Lachlan Hoy
July 01, 2019
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.
Mixed Astigmatism and adjustment for overcorrection of the WTR astigmatism with the initial lens.
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
Fitted slightly flatter than the cornea to increase the negative suction effect (Flat meridian only)
Commonly referred to as a reverse curve, controls the overall depth and the clearance of the edge of the back optic 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.
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.
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.
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.
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.
A graph displaying the Tear Layer Power, Ocular refraction (OR), and Ideal BVP (Jessen Factor) of the lens.
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.
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.
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.
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.
Axial power difference map displays +1.00D in the horizontal meridian and -2.50 in the vertical.
Tangential power displaying a well-centred treatment zone.
Tear layer cross-section of the flat horizontal meridian.
Tear layer cross-section of the steep vertical meridian.
No picture was taken. Good centration, 1.00-2.00 mm of lens movement on blink. NaFl pattern as simulated.
Plano VA: 6/5
Review in one week.
Very happy with distance vision, however, needs to wear +1.50 for reading.
Axial power difference map displays +1.00D in the horizontal meridian and -1.75D in the vertical.
Tangential power displaying a well-centred treatment zone.
Patient reports great distance vision, however, requires +1.00 magnifiers for reading and computer work.
Axial power difference map displays +0.75D in the horizontal meridian and -1.75D in the vertical.
Tangential power displaying a well-centered zone.
Tear layer cross-section of the flat horizontal meridian.
Tear layer cross-section of the steep vertical meridian.
Patient picked up lens without lens assessment.
Notes the near vision is better, although variable. Distance vision still very good.
Axial power difference map displays +1.50D in the horizontal meridian and -1.50D in the vertical.
Tangential power displaying a well-centred zone.
Tear layer cross-section of the flat horizontal meridian.
Tear layer cross-section of the steep vertical meridian.
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.
Axial power difference map displaying +2.00D of change in the horizontal meridian and -1.50D in the vertical meridian.
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.