User Guide for HOYA Toric Calculator

The HOYA Toric Calculator (HTC) is a resource for the treating physician to aid in proper intraocular lens (IOL) cylinder power selection for cataract patients with corneal astigmatism. The HTC requires the User to input patient keratometry and biometric data and planned surgery information that is part of a pre-operative work up prior to toric IOL (TIOL) implantation. The HTC will suggest several HOYA TIOLs from which the surgeon may choose to treat a patient’s refractive cylinder resulting from corneal astigmatism. The HTC will also provide suggested intra-operative axial placement of the IOL that is to minimize postoperative astigmatism.

This 4 revision of the calculator provides an option that accounts for induced astigmatism from the posterior surface of the cornea. The calculator allows the User to apply the Abulafia - Koch Regression formula i. This regression, which is based on clinical results, uses standard keratometry measurements of the anterior surface of the cornea and estimates the added astigmatic effect of the posterior cornea to produce an overall net astigmatism of the cornea. The Abulafia - Koch Regression, applied to a clinical patient cohort, has been shown to improve predictability of TIOL refractive outcomes. The regression was developed using eyes considered to be inside normal range of eye biometry with no prior corneal refractive surgery. The results of the regression may not be applicable to individual eyes with corneal abnormality (e.g. Keratoconus, post Penetrating Keratoplasty, post refractive surgery). Only anterior corneal curvatures values are appropriate for use of the Abulafia Koch Regression.

Users of the calculator also have the option to enter keratometry values that represent the total corneal power. Many anterior segment imaging and biometry diagnostic tools, such as Scheimpflug and optical coherence tomography (OCT) imagers, can measure curvature values for both the anterior and posterior surfaces of the cornea. These instruments produce keratometry values representative of the total cornea. These total corneal power values can be entered as keratometry input and the calculator will provide astigmatism results representative of the total cornea. If the User enters total corneal power values the Abulafia - Koch Regression should be turned OFF.

This 4 revision of the calculator also provides optional input of axial length (AL) that together with keratometry values, Spherical Equivalent IOL Power and the Holladay 1 formula ii will estimate position of the effective lens position (ELP) of the TIOL and adjust the TIOL cylinder power on corneal plane. iii The use of the Holladay 1 formula, includes Wong-Koch AL adjustments for eyes with AL > 25.0 mm. iv

Warnings and Precautions
  1. The recommended lenses and axis of placement are to be informative for the User and are not intended to replace the medical expertise or judgment of the surgeon or operator.
  2. The accuracy of the TIOL options presented is dependent on precise measurements of the patient's eye and exact entry into the calculator. The User should verify proper data entry before final IOL selection.
  3. The Abulafia - Koch Regression results may not be applicable to individual eyes with corneal abnormality (e.g. Keratoconus, post Penetrating Keratoplasty, post refractive surgery).
  4. Only anterior corneal curvatures values are appropriate for use of the Abulafia Koch Regression.
Locating the HOYA Calculator

The HTC revision 4 is openly accessible on the internet for all Users. The calculator can be found at This calculator is compatible for use with internet web browsers including Internet Explorer (ver. 11 or newer), Google Chrome (54 or newer), Firefox (ver. 43 or newer), Safari (ver. 9.1 or newer) and Microsoft Edge (ver. 38.14393 or newer).

User select language and country

Upon entering the website with a compatible internet browser, the User will be led to a page that will prompt the User to select a language for use and to select a region and country. The choice of country will restrict the TIOL models offered to those available in the specified country. User should click the “Submit” button to move forward.

Terms and Conditions

After reading the Terms and Conditions, the User must click the “I Accept” button to indicate acceptance and advance to enter patient information. User must accept Terms and Conditions the first time using the website. The User's acceptance will be remembered by the browser’s cookies for subsequent visits within 30 days.

Patient data input

After accepting the Terms and Conditions, the data input page is shown. Using the tab key to advance to the next field, a complete set of data must be entered by the User as prompted by the calculator for the following entries:

Patient and Surgeon Information

The User must enter the following required information:

The User may also choose to enter the following optional information [Optional]:

All information entered will be shown in printed output.

Calculator Preferences

Several fields are shown that allow the User to customize the calculator for their preferred method of use. The User's preferences will be remembered in the browser’s cookies and will be applied the User's next session.

IOL selection

Model Number: Based on the User's Country the calculator will display in the pull-down menu only HOYA TIOLs available in that country. The User must select one of the available TIOL models. If only one TIOL is available, that model will display as the default selection. If multiple TIOLs are available the User’s selection of a preferred model will be recalled in the browser’s cookies.

HOYA TIOL Models* Product Description
AF-1 Monofocal Toric Family : 351 / 355 Monofocal aspheric, one-piece toric, yellow, preloaded in screw type
Vivinex Monofocal Toric Family : XY1A / XY1A-SP Monofocal aspheric, one-piece one-material toric, yellow, preloaded in screw type or screw-push type injector
Vivinex Gemetric Multifocal Toric Family : XY1-GT / XY1-GPT Multifocal aspheric, one-piece one-material toric, yellow, preloaded in screw-push type injector

For more product information please contact your local sales representative.

* Some intraocular lens models described in the table may not be approved for sale in your country. Please check with the HOYA distributor in your country for a full list of IOL models available in your country.

Spherical Equivalent IOL Power (D): User must select from the pull-down tab the appropriate value of the spherical power of the lens which is determined by User’s method of choice and preferred formula for the particular eye.

Eye Selection

The User must select Right Eye-OD or Left Eye-OS for the toric calculations. This selection will display in all images and print out for the calculation results.

Eye View(Upper-right corner of the graphic image of the eye)

The user can select an orientation of the image of the eye for print using the pull down tab on the upper right of the eye image. The orientation of the eye image can be printed from the following three options:

Keratometry Data Entry

All numeric entries that are decimal values may be entered using either a dot (.) or a comma (,) to serve as the decimal point. For example, 1.05 may be entered or as 1,05 and will be recognized by the calculator as the same value.

Surgical Information

Adjust ELP and Cylinder Power on Corneal Plane [Optional]

A measured value of Axial Length is used to estimate the Effective Lens Position (ELP) of the IOL and will adjust the TIOL cylinder power on the corneal plane. The value should be in a range from 18.0 to 30.0 mm. If Axial Length is not entered the calculator will use a fixed cylinder value power on the corneal plane that is based on average pseudophakic human eye geometry with the values shown in the Table below.

Calculation Result and IOL Selection

After the complete data set is entered the User should click the CALCULATE button. The graphic image of the eye will update to show the calculated values and display the steep and flat axes of the cornea with the incision and IOL placement. The calculator will also generate three toric lens options of different cylinder power for the User to consider. The astigmatic correction will be calculated for all toric lens powers and for a non toric lens. If the optional axial length data entry is not input, the calculation for fixed TIOL cylinder power on the corneal plane will be applied according to the following properties:

Lens Type Model IOL Cylinder Power Cylinder Power at the Corneal Plane*
AF-1 Monofocal Toric Family Vivinex Monofocal Toric Family Vivinex Gemetric Multifocal Toric Family
Non-toric IOL --- 0.00 D 0.00 D ** 0.00 D *** 0.00 D ***
Toric IOL T2 1.00 D --- 0.69 D 0.69 D
Toric IOL T3 1.50 D 1.03 D 1.04 D 1.04 D
Toric IOL T4 2.25 D 1.55 D 1.56 D 1.56 D
Toric IOL T5 3.00 D 2.06 D 2.08 D 2.08 D
Toric IOL T6 3.75 D 2.58 D 2.60 D 2.60 D
Toric IOL T7 4.50 D 3.09 D 3.12 D ---
Toric IOL T8 5.25 D 3.61 D 3.64 D ---
Toric IOL T9 6.00 D 4.12 D 4.17 D ---
* Based on an average pseudophakic human eye. ** Equivalent models with no cylinder power (non-toric IOL) of AF-1 Monofocal Toric IOL are AF-1 Monofocal IOL (model 251 and 255) respectively. *** Equivalent models with no cylinder power (non-toric IOL) of Vivinex Monofocal Toric IOL are Vivinex Monofocal IOL (model XY1 and XY1-SP) respectively. **** Equivalent models with no cylinder power (non-toric IOL) of Vivinex Gemetric Multifocal Toric IOL are Vivinex Gemetric Multifocal IOL (model XY1-G or XY1-GP) respectively.

The calculator will display up to three lens options depending on the input information. The TIOL options will be listed from left to right as under correcting astigmatism to over correcting astigmatism. The lens selection shown as “Option 2” in the center will be the TIOL with cylinder power that will minimize the patient’s astigmatism without over-correcting the cylinder and flipping the astigmatic axis 90°. Option 1, on the left, is the TIOL that is the next available cylinder power lower than Option 2. Option 3 on the right is the TIOL that is the next available cylinder power higher than Option 2; this TIOL might indicate residual astigmatism close to zero but will result in flipping the axis of astigmatism 90°. These lens offerings are informative for the User and the selection of one of these lenses is solely based on the medical expertise of the surgical team to provide the best correction for their patient.

The HTC will also inform the User of the recommended axis for TIOL placement and will include an image of the eye with the incision location, steep and flat corneal axes, and the axis of placement for the TIOL.

The User must select one of the TIOL options lenses offered or may re-enter any of the values or data entry options and again click the CALCULATE button to recalculate. Once a TIOL option is selected that selection will be highlighted in yellow. If Option 3 is selected a warning will appear that says, “Your selection has the potential to rotate the patient’s axis of astigmatism 90°. Do you want to proceed?” The User must select yes to proceed or no to return to the data entry page. A “Clear Fields” button is available in the middle of the page to restart data entry.

Printing and Exporting Calculation Result

Following three options are available for printing and exporting the calculation results.

New calculation

If the User wishes to start a TIOL selection for a new patient, New Calculation will clear all fields including patient identification and allow a new entry.

Help Guidance for HOYA Toric Calculator Compatibility

The user’s individual computer, network settings, choice of web browser and software settings may affect optimum performance of the toric calculator. These variables may prevent the site from providing results or may result in less than optimum printed output. Please use the guidance below to investigate and correct likely issues.

  1. JavaScript and Cookies must be enabled.
    1. JavaScript settings can usually be found in your browser toolbar under Tools/Options/Content section
    2. Cookies settings can usually be found in your browser toolbar under Tools/Options/Privacy
    3. Additional plug-in or programs could be preventing JavaScript or cookies from working properly.
  2. Printer settings
    1. If your printer does not print immediately please allow 4-5 seconds for the printer driver to open
    2. If your printer driver still does not come up:
      1. Look for a browser indicator or yellow bar at the top or bottom of the page that will enable printing, set it to always allow printing from this website.
      2. Active Scripting – If the computer is on a work network the security setting on your computer or network may not allow active scripting and block the printer driver. Please work with your IT department to enable active scripting for this website.
    3. If your printout is not optimized to fill a single page, printer settings can usually be found in your browser toolbar under File/Page Setup.
      1. Scale to fit the page – Enabling Shrink to Fit should optimize a single page print-out. If that doesn’t work, then use the print scale to optimize the print-out.
      2. Header and footer - Displaying web page titles and URLs in the header or footer of the printout may be default settings of your browser. These can be turned on or off to format the printout as desired.
  3. Browser Backward / Forward buttons – Please use the active buttons on the website or the progress bar at the top of the pages where ever possible to navigate through the steps of entering data, going forward or backward to change or update information. The action of the browser’s back button is not controlled by the web site and may be handled differently depending on the browser used.
  4. Contact HOYA – All entries on the Contact HOYA page should be made using Latin (English) characters, as other characters cannot be processed. Other character sets, like Japanese or Arabic, used in the name and email fields will not be recognizable to the HOYA representative receiving the message.

Manufacturer Information:
HOYA Medical Singapore Pte. Ltd.
455A Jalan Ahmad Ibrahim
Singapore 639939
Authorized Representative in the European Community:
HOYA Surgical Optics GmbH
De-Saint-Exupéry-Strasse 10,
60549 Frankfurt am Main, Germany
Revision date: 1 Aug 2020


  1. Abulafia A et al, “New regression formula for toric intraocular lens calculations,” J Cataract Refract Surg 2016; 42(5):663-671
  2. Holladay JT et al, “A three-part system for refining intraocular lens power calculations,” J Cataract Refract Surg 1988; 14(1):17–24
  3. Fam HB and Lim KL, “Meridional analysis for calculating the expected spherocylindrical refraction in eyes with toric intraocular lenses,” J Cataract Refract Surg 2007; 33(12):2072-2076
  4. Wang L et al, “Optimizing intraocular lens power calculations in eyes with axial lengths above 25.0 mm,” J Cataract Refract Surg 2011; 37(11):2018–2027