Corneal Disorders and Surgical Management - Prof. Sangral, Lecture notes of Mathematics

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notes

Dhaval Patel

MD (AIIMS)

1st Edition

i Ophthalmology PG Exam Notes

CORNEA

Thank you GOD

This manual is collection of the notes I made, found in books or internet while

studying for the Final MD exams for ophthalmology.

I have segregated topics just like book chapters to find them back easily. Though these all

might be far less then other preparation notes available, I am proud of what I have made

and I feel nice to present them to my upcoming ophthalmology friends.

Good luck!

-Dhaval Patel MD [email protected] February 2014

I notes

(Ophthalmology PG Exam Notes)

CORNEA

• Evaluation of the Cornea and External Eye
• DD in Cornea ................................................................................................
• Eye Banking .................................................................................................
• Diseases of the Lid .........................................................................................
• Disorders of Tear Production ............................................................................
• Conjunctival Tumors ......................................................................................
• Conjunctivitis ...............................................................................................
• Developmental Abnormalities of Cornea ..............................................................
• Noninflammatory Ectatic Disorders ....................................................................
• Keratoconus .................................................................................................
• Iridocorneal Endothelial Syndrome ....................................................................
• Corneal and Conjunctival Degenerations .............................................................
• Corneal Dystrophy .........................................................................................
• PUK ...........................................................................................................
• Corneal Infections
• Pterygium..................................................................................................
• Corneal Complications of Intraocular Surgery
• Mechanical Injury
• Chemical Injuries of the Eye
• Keratoplasty
• Keratoprosthesis
• Ocular Surface Transplantation
• Amniotic membrane Transplantation
• Refractive Surgery

Therapeutic Lamellar Keratoplasty Therapeutic Keratoplasty Surgical Management of Superficial Corneal and Conjunctival Disease Phototherapeutic Keratectomy Conjunctival Flaps Iris Reconstruction Surgery Keratoprosthesis Postoperative Management of Keratoprosthesis Ocular Surface Transplantation Limbal Stem Cell Deficiency Amniotic membrane Transplantation Prokera

Refractive Surgery Patient Evaluation and Selection Topographic Analysis Incisional Corneal Surgery Onlays and Inlays Photoablation Collagen Shrinkage C3R All FemtoSecond Sx INTRACOR Intraocular Surgery

Evaluation of the Cornea and External Eye

Examination of the Lids

 History of Patient

 Dermatologic Examination

 Eyelid Position: ectropion and entropion, Floppy Eyelid Syndrome

 Tear Meniscus and Puncta

 Anterior Eyelid: A collarette , which forms in areas of inflammation or hyperkeratinization, is simply mucous debris, Lice, Demodex

 Posterior Eyelid

 Meibomian Gland Expression : normal diameter of each dome is 0.5–0.7 mm , The volume of lipid is increased if any of the lipid domes are 0.8 mm or larger; this finding is sufficient to diagnose seborrheic meibomian gland dysfunction viscosity and opacity of the expressed lipid are important signs

 After instilling lissamine green, rose Bengal or fluorescein onto the ocular surface, a visible line of demarcation, called the Marx line , is often apparent on the lid margin. This line is thought to represent the mucocutaneous junction , and anterior displacement relative to the meibomian gland orifices may correlate with gland dysfunction.

 Meibomian Gland Imagery : The most obvious change seen with transillumination is gland dropout. Dropout is associated with obstructive meibomian gland dysfunction and is not associated with infectious blepharitis, allergic phenomenon, or seborrheic meibomian gland dysfunction.

Tear Film Evaluation

 General Inspection: Alterations in the eyelid structure

 Inferior marginal tear strip : normally about 0.5 mm in width and has a concave upper aspect. If this strip is thin (<0.25mm) or discontinuous, it is evidence of deficient aqueous tear volume.

 Tear Stability :

o The interval between the last complete blink and the appearance of the first random dry spot is the break-up time ( BUT ). Normally 10 – 30 seconds. Values of

 Meibomian Gland Structure and Excreta

o Expression of Meibum

o transillumination of the eyelid

 Tear Clearance Tests

o Dye dilution studies : concentration of the dye is measured over time.

o Fluorescein Clearance Test [FCT]:

o This tear function index (TFI) is the ratio of the value of the Schirmer's test over the tear clearance rate. The use of the TFI in the diagnosis of dry eye disease is reported to demonstrate a specificity of 91% and a sensitivity of 79%.

 Staining of the Ocular Surface

o Fluorescein, which stains damaged epithelial cells, is best visualized on the corneal surface.

o Staining of the conjunctiva is seen when there are disruptions in the protective mucin coating; RB and LG are used.

 Tests of visual function

o tear stability analysis system (TSAS) , serial videokeratographic images are collected each second between blinks.

o functional visual acuity (FVA) device has been developed which measures visual acuity by way of rapid presentation of optotypes.

Corneal Diagnostic Techniques

 Corneal Staining

o Fluorescein and rose Bengal: both dyes can stain living cells, rose Bengal does so more effectively and is intrinsically toxic. healthy preocular tear film will block rose Bengal staining of healthy and damaged cells. Cell degeneration or death increases membrane permeability to both dyes, but rose Bengal diffusion into the stroma is limited. Fluorescein stains BM of epithelial defect, while RB stains dead epithelial cells even without epithelial defect.

o Lissamine green : better tolerated than rose Bengal.

 Pachymetry

o thinnest part of the cornea is usually located about 1.5 mm temporal to the center of the cornea

o Mean thickness is 515 μm in the central cornea.

o cornea with a central thickness greater than the thickness in the midperipheral should be considered suspicious for endothelial dysfunction centrally or thinning in the midperiphery

o If the intraocular pressure is normal, epithelial edema develops when the stroma has swollen about 40%, to a corneal thickness greater than 700 μm.

o corneal striae become visible at 4–8%, folds are seen at 11–12% swelling, and loss of transparency can occur at greater than 20% swelling.

o Techniques for measuring CCT include optical pachymetry, ultrasound pachymetry, confocal microscopy, ultrasound biomicroscopy, optical ray path analysis or scanning slit corneal topography, and optical coherence tomography.

 Aesthesiometry

o cotton-tipped swab

o Cochet-Bonnet aesthesiometer : 6.0 cm -long adjustable nylon monofilament , Measurements are taken by advancing nylon filament smoothly and perpendicularly toward the center of the cornea. Contact is detected by the slightest bend of the nylon; sensitivity is measured as the length of the filament that gives a 50% positive response from a minimum of four stimuli. The normal cutoff is 4.5 cm , and measurements below this are compatible with decreased sensation.

o jet of warm saline

o noncontact air puff technique

o Ocular sensitivity is greatest in the central cornea except in elderly patients, in whom the peripheral cornea is the most sensitive.

Keratometry and Topography

 1619, Father Christopher Scheiner observed that shiny glass spheres of different radii produced reflected images of different sizes

 Ramsden later added a magnification system and also introduced the doubling device

 Types

o flat-target keratoscope : rings of the target are located in the same plane

o Collimating keratoscope : rings in different planes along the interior of a column and in this way are able to maximize the amount of corneal surface that can reflect the target mires

 Limitation

o to produce an obviously distorted image, the cornea must be quite distorted itself

o astigmatism of at least 3 diopters (D) must be present to be detected by traditional keratoscopy.

Videokeratoscopy = Topography

 Klyce in 1984: union of rapid computer analysis and digital video

 Two approaches are in general use currently: the Placido disk or reflection-based topographers, and the scanning slit-based tomographers.

o Placido disk-based topographers :

 vast majority of the older units

 transilluminated cone acting as a modified Placido ring

 Most systems can be divided into ‘near-design’ and ‘distant-design.’

 sensitive to disruptions in the tear film

o Slit scanning tomography

 elevation of each surface can be measured directly with slit beam technology

 The PAR CTS (PAR Technology, New Hartford, NY) was the first ‘topography system’ to produce a true topographic map, using elevation data from the corneal surface.

 Bausch & Lomb Orbscan : Orbscan is a hybrid system – both a topographer and a tomographer – that uses Placido disk technology to display conventional corneal topography. Is is limited in its ability to reliably measure the postoperative posterior cornea , the Oculus Pentacam had greater success in this area.

 Oculus Pentacam uses a scanning slit but with Scheimpflug optics , which increases the depth of focus. In doing so, simultaneous imaging of the cornea, lens, and iris is possible; this permits corneal, anterior chamber, and lens geometry to be imaged and analyzed.

 Zeimer Galilei , also a Scheimpflug imaging device, has similar advantages with regard to image registration and measurement of the posterior corneal surface.

 The main uses of corneal topography

o Preoperative evaluation to rule out certain corneal abnormalities, establish refractive stability, determine whether the patient's corneal shape will allow surgery to be performed safely, and determine whether the surgical outcome is likely to allow acceptable visual performance.

o Operative assessment to determine surgical parameters, plan complicated ‘re-op’ cases, and input data for customized ablations.

o Postoperative evaluation to monitor the surgeon's and laser's performance.

o Aid in the calculation of IOLs for patients who have undergone refractive surgery.

 Presentation Methods

o Color-coded maps : The ‘warmer’ colors represent higher dioptric powers (steeper curvatures), while the ‘cooler’ colors are used to represent the lower dioptric powers (flatter curvatures). Similar color-coded maps can be used to present changes in elevation.

 topographies of fellow eyes tend to be mirror images of each other: enantiomorphs

 The Universal Standard Scale has been adopted by the ANSI standard on corneal topography.

 Axial = sagital Curvature Maps : The cornea has a prolate shape, so power is higher in the center than in the periphery.

 Refractive Power Map : normal cornea will have a higher calculated power peripherally than in the center. This is due to the natural residual spherical aberration of the cornea.

 Instantaneous or Tangential Power Map : not recommended for routine clinical use, extremely useful in the demonstration and measurement of the optical zone size in modern refractive surgery as they emphasize transition zone power changes

 Difference Maps : Progression of keratoconus

 Qualitative Specular Microscopy

o Epithelium:

o Endothelium (miscellaneous bright and dark structures)  Guttae are excrescences of Descemet's membrane. Guttae, however, can also be seen in the far periphery of young individuals. In this case, they are called Hassall-Henle warts.

o Endothelium: morphometry

 Quantitative Specular Microscopy

o endothelial cell density ( ECD ) (measured as cells/mm2), mean cell area (measured as μm2/cell), coefficient of variation ( CV ) (standard deviation of cell areas/mean cell area), and pleomorphism (usually measured as a percentage of 6, <6 or >6- sided cells).

o The variable-frame analysis is more accurate than fixed-frame analysis because only whole cells are counted and it is not necessary to include portions of cells located on the frame boundary.

o Cell density alone is not the most sensitive measure of endothelial health, as the endothelium functions even at low ECDs (under 500 cells/mm2).

o polymegathism (variation in cell area as determined by the CV) and pleomorphism (variation in cell shape as represented by the percentage of hexagonal cells) are a more sensitive measure of the endothelium under stress.

o The corners method

o The Center method (Konan Medical USA)

o the center-flex method

 Clinical Applications

o The ECD at which corneal edema occurs is quite variable, but has been estimated to be between 300 and 700 cells per mm2.

o Difference between two eyes: greater than 280 cells per mm2 is abnormal

o A cornea with a CV greater than 0.40 or the presence of less than 50% hexagonal cells should be considered abnormal and at increased risk for postoperative edema.

o age-related cell loss is approximately 0.5% per year.

o Combined surgery is considered if CCT>600 and Specular <

o The most striking abnormality in keratoconus, however, is elongation of endothelial cells

o FDA-approved Artisan/Verisyse phakic intraocular lens (IOL) has found acceptable mean cell loss rates of 1.8% per year after insertion to correct high myopia.

o Cell loss after PKP: 10% after 2 week, 33% at 3 months, 50 % at 1 year

o Cell loss after EK: 34% cell loss after 6 months, and 38% at 1 year

o vitreous contact mechanically injures the endothelium and interferes with its physiologic function.

Confocal Microscopy

 The optical sectioning ability of confocal microscopy allows images to be obtained from different depths within a thick tissue specimen, thereby eliminating the need for processing and sectioning procedures.

 principle of Lukosz , which states that resolution may be improved at the expense of field of view.

 In 1955, Marvin Minsky developed the first confocal microscope for studying neural networks in the living brain

 Because both condenser and objective lenses had the same focal point, the microscope was termed ‘ confocal .’

 Because the illumination and detection of light through conjugate pinholes occurs in tandem, this microscope was named the tandem scanning confocal microscope (TSCM).

 There are three main confocal imaging systems used clinically:

1. the TSCM
2. the HRT III (a scanning laser system)
3. the Confoscan 4 (a scanning slit system)

High-Resolution Ultrasound

DD in Cornea ................................................................................................

Congenital Corneal Opacities

 3-6 per 100000

 STUMPED classification (Waring)

o Sclerocornea

o Tears in Descemet's membrane: Congenital glaucoma, Birth trauma

o Ulcer: Herpes simplex virus, Bacterial, Neurotropic

o Metabolic (rarely present at birth): Mucopolysaccharidoses, Mucolipidoses, Tyrosinosis

o Posterior corneal defect: Peters’ anomaly, Posterior keratoconus, Staphyloma

o Endothelial dystrophy: Congenital hereditary, Posterior polymorphous corneal dystrophy, Stromal: congenital stromal corneal dystrophy

o Dermoid

 Sclerocornea

o scleralization of the peripheral or the entire part of the cornea

o sporadically, familial or autosomal dominant

o bilateral but commonly asymmetric

o opacification of the cornea is smooth, white, and vascular; it appears to be an extension of the sclera without limbal landmarks

o four groups (Waring et al)

1. Isolated peripheral sclerocornea
2. Sclerocornea plana: <38D, High Hyperopia, Shallow AC, Pseudoptosis
3. Sclerocornea associated with anterior chamber cleavage anomalies: Peter’s

4. Total sclerocornea: the most common form causing congenital corneal opacity,

o Histopathology in sclerocornea

1. Corneal stroma resembles sclera morphologically
2. Precise arrangement of stromal lamellae absent
3. Irregular arrangement of collagen fibers; variable in diameter
4. Collagen fibrils thickened (up to 1500 Å in diameter); resemble scleral fibrils
5. Diameter of collagen fibrils decreases in posterior stroma
6. Changes in posterior cornea may resemble those seen in Peters’ anomaly

o somatic abnormalities such as mental retardation, anomalies of the skin, facies, ears, cerebellum, and testes.

o DD: arcus juvenilis, interstitial keratitis, Peters’ anomaly, and microcornea

 Congenital glaucoma

o epiphora, photophobia, and blepharospasm

o first signs are elevated intraocular pressure, corneal enlargement and clouding, and optic nerve cupping

o increased corneal diameter

o tears in Descemet's membrane can be single or multiple, and appear as elliptical, glassy, parallel ridges on the posterior cornea, either peripherally or across the visual axis. In congenital glaucoma these breaks have a random distribution, most commonly horizontal or concentric to the limbus , in contrast to the oblique and vertical orientation of the breaks in Descemet's membrane seen in birth trauma

 Birth trauma