Fitting mixed astigmatism with Orthokeratology lenses

Pre Treatment Data

History

Mr JS a 57-year-old accountant presented to the practice interested in contact lenses. He noted I had fitted his brother and sister in law with orthokeratology lenses and was interested to find out if he was a candidate. He noted his previous optometrists had told him he wasn’t a candidate for contact lenses due to his astigmatism and presbyopia.

Following a thorough assessment of his refraction, ocular surface, dominance, and corneal topography a frank and honest discussion was had with Mr JS regarding of the likelihood of success, the technical nature and challenge of fitting mixed astigmatism with orthokeratology, and the challenge and limitations of managing presbyopia. Regardless of the challenges associated with his case, Mr JS was keen to proceed.

It was decided that we would try to achieve the best distance vision first, and then fit the right eye for best near vision in a monovision set up.

K Readings (pre-treatment only)

Baseline Corneal Topography

Axial Power

Elevation

Corneal height analysis - Flat meridian

Corneal height analysis - Steep meridian

Corneal Topography Assessment

Concerns

  • 2.98D of WTR Corneal Astigmatism
  • Limbus to limbus astigmatism characterised by a 0.30 difference in eccentricity between the flat (0.50e) and steep (0.20e) meridian.
  • Weighted average height at the 8.00 mm chord Flat meridian (1.2 degrees) 1051.5µm, Steep (91.2 degrees) 1134.4µm. Difference 82.9µm.
  • In order to correct distance refraction with orthokeratology, I need to create 1.00D of corneal steepening in the horizontal meridian and 2.50D of corneal flattening in the vertical meridian.
  • Might not work...
  • May require many remakes to fit the corneal toricity and correct the astigmatism.

Assessment

  • Large (11.70 mm) HVID
  • Regular WTR corneal toricity
  • Centred corneal apex

Plan

  • Custom design the lens using EyeSpace contact lens design software.
  • Aim for best distance vision with the first lens. Will aim for more plus correction for best near vision after achieving best distance vision.

Other: why is this case interesting or complex?**

Mixed Astigmatism and adjustment for overcorrection of the WTR astigmatism with the initial lens.

Lens 1

Design Parameters

Description of lens design:

Zone 1 (Back Optic Zone):

Does not fit the cornea, rather is responsible for the amount of refractive change. BOZR = SimK + Spec Rx + Jessen Factor. Eg. 42.00 + -3.00 + -0.75 = 38.25D = 8.823 mm

Zone 2 (Venturi Zone):

Fitted slightly flatter than the cornea to increase the negative suction effect (Flat meridian only)

Zone 3 (Z-Zone):

Commonly referred to as a reverse curve, controls the overall depth and the clearance of the edge of the back optic zone.

Zone 4: (Blend Zone):

Reduces the change in angle between Zone 3 and Zone 5. Reduces insult to the corneal epithelium, while maximising the migration of epithelial cells in the paracentral cornea.

Zone 5: (Alignment Zone):

Responsible for the lens-corneal bearing and centration on the eye. The lens-corneal angle of bearing is the key concept to achieving perfect centration. The lens-corneal angle of bearing can be best visualised and assessed by the cross-section tear layer profile of the alignment zone. The ideal fit is one where the lens-corneal angle is slightly negative (tear layer thickness reducing from inner to the outer aspect of the alignment zone) in the horizontal meridian and slightly positive in the vertical meridian to enable vertical movement of the lens with blink.

Zone 6: (Edge lift):

The edge lift aids the centration and movement of the lens on blink. It also prevents the lens from binding on the eye and causing corneal and limbal insult at the edge of the lens. If possible the desired edge lift is 75 microns, however, should never be less than 50 microns or greater than 100.

Lens Diameter:

The lens diameter should be 93-97% of the HVID. However, the lens should never overlap the limbus. Special attention in assessing the vertical size of the lens in comparison with the vertical diameter of the cornea, as the VVID may be much smaller than the HVID especially in high toric corneas. Furthermore, the peripheral cornea and limbus should be thoroughly assessed for abnormalities (pterygium, pannus, prominent Schwalbes line) that may affect the peripheral corneal and paralimbal shape. In these cases, the lens will need to be smaller than 93 to 97% of the HVID as abnormalities are typically raised, or significant flatter than the adjacent cornea.

EyeSpace Screen

Tear layer cross-section of the flat horizontal meridian which is designed to create 1.00D of steepening. Tear layer cross-section profile display from the centre to the edge: central steep zone, paracentral flatter curve, reverse curve, alignment curve and edge lift.

Tear layer cross-section of the steep vertical meridian which is designed to create 2.50D of flattening. Tear layer profile displays from the centre to the edge central flat zone, steeper reverse curve, alignment curve and edge lift.

Optical Analysis

A graph displaying the Tear Layer Power, Ocular refraction (OR), and Ideal BVP (Jessen Factor) of the lens.

Lens Delivery - Lens 1

One drop of 0.4% oxybuprocaine was inserted into both eyes prior to insertion of Forge Ortho-K lenses for the first time. Prior to insertion, the lenses were rinsed with saline to wash off any wetting solution the lens is stored in. This enables the lens to be better assessed with NaFl, blue light, and a Wratten yellow filter. A drop of saline was put in the back of the contact lens, and a NaFl strip dipped in the back of the lens creating a beautiful looking fluorescent green cocktail. The lens was then inserted with the patient’s eye in a face-down position while looking towards the ground.

NaFl assessment with Lens 1 on the eye

  • 1.00 mm of vertical movement on eye blink.
  • Good centration.
  • Correct lens size - slightly smaller than the corneal diameter.
  • Lens locating and stable as simulated.
  • Fitting exactly as the lens was designed to fit.
  • Vision with the lens on eye 6/5.
  • Refraction over the lens plano.

Orthokeratology Lens Accessories

  • Daily Cleaning Solution: Hydrogen Peroxide Solution - AOSept Plus with Hydraglyde
  • Insertion Solution: Non preserved lubricant with sodium hyaluronate - Hylo Forte
  • Rinsing Solution: Saline - Lens Plus
  • Monthly Intensive Cleaning: Menicare Progent
  • Removal Tool: DMV Ultra

Communication with the Patient

Lenses should be inserted 5 to 10 minutes before going to bed to allow time for the lens to settle. Though it is common to feel uncomfortable with your eyes open at first, this will improve with time and you should not notice any discomfort sleeping.

Following the first night of wear, the vision will be clearer although not perfect; about 50% of the total refractive change occurs after just one night. Your eyes may be sensitive and have some ‘sleep’ in them when you wake up. Take the lenses out immediately and this should improve. You may still need to use your glasses to drive to your appointment (this may be slightly blurry) or have someone take you.

First Morning Aftercare - Lens 1

The patient presented the next morning reporting no discomfort, irritation or disruption to sleep, was able to easily insert and remove the lens, and noted the vision is much improved following removal of the lens.

Corneal Topography Analysis

Axial Power difference map

Tangential Power difference map

Concerns

  • The technician who took topography did not centre the placido rings correctly.

Assessment

  • Great visual result for first night
  • Good centration
  • No corneal staining or infiltrate

Plan

  • Review in one week.
  • Patient education.
  • Use +1.00D readers if necessary.

One-month Aftercare - Lens 1

The patient failed to attend the practice at one week, rather only returned after a month. Patient reported vision was very good for the first 2 weeks and then has slowly worsened.

Corneal Topography Analysis

Axial Power difference map

Axial power difference map displays +1.00D in the horizontal meridian and -2.50 in the vertical.

Tangential Power difference map

Tangential power displaying a well-centred treatment zone.

Concerns

  • Overcorrection of the spectacle cylinder.

Assessment

  • Great centration
  • Corneal steepening in the horizontal meridian could be wider to create better optics

Plan

  • New lens with wider BOZD in the horizontal meridian and less cylinder correction.

Patient education

  • Continue wearing the lens 2 nights on, then one night off until the new lens arrives.

Lens 2

Design parameters

How was the design changed?

  • Flattened the horizontal and steepened the vertical BOZR to reduce the cyl correction
  • Widened the BOZD in the horizontal meridian.

EyeSpace Screen

Tear layer cross-section of the flat horizontal meridian.

Tear layer cross-section of the steep vertical meridian.

Optical Analysis

Delivery Lens 2

NaFl assessment with the lens on the eye

No picture was taken. Good centration, 1.00-2.00 mm of lens movement on blink. NaFl pattern as simulated.

Over Refraction

Plano VA: 6/5

Advice and management

Review in one week.

Aftercare following one week after wearing lens 2

Very happy with distance vision, however, needs to wear +1.50 for reading.

Corneal Topography

Axial Power difference map

Axial power difference map displays +1.00D in the horizontal meridian and -1.75D in the vertical.

Tangential Power difference map

Tangential power displaying a well-centred treatment zone.

Concerns

  • Need for better near vision.

Assessment

  • Great centration.
  • Great correction of distance vision.

Plan

  • Review in one month.

Aftercare following six weeks of wearing lens 2

Patient reports great distance vision, however, requires +1.00 magnifiers for reading and computer work.

Corneal Topography

Axial Power difference map

Axial power difference map displays +0.75D in the horizontal meridian and -1.75D in the vertical.

Tangential Power difference map

Tangential power displaying a well-centered zone.

Concerns

  • Needs better near vision

Assessment

  • Extra +1.00 gives N4 near vision

Plan

  • A new lens designed with extra plus correction and wider BOZD.

Patient Education

  • Continue wearing the current lens.

Lens 3

Design Parameters

How was the design changed?

  • Steepened BOZR in both meridians
  • Widened the BOZD in the horizontal meridian.

EyeSpace Screen

Tear layer cross-section of the flat horizontal meridian.

Tear layer cross-section of the steep vertical meridian.

Optical Analysis

Lens Delivery (Lens 3)

Patient picked up lens without lens assessment.

Aftercare following three weeks of wearing lens 3

Notes the near vision is better, although variable. Distance vision still very good.

Corneal Topography

Axial Power difference map

Axial power difference map displays +1.50D in the horizontal meridian and -1.50D in the vertical.

Tangential Power difference map

Tangential power displaying a well-centred zone.

Concerns

  • Still needs better near vision.

Assessment

  • The new lens is giving more plus correction.
  • Overcorrection of the astigmatism.
  • The optic zone has widened from the previous design.

Plan

  • A new lens designed with extra plus correction.

Patient Education

  • Continue wearing the new lens.

Lens 4

Design Parameters

How was the design changed?

  • Steepened BOZR in both meridians 7.40/7.80
  • Widened the BOZD in the horizontal meridian.
  • Decreased the diameter to 11.00 mm and narrowed the edge width to 0.60 mm

EyeSpace Screen

Tear layer cross-section of the flat horizontal meridian.

Tear layer cross-section of the steep vertical meridian.

Optical Analysis

Aftercare following three months of wearing lens 4

The patient left for a missionary posting in the South Pacific and returned 3 months after starting to wear lens 4. He reported his near vision was much improved and was able to read his computer, smartphone, without the need for spectacles. He had no complaints about his distance vision and noted he was only having to wear +1.00 specs when looking at very small detail.

Corneal Topography

Axial Power difference map

Axial power difference map displaying +2.00D of change in the horizontal meridian and -1.50D in the vertical meridian.

Tangential Power difference map

Concerns

  • None

Assessment

  • Very good balance of both distance and near vision without aids during the day

Plan

  • Review in 6 months

Patient Education

  • Continue wearing the lens every night.
  • Clean with Progent once a month
  • Must return for review in 6 months

Conclusion

Fitting mixed astigmatism certainly poses significant challenges, and in this case, four lenses were required to achieve a successful result. However, this case demonstrates it is possible with orthokeratology to steepen the cornea in the horizontal meridian and flatten the vertical meridian in order to correct WTR mixed astigmatism.

In time lens designs will continue to improve and the science and understanding of what is possible for orthokeratology vision correction will continue to improve. Cases like this would be impossible to fit without computer-aided contact lens simulation software such as EyeSpace. This case demonstrates that orthokeratology is not simply for patients with low myopia, and for myopia control, it is a fantastic correction option for presbyopes.