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

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

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 ).

Study Overview

• Status: Unknown
• Conditions: Corneal Astigmatism
• Intervention / Treatment: Diagnostic test: scheimpflug imaging using pentacam

Detailed 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 .

• Study Type: Observational
• Enrollment (Anticipated): 356

Contacts and Locations

Study Locations

• Egypt
  • Cairo, Egypt
    • Recruiting
    • kasr El Aini medical school
    • Contact: sarah A Azzam, MD; Phone Number: +20 01227425601; Email: Sarahazzam@ymail.com
    • Contact: alaa MO badawy, Msc; Phone Number: +20 0100858267; Email: alaabadawy93@gmail.com

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years to 45 years (Adult)
• Accepts Healthy Volunteers: No
• Genders Eligible for Study: All

• Sampling Method: Non-Probability Sample

Study Population

candidates presenting for refractive surgery .

Description

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 .

Study Plan

How is the study designed?

Design Details

• Observational Models: Cohort
• Time Perspectives: Cross-Sectional

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
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

Collaborators and Investigators

• Sponsor: Cairo University

Publications and helpful links

General Publications

• 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.
• Rydstrom 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.

Study record dates

Study Major Dates

• Study Start (Actual): April 15, 2020
• Primary Completion (Anticipated): July 15, 2020
• Study Completion (Anticipated): August 15, 2020

Study Registration Dates

• First Submitted: May 14, 2020
• First Submitted That Met QC Criteria: May 18, 2020
• First Posted (Actual): May 19, 2020

Study Record Updates

• Last Update Posted (Actual): May 19, 2020
• Last Update Submitted That Met QC Criteria: May 18, 2020
• Last Verified: May 1, 2020

More Information

Terms related to this study

• Additional Relevant MeSH Terms: Eye Diseases; Refractive Errors; Astigmatism
• Other Study ID Numbers: Ms-184-2019

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: Yes
• IPD Plan Description: we would share our protocol and results through publishing our research
• IPD Sharing Time Frame: the data would be available within 3 months and would be available for 6 months
• IPD Sharing Supporting Information Type: Study Protocol

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: Yes
• product manufactured in and exported from the U.S.: No