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Confocal Microscopy

Key Concepts Confocal microscopy provides high-resolution images of all corneal cell layers in vivo. Confocal microscopy through focusing can be used for three-dimensional assessment of temporal changes in epithelial, stromal, and corneal thickness, nerve regeneration, cell density, and haze estimation after surgery, injury, infection, or disease. Ultrafast, laser-based nonlinear optical imaging of second harmonic generated (SHG) signals from collagen provide an important emerging technology for evaluating the…

Specular Microscopy

Key Concepts Specular microscopy displays light that is reflected in a “mirror-like” fashion off the tissue from the incident light. Specular microscopy’s primary use is in the imaging of corneal endothelial cells, whereas confocal microscopy has replaced it for epithelial and stromal imaging. Endothelial cell density, mean cell area, polymegethism or coefficient of variation, and pleomorphism or percent hexagonality are useful measures. Quantitative and morphologic analyses…

Corneal Shape Analysis and Biomechanical Assessment

Key Concepts Advances in corneal imaging were boosted by the demands of refractive surgery, such as the diagnosis and characterization of ectasia susceptibility. Enhanced refractive surgery screening and planning must go beyond corneal topography and single point ultrasound pachymetry. The diagnosis of mild keratoconus should consider tomographic data, such as posterior elevation and thickness profile (pachymetric data from the thinnest point to the limbus). The diagnosis…

Keratometry and Topography

Key Concepts The growth of keratorefractive surgery has stimulated development in corneal topography. The present-day videokeratoscope, or corneal topographer, evolved from the keratometer. Modern corneal topographers use several different approaches, including Placido disk and grid-style reflections, slit scanning tomography, Scheimpflug optics, and interferometry/optical coherence tomography. Topographic and tomographic devices can display axial or tangential curvature, refractive power, elevation, and pachymetry. Quantitative data can be used to…

Molecular Genetics of Corneal Disease

Key Concepts Genes represent the fundamental units of heredity. Identification of disease-causing genetic variants provides insight into pathogenesis of corneal disorders. Population-based and family-based studies allow researchers to identify disease-associated genetic variants. Genetic discoveries refine the classification of diseases historically defined by clinical phenotype. Altered gene regulation may contribute to corneal disease. Review of Genetics and Human Disease Genes are the fundamental units of heredity. At…

Practical Ophthalmic Microbiology for the Detection of Corneal Pathogens

Key Concepts Since specific ophthalmic microbiology testing is not available at all laboratories, ophthalmologists need to locate microbiology testing for their practices. Microbiology testing must be validated for ocular specimens. Laboratories, in general, are oriented to systemic treatment and may not provide pertinent antibiotic susceptibility testing for topically treating infectious keratitis. Definitive methods to detect bacteria, fungus, virus, chlamydia, and Acanthamoeba are available to the ophthalmologist.…

Tear Film and Corneal Diagnostic Techniques

Key Concepts Dry eye disease (DED) is an umbrella term comprising a variety of clinical manifestations with differing underlying pathophysiologies. In patients presenting with DED, a comprehensive, systematic examination is needed; this should include medical history, symptom assessment, ocular surface evaluation, and vital dye staining. Point-of-care tests and imaging technologies complement the clinical examination and help to subtype DED, stratify severity, and tailor treatment. Available point-of-care…

Slit Lamp Examination and Photography

Key Concepts Isolation of the layer or entity to be viewed is the key to slit lamp biomicroscopy. Techniques of biomicroscopic examination include diffuse illumination, broad beam illumination, optical section, indirect illumination, red reflex illumination, specular reflection, and sclerotic scatter. Slit lamp photography employs the same modes of illumination with modifications (such as the fill light) necessary for accurate photographic documentation. “On August 3, 1911, Alvar…

Examination of the Lids

Key Concepts An anatomically and physiologically normal eyelid is vital in maintaining the health of the eye. Observing unconscious behaviors while collecting the patient’s history may provide valuable insight into underlying disorders. Examination should begin under ambient lighting prior to the administration of drops so as to reduce artifact. Examination of the tear film yields valuable information in the diagnosis and treatment of dry eye. Examination…

A Matrix of Pathologic Responses in the Cornea

Key Concepts Four regions of the cornea are: (1) epithelium, (2) subepithelial zone (epithelial basement membrane, Bowman layer, superficial stroma), (3) stroma, and (4) endothelium and Descemet membrane. Six corneal responses are: (1) defects and their repair, (2) fibrosis and vascularization, (3) edema and cysts, (4) inflammation and immune responses, (5) deposits, and (6) proliferation. There are two distinct types of immune response to antigens: (1)…

Eyelids and the Corneal Surface

Key Concepts The eyelids function to cover, cleanse, and lubricate the eye. The eyelid skin is the thinnest in the body and allows for unrestricted movement. The tarsal plates provide structural stability to the eyelids. The orbicularis oculi is important for eyelid closure and the involuntary blink reflex. The conjunctiva, meibomian glands, and lacrimal glands produce secretions that make up the tear film. Introduction An understanding…

Tear Film

Key Concepts Tear film stability is essential to maintaining ocular surface health. Lipids, mucins, and aqueous are the major components. There has been a shift from a strict three-layer model to understanding the tear film as a single dynamic functional unit. With technologic innovation, evaluation of the tear film has become more precise, allowing for better understanding of normal and diseased ocular surfaces both in clinical…

The Conjunctiva : Anatomy and Physiology

Key Concepts The conjunctival and limbal epithelia are derived from surface ectoderm. The mucocutaneous junction at the lid margins is the junction between hydrophobic (unwettable) epidermis and hydrophilic (wettable) conjunctiva. The corneoscleral limbus is a unique stem cell niche microenvironment that supports a population of pluripotent limbal stem cells. Injury to the limbus and loss of limbal stem cells result in conjunctivalization of the cornea. Conjunctival…

Cornea and Sclera: Anatomy and Physiology

Key Concepts The principal physiologic role of the cornea is to allow external light to enter the eye and to contribute to its focusing on the retina. Thus transparency and refractive power are essential for this function. The cornea consists of the epithelium, Bowman layer, stroma, Descemet membrane, and endothelium. The functions of the corneal epithelium are regulated by various biologically active agents such as growth…