Contribution of Posterior Corneal Astigmatism to Total Corneal Astigmatism in a Sample of Egyptian Population

Corneal Astigmatism Clinical Trial

Official title:

The Contribution of Posterior Corneal Astigmatism to Total Corneal Astigmatism Using Scheimpflug Analyzer (Pentacam ) in a Sample of Egyptian Population

Clinical Trial Details — Status: Recruiting

Administrative data

• NCT number: NCT04393740
• Other study ID #: Ms-184-2019
• Status: Recruiting
• Start date: April 15, 2020
• Est. completion date: August 15, 2020

Study information

• Verified date: May 2020
• Source: Cairo University
• Contact: alaa mo badawy, Msc
• Phone: 01008858267
• Email: alaabadawy93[@]gmail.com
• Is FDA regulated: No
• Study type: Observational

Clinical Trial Summary

The magnitude of posterior corneal astigmatism was considered negligible due to the smaller difference in the refractive index between the cornea and the aqueous .

though ,neglecting the posterior corneal astigmatism lead to errors during calculation of the toric iols (over or under estimation ) .

so we aim to determine the percentage of contribution of posterior corneal astigmatism to total corneal astigmatism in a sample of Egyptian population using scheimpflug imaging (Pentacam ).

Description:

Astigmatism is a common vision condition that causes blurred vision. Astigmatism is an error of refraction in which incident parallel rays can't be focused to a single point .It could be corneal or lenticular astigmatism or both . Regarding Corneal astigmatism it is due to difference in the corneal curvature in the different meridian of both the anterior and posterior surface .

The are 2 methods of studing corneal curvature :

• Corneal topography which depend on placcido disc to study anterior corneal surface .

• Corneal tomography is more precise in detecting anterior and posterior corneal curvature depending on Scheimpflug principle which uses a rotating Scheimpflug camera .

Pentacam is a device which depend on Scheimpflug technique .

The importance of studing the posterior corneal curvature includes :

• The posterior corneal curvature is a more sensitive indicator of early keratoconus detection especially posterior corneal elevation.

Previously, The change in the posterior corneal surface plays a more subtle role than the anterior corneal surface in optical performance because of the smaller difference in refractive indices between the cornea and aqueous, and it has been thought that the magnitude of PCA in the normal population is clinically negligible.

Posterior corneal astigmatism (PCA) is important for better predictability of toric intraocular lens calculation to avoid under- or overestimation of toricity in intraocular lens (IOL) power calculations.

But recently it has been demonstrated how neglecting PCA will lead to overcorrection of astigmatism in eyes with with-the-rule astigmatism (WTR) and undercorrection in eyes with against-the-rule astigmatism (ATR).(3) In our study we aim to Determine the contribution of posterior corneal astigmatism to total corneal astigmatism and the error in estimating total corneal astigmatism from anterior corneal measurements only using Scheimpflug analyzer (Pentacam ).

Our patients will undergo Scheimpflug imaging using pentacam .

From the corneal parameters displayed in pentacam we can calculate :

• Anterior corneal astigmatism by substracting Ksteep -Kflat on the front surface

• Posterior corneal astigmatism by substracting Ksteep-Kflat on the back surface.

• Total corneal astigmatism is calculated by addition of anterior and posterior corneal astigmatism using vector analysis by using ASSORT vector calculator.*

• The percentage of contribution of posterior corneal astigmatism to magnitude of Total corneal astigmatism is then calculated .

ASSORT vector calculator:

Is a total planning and outcomes analysis software for astigmatism using Alpins method ,cheltman ,Victoria ,Australia .

Recruitment information / eligibility

• Status: Recruiting
• Enrollment: 356
• Est. completion date: August 15, 2020
• Est. primary completion date: July 15, 2020
• Accepts healthy volunteers: Accepts Healthy Volunteers
• Gender: All
• Age group: 18 Years to 45 Years

Eligibility

Inclusion Criteria:

1. Patients with corneal astigmatism(±0.5D up tp ±4 D )

2. Age (18-45 years )

3. Refractive error (myopia up to -8D)

4. Hyperopia up to +4

5. Patients who have clear cornea .

6. Good quality Scheimpflug analyzer scans.

Exclusion Criteria:

1. Patients who have any corneal opacity .

2. Patients who underwent any Previous corneal surgery .

3. Patients who have Co existing corneal pathology.

4. Glaucomatus patients.

5. Patients with any Concomitant ocular disease .

6. Patients with History of previous ocular trauma .

Related Conditions & MeSH terms

• Astigmatism
• Corneal Astigmatism

Intervention

Diagnostic Test:
• scheimpflug imaging using pentacam
corneal tomography imaging using pentacam device (based on Scheimpflug principle )

Locations

Country	Name	City	State
Egypt	kasr El Aini medical school	Cairo

Sponsors (1)

Lead Sponsor	Collaborator
Cairo University

Country where clinical trial is conducted

Egypt, 

References & Publications (2)

Ferreira TB, Ribeiro P, Ribeiro FJ, O'Neill JG. Comparison of Methodologies Using Estimated or Measured Values of Total Corneal Astigmatism for Toric Intraocular Lens Power Calculation. J Refract Surg. 2017 Dec 1;33(12):794-800. doi: 10.3928/1081597X-20171004-03. — View Citation

Rydström E, Westin O, Koskela T, Behndig A. Posterior corneal astigmatism in refractive lens exchange surgery. Acta Ophthalmol. 2016 May;94(3):295-300. doi: 10.1111/aos.12965. Epub 2016 Jan 30. — View Citation

Outcome

Type	Measure	Description	Time frame	Safety issue
Primary	contribution of posterior corneal astigmatism to magnitude of total corneal astigmatism	to detect the contribution of posterior corneal astigmatism to total corneal astigmatism to avoid errors during calculation of toric Intra ocular lenses	3 months