Eye as an Optical System & Ocular Anatomy

A comprehensive set of Q&A flashcards covering core concepts from the notes on the eye as an optical system and ocular anatomy.

What is Emmetropia?

Zero refractive error where parallel light forms a sharp image on the retina without the need for accommodation; normal eye power ~60 D and axial length ~22.22 mm.

What is Ametropia?

A refractive error where the image does not form on the retina; includes myopia, hyperopia, astigmatism, and combinations.

What is Myopia?

Near-sightedness where distant objects appear blurry; corrected with a concave (minus) lens; can be axial (long eye) or refractive (steep cornea/lens).

What is Axial Myopia?

Myopia caused by an eye that is longer than normal (axial length > 22.22 mm), causing the image to focus in front of the retina.

What is Refractive Myopia?

Myopia due to excessive optical power leading to the image focusing in front of the retina; often described by a minus prescription.

What is Simple Myopic Astigmatism?

One focal line in front of the retina and one on the retina; example: plano/−0.50 DCX 180.

What is Compound Myopic Astigmatism?

Both principal meridians focus in front of the retina (two focal lines in front of retina).

What is Simple Hyperopic Astigmatism?

One focal line behind the retina and one on the retina; example: plano/+0.50 DCX 180.

What is Compound Hyperopic Astigmatism?

Both focal lines behind the retina (two behind).

What is Mixed Astigmatism?

One focal line in front of the retina and the other behind the retina.

What is With-the-Rule Astigmatism?

Most powerful meridian is vertical (90°); axis is horizontal (180°).

What is Against-the-Rule Astigmatism?

Most powerful meridian is horizontal (180°); axis is vertical (90°).

What is Oblique Astigmatism?

Most powerful meridian is neither 90° nor 180° and is offset by more than 15° from those axes.

What is Regular vs Irregular Astigmatism?

Regular: principal meridians are at 90° to each other; Irregular: principal meridians are not 90° apart.

What is Anisometropia?

Significant difference in refractive error between the two eyes (typically ≥1.50 D spherical or ≥1.00 D cylindrical); antimetropia is one eye myopic and the other hyperopic.

What is Accommodation?

The process by which the eye increases its refractive power to view near objects, involving the ciliary muscle, zonules (Zinn’s), and the lens.

What triggers the stimulus to accommodation?

A blurry image or a near object prompts the eye to increase power to focus on the retina.

What are the Types of Accommodation?

Reflex accommodation, Tonic accommodation, Convergence accommodation, Proximal accommodation, and accommodation associated with the dark (dark focus).

What is the Amplitude of Accommodation?

The maximum accommodative power the eye can exert to clear a near object; measured in diopters as the difference between the far point and the near point.

What factors affect the Amplitude of Accommodation?

Original refractive status, general health, vascular/glandular status, age/presbyopia, drugs, convergence issues, and method of measurement.

What are common Anomalies of Accommodation?

Accommodative insufficiency, accommodative infacility, ill-sustained accommodation, accommodative spasm/excess, unequal accommodation.

What is Presbyopia?

Age-related decline in accommodation due to changes in the lens/ciliary apparatus; reduced elasticity leading to difficulty focusing on near objects.

What are Presbyopia Signs & Symptoms?

Decreased near visual acuity, reduced amplitude of accommodation (< about 5 D), increased lag of accommodation, eye strain and fatigue with near work.

How is Presbyopia corrected?

Convex (plus) lenses such as reading glasses, bifocals, multifocals, progressive lenses.

What is the basic concept of Astigmatism?

Ametropia where the eye’s refractive power is not the same in all meridians, producing two focal lines and blurred vision.

What causes Astigmatic Ametropia?

Index astigmatism (refractive index differs by meridian), curvature astigmatism (different corneal/lens curvatures), and positional astigmatism (lens displaced from optical axis).

How is Astigmatism Corrected?

With cylindrical lenses that have power in only one meridian; treatment depends on type and axis.

What are Common Astigmatism Classifications by Diopters?

Low 0.25–1.00 D; Medium 1.25–3.00 D; High >3.00 D.

What is Anisometropia? (revisited)

A significant interocular difference in refractive error, potentially affecting binocular vision.

What is the Eyelids’ Primary Function?

Protection of the eye and distribution/drainage of tears; blinking spreads the tear film.

What is Ptosis?

Drooping of the upper eyelid; can be congenital or acquired due to injury or aging.

What is Punctum?

A small tear drainage opening on the eyelids near the nose that can become blocked.

What is Conjunctiva?

Bulbar conjunctiva covers the front sclera; palpebral conjunctiva lines the eyelids; they meet at the fornix.

What are the Cornea and Sclera?

The cornea is the transparent front window that refracts light; the sclera is the opaque white outer wall; they merge at the limbus.

What is the Limbus?

The junction where the cornea meets the sclera.

What is the Iris and Pupil?

Iris is the colored diaphragm with a central pupil; pupil size changes with lighting; anisocoria is unequal pupil size.

What is the Crystalline Lens?

The lens behind the iris that changes focus; cataracts occur when the lens becomes cloudy.

What is the Ciliary Muscle?

Muscle around the lens; when it contracts, the lens becomes more convex to increase power for near vision (accommodation).

What is the Anterior Chamber?

The space between the cornea and the iris, filled with aqueous humor.

What is the Posterior Chamber?

The space between the iris and the lens, filled with aqueous humor.

What is the Vitreous Chamber?

Space between the lens and retina filled with vitreous humor; maintains eye shape and is attached to the retina and optic nerve.

What is the Choroid?

The vascular layer between retina and sclera; nourishes inner eye; comprises Haller’s, Sattler’s, choriocapillaris, and Bruch’s membrane.

What is the Retina?

The inner, multi-layered sensory tissue that converts light into neural signals sent to the brain via the optic nerve.

What is the Macula and Fovea?

Macula is the central retina for detailed vision; the fovea is the central pit within the macula that provides the sharpest vision.

What is ARMD?

Age-related Macular Degeneration; degeneration of the macula often with drusen causing loss of central vision.

What is the Optic Nerve’s Role?

Transmits visual information from the retina to the brain; includes the optic cup and optic disc; contains the blind spot.

What is Cup/Disc Ratio (C/D ratio)?

Ratio of the optic cup diameter to the optic disc diameter; normal around 1:3 (≈0.3); used in glaucoma assessment (ISNT rule describes the neuroretinal rim).