How can ordinary people quickly understand corneal topography?

Friends often ask if they can help with corneal topography reports...

Why is the picture colorful?

Why are the shapes different?

It is better to teach a man to fish than to give him a fish. Today, I will teach you how to quickly understand corneal topography!

Wei Jing, Director of Chengdu Yinghua Eye Hospital<<

Corneal topography can accurately measure and analyze the curvature and refractive power of any point on the anterior surface of the cornea. It is a systematic and comprehensive quantitative analysis method for studying corneal morphology.

At the same time, corneal topography can detect diseases that were previously impossible to diagnose with conventional examinations. Its clinical application is mainly reflected in the following four aspects:

• Preoperative screening for refractive surgery
• Contact lens fitting
• Diagnosing Keratoconus
• Diagnosis of other anterior segment diseases

The report below is called the Refractive Four-Chart. The OD in the upper right corner represents the right eye, and the OS represents the left eye.

Look at the color

The computer digitizes the stored corneal image, analyzes it, and displays the result in color. The change in color represents the change in diopter .

The average Chinese corneal steepness is shown as → green

As the steepness increases, it gradually turns yellow, orange, and red.

As the steepness decreases, it gradually appears as → light blue, dark blue

Warm colors represent parts with strong refractive power, indicating that the cornea is steep;

Cold colors represent the part with weak refractive power and flat cornea.

Look at the shape

The main thing to look at is whether there are "C"-shaped or central island-shaped changes in the quadruple diagram.

If the changes are C-shaped, it means that the next step may be to change to an island shape. In this case, it is usually necessary to wait 3-6 months before rechecking the topography or surgery is not recommended;

If it is a central island, it is a typical keratoconus image, and myopia surgery is not recommended;

If there are no C-shaped or central island-shaped changes in the keratoconus demonstration picture, it can be basically determined that the cornea is normal.

Collection quality specifications

The box displays OK: All data are correct;

Yellow box: There is some data loss or error;

Red in the box: data is unreliable;

Summary: The collection quality specifications need to be looked at first to determine whether the collected data is reliable.

Corneal curvature

Km＜39D , indicating that the cornea is relatively flat, and it is likely to be a flat cornea;
Km＞46D , indicating that the cornea is steeper and there may be high astigmatism or keratoconus problems;

Summary: The normal range of corneal curvature is 39D-46D, and the average value is around 43D.

Corneal thickness

The average thickness of human cornea is 500-550um

Summary: When the corneal thickness is less than 480um, it is best not to undergo laser surgery.

pupil

The normal value of the pupil center is X-axis <0.2, otherwise the all-femtosecond myopia surgery cannot be performed.

01 Accurately analyze corneal astigmatism

Astigmatism comes from changes in the cornea, lens, and various refractive indices.

Low-degree astigmatism may come from different anatomical factors, while high-degree astigmatism mainly comes from abnormal corneal curvature.

02 Screening for keratoconus

Keratoconus is a congenital corneal developmental abnormality in which the central part of the cornea progressively thins and protrudes forward in a cone-like shape due to non-inflammatory conditions.

A disease in which the local curvature of the cornea becomes higher and is out of harmony with the periphery, resulting in local corneal protrusion.

03 Significance for refractive surgery

Corneal topography can determine corneal astigmatism and its axis, and understand the size of the refractive power.

Analyzing the corneal surface morphology in special cases can help determine the surgical area and amount of surgery.

Regarding corneal topography, this is all you need to know. For a more in-depth interpretation, it is best to ask a professional doctor or optometrist.