What do Placido disc topographers directly measure?

What do Placido disc topographers directly measure?

Placido Disc Topography After projecting a concentric annular light source onto the corneal surface, placido disc reflection systems capture the reflected light so their software can measure curvature, irregularities, foreign bodies, tear film nuances and other characteristics of the anterior cornea.

What is Placido disc examination?

assess shape of cornea. A keratoscope, sometimes known as Placido’s disk, is an ophthalmic instrument used to assess the shape of the anterior surface of the cornea. A series of concentric rings is projected onto the cornea and their reflection viewed by the examiner through a small hole in the centre of the disk.

How do you read keratoconus?

Central Keratometry (K Central). This is the average value of corneal power for the rings with diameters of 2, 3 and 4 mm. Values below 47.2 D are considered normal, while values between 47.2 and 48.7 D are considered probable keratoconus. Values above 48.7 D are clinical keratoconus [14, 74].

How do I read a pentacam report?

A value between 0 to -1 is considered normal and indicates a prolate shape (steep centre and flat periphery). A value >0 indicates an oblate cornea (flat centre and steep periphery) and a value < -1 indicates a hyperprolate cornea as seen in corneal ectasia.

What is considered irregular astigmatism?

Irregular Astigmatism In irregular astigmatisms, the principal meridians are separated by any angle other than 90°, i.e., they are not perpendicular to each other. In this type, the curvature at each meridian is not uniform but changes from one point to another across the entrance of the pupil.

How do you do a Placido disc exam?

Slit-scanning Evaluation Topography The slit-scanning elevation topography combines a projection of the slit of light (same principle as a slit lamp biomicroscope) with a reflection of a placido-disc (keratoscopy principle), to obtain anterior and posterior corneal curvature measurements.

What is considered mild keratoconus?

The mildest form of keratoconus is called Forme Fruste Keratoconus. Forme Fruste Keratoconus is sub-clinical and symptom free. Diagnosing Forme Fruste Keratoconus is really only possible through corneal topography.

What is the normal astigmatism?

Regular astigmatism Each meridian in the regular astigmatic eye has a uniform curvature at every point across the entrance of the pupil. This is the most common type of astigmatism in which the symptoms included are blurry vision, headaches, and light sensitivity, to name a few.

Is irregular astigmatism a medical condition?

Certain types of surgery or eye injuries that cause scarring of the cornea may cause astigmatism. Keratoconus is a degenerative disorder of the eye where the cornea gradually thins and changes to a more conical shape. This can cause a condition known as irregular astigmatism.

What is Placido’s disc?

Placido’s disc was a major advancement in the late 19th century. Placido disc has stood the test of time and the current placido based topographers work on the same principle of assessing the reflection of a concentric set of black and white rings from the convex anterior surface of the cornea.

How do topographers use Placido disc technology?

Placido disc technology The original style topographers use Placido disc technology. Circular rings are projected onto the corneal surface, and a camera takes pictures of the rings to determine how steep or flat each area is.

What is the difference between regular and irregular astigmatism?

Regular astigmatism results in mires that appear ovoid (Figure 2C). If irregular astigmatism is present, this may be seen as an irregularly distorted reflection of the mires (Figure 2D). Placido disc evaluation can also be used to guide suture removal following penetrating keratoplasty.

How many diopters of astigmatism do Zeiss maps show?

Zeiss Atlas Report. The tangential and axial curvature maps both show with-the-rule corneal astigmatism with more plus power in the vertical meridian. Specifically, the steepest meridian is at 083 degrees, and there are 2.88 diopters of astigmatism.