cataract is present.
What a Cataract Test Involves
There is no single cataract test. The diagnosis is clinical and is built from several steps [3,4]:
- Visual acuity. Vision is measured in each eye with a standard chart.
- Slit-lamp examination. The lens is examined under magnification, with the pupil both undilated and dilated. This is also where the cataract is graded, most commonly by comparing the lens against standard reference photographs, such as those in the Lens Opacities Classification System III (LOCS III) [5].
- Dilated fundus examination. The retina and optic nerve are checked, because other disease can limit vision after surgery.
- Ultrasound, when needed. If a dense cataract blocks the view of the retina, ultrasound is used to rule out posterior segment disease.
The NEI recommends a dilated eye examination every one to two years from the age of 60 [3].
Cataract Grading and How Clinicians Score Severity
Cataract grading turns a visual impression into a score that can be recorded, compared, and tracked. The most widely used system is the Lens Opacities Classification System III (LOCS III), which reviewers describe as the reference standard [5,11].
In LOCS III, the examiner compares the patient’s lens with a set of standard photographs [5]:
- Nuclear opalescence (NO) and nuclear colour (NC). Six slit-lamp reference images, graded on a decimal scale from 0.1 to 6.9.
- Cortical cataract (C). Five retroillumination reference images, graded from 0.1 to 5.9.
- Posterior subcapsular cataract (P). Five retroillumination reference images, graded from 0.1 to 5.9.
Two simpler systems are used where speed and minimal training matter. The WHO simplified cataract grading system uses three severity levels for each cataract type and was designed for field surveys by relatively inexperienced observers [6]. The Age-Related Eye Disease Study (AREDS) clinical lens grading system also relies on standard photographs and needs little examiner training [7].
All of these systems share one limitation. The grade depends on the examiner’s judgement, so repeatability varies with experience [10,11].
Why Anterior Segment Imaging Matters
Anterior segment imaging adds an objective, permanent record to a subjective grade. It supports cataract care in three ways.
It makes grading reproducible. LOCS III itself is built on slit-lamp and retroillumination photographs [5]. A captured image can be graded again, reviewed by a second clinician or shared for a remote opinion.
It quantifies lens density. In a study of 180 eyes with nuclear cataract, lens density measured by Scheimpflug imaging rose linearly with the LOCS III nuclear opalescence score. It also correlated more strongly with visual acuity than the LOCS III scores did [8]. Swept-source optical coherence tomography (SS-OCT) also measures lens density reproducibly. In 110 eyes, average lens density was repeatable and separated cataract from clear lenses with 73.9% sensitivity and 91.2% specificity [9].
It may inform surgical planning. In a study of 1,222 eyes, nuclear density measured on swept-source anterior segment OCT correlated with LOCS III nuclear opalescence scores (r = 0.712) and identified hard nuclear cataract with an area under the curve of 0.859 [10].
Imaging does not need to be complex to be useful. A slit lamp with a camera module, such as the 3nethra SL5-1000 with its optional 24.1-megapixel imaging system, lets a clinic document the lens at every visit and track change against a baseline [12].
Imaging supports clinical judgement and does not replace it. The decision to operate still rests on how far the cataract interferes with daily activities such as reading and driving [3].
Conclusion
Cataract symptoms begin subtly, with glare, faded colours and a changing prescription, and they differ by cataract type. A structured examination and a recognised grading system such as LOCS III give each lens a score that can be followed over time. Anterior segment imaging adds an objective measure to that score, which helps clinicians track change more consistently and support surgical planning.
This article is for general information and does not replace an examination by a qualified eye care professional.
References
- World Health Organization. Blindness and vision impairment. Fact sheet. 10 February 2026. who.int
- World Health Organization. One in two people facing cataract blindness need access to life-changing surgery. News release. 11 February 2026. who.int
- National Eye Institute. Cataracts. Last updated 15 November 2023. nei.nih.gov
- Nizami AA, Gurnani B, Gulani AC. Cataract. In: StatPearls. Treasure Island (FL): StatPearls Publishing; updated 27 February 2024. NBK539699
- Chylack LT Jr, Wolfe JK, Singer DM, et al. The Lens Opacities Classification System III. Arch Ophthalmol. 1993;111(6):831-836. doi:10.1001/archopht.1993.01090060119035
- Thylefors B, Chylack LT Jr, Konyama K, et al. A simplified cataract grading system. Ophthalmic Epidemiol. 2002;9(2):83-95. Record
- Chew EY, Kim J, Sperduto RD, et al. Evaluation of the Age-Related Eye Disease Study clinical lens grading system: AREDS Report No. 31. Ophthalmology. 2010;117(11):2112-2119.e3. PMC2944007
- Pei X, Bao Y, Chen Y, Li X. Correlation of lens density measured using the Pentacam Scheimpflug system with the Lens Opacities Classification System III grading score and visual acuity in age-related nuclear cataract. Br J Ophthalmol. 2008;92(11):1471-1475. bjo.bmj.com
- Panthier C, Burgos J, Rouger H, Saad A, Gatinel D. New objective lens density quantification method using swept-source optical coherence tomography technology: comparison with existing methods. J Cataract Refract Surg. 2017;43(12):1575-1581. Record
- Wang W, Zhang J, Gu X, et al. Objective quantification of lens nuclear opacities using swept-source anterior segment optical coherence tomography. Br J Ophthalmol. 2022;106(6):790-794. doi:10.1136/bjophthalmol-2020-318334
- Mackenbrock LHB, Labuz G, Baur ID, Yildirim TM, Auffarth GU, Khoramnia R. Cataract classification systems: a review. Klin Monbl Augenheilkd. 2024;241(1):75-83. doi:10.1055/a-2003-2369
- Forus Health. 3nethra SL5-1000 slit lamp. Product specifications. forushealth.com
