By Dr. Bruce Anderson
Case 1: Radial Keratomy Failure
Patient: 66-year-old Female
This patient was seen on 10/22/04 for evaluation of irritation to her right eye when wearing her contact lenses. She had a history of 16 cut RK surgery to both eyes in 1986. She was unsure of her original glasses correction before surgery but believed it to be around -8.00 diopters. No records are available to confirm this. She had been wearing GP lenses for the past 8 years because of variable and unsatisfactory VA with glasses.
OD: 20/40 with current contact lens
+0.25 => 20/40
Slit Lamp Evaluation
Under the microscope, it was noted that the contact lens was slightly decentered superior/nasal and was adherent to the cornea. There was no movement upon forced blink. The cornea revealed 16 radial incisions leaving a 3.5 mm. clear zone centrally. There were iron pigment deposits centrally. 1+ superficial corneal staining was located central to superior nasal. There was no significant staining in the region of the incisions. The remainder of the slit lamp evaluation was normal except for a slight nuclear cataract.
The Patient was taken out of her contact lens and asked to return in one to two weeks for a refit of the lens in her right eye.
Diagnostic Data at Fitting Visit
OD: +3.50 -2.75 x 010 20/40-
OD: 36.75 / 38.00 @ 119
I proceeded with a lens refitting using a gas permeable plateau contact lens design.
OD: 39.00 / 10.0 / Plano / Reverse curve 42.00 (3D)
BC / Dia / Power
+3.00 => 20/40 acuity
The initial trial lens was chosen based on the topography measurements at the 5 mm. ring region (ranges from 37 D to 41 D). This trial lens decentered slightly high with a slight central fluorescein pooling.
Initial Lens Ordered
OD: 39.25 / +2.75 / 10.2 / 8.2 / .5/7.99 .3/8.99 .2/11.50
BC / Power / Dia / OZ / PC
The contact lens centered well with a slight superior position. There was 1+ central fluorescein pooling which correlated with the flattened central region noted in topography. There was good edge lift and movement of the contact lens.
This patient was fit into a large diameter reverse geometry gas permeable lens. This lens design was chosen due to the flat central cornea created by the RK surgery. This fit was determined through the use of trial lenses (Plateau) which has numerous reverse geometries and base curves. The base curve ordered (as mentioned earlier) was based on topography readings at the 5 mm. ring. This allowed a good starting point. The reverse geometry curve was based on the change in the topography at the 8 to 9 mm. zone. The topography revealed a steepening in this region of about 3 diopters. Most gas permeable lens designs are based on the central corneal curvatures; however, with the RK surgery, the central cornea has become excessively flat and the contact lens will vault over this area. So essentially, the central cornea is ignored when choosing a trial lens.
The large diameter was chosen to enhance the “holding” ability of the contact lens on the eye. The reverse geometry allows the lens to “grip” the steepened peripheral cornea and hold position better. The peripheral curves are designed to create a flat edge with slight lift to enhance good movement. The final acuity was reduced due to the optical distortion from the RK incisions encroaching into the pupil region and from a slight nuclear cataract.
Case 2: Penetrating Keratoplasty
Patient: 51-year-old Female
This patient presented for a contact lens fitting for her right eye on December 13, 2004. She had a corneal transplant in 1985 for keratoconus in this eye. She was currently wearing contact lenses in both eyes. She was having problems of chronic irritation only in the right eye. She had been wearing gas permeable lenses for the last 25 years.
OD 20/25- with current contact lens
Slit Lamp Evaluation
The right contact lens was decentering inferior temporal. The lens was moving excessively. The fluorescein pattern revealed heavy bearing at 7:30 and 11:00 over the graft region. There was 2+ punctate staining in the region of the contact lens bearing. The graft was well healed and clear centrally. There were no remaining sutures in place. The graft was proud (plateauing) at 5:00 to 8:00. The contact lens was lifting away from the peripheral cornea in the region of this plateauing.
Diagnostic Data at Fitting
OD: Plano -5.25 x 060 20/70+
I proceeded with the contact lens fitting using a plateau gas permeable contact lens (my own design).
OD: 47.50 / -3.00 / 9.8 / 7.6 / .7/6.75 .2/8.10 .2/11.00
BC / Power/ Dia / OZ / PC
Reverse Geometry / Aspheric BC
-4.75 => 20/25 Acuity
The initial lens was chosen based on topography and her previous contact lens (which was analyzed):
Old Contact Lens OD:
-7.50 / 47.50 / 9.6
Power / BC / Dia
The central topography showed a tremendous amount of toricity. The flatter meridian (69º) corresponded with the region of her previous contact lens bearing. The region of high toricity was centered around the graft and in the flat meridian created the proud (or plateau) effect of the graft inferior.
Contact Lens Ordered
OD: 47.50 / -7.00 / 10.8 / 8.4 / .7/6.85 .2/8.20 .3/11.60
BC / Power / Dia / OZ / PC
Boston XO / Lenticular
In designing the final contact lens, the base curve was unchanged from the diagnostic trial lenses. To allow for better centration, a larger diameter was used. The decrease the edge lift off, a reverse geometry design was used. A fairly large reverse curve width was incorporated to allow the lens to fit over the edge of the plateau.
Dispensing of the contact lens revealed a well-centered lens with approximately 1 to 1 ½ mm. of movement. The edge lift noted previously was elevated. The lens was bearing in the 5:00 to 7:00 region and the 12:00 to 2:00 region on the graft. There was fluorescein pooling in the opposite axis. The acuity was 20/25-. The over refraction was +0.25 sphere => 20/25-.
When fitting a contact lens on a post penetrating keratoplasty, eye topography is essential. The large amount of corneal toricity measured was determined to be central and primarily affected the graft region. The graft was very proud (or plateauing) inferior. This created a very unique situation that may allow desiccation of the inferior cornea when a contact lens is worn.
I fit this eye with a reverse geometry design to allow the gas permeable lens to “follow the slope” of the graft interface and obtain better centration. I did have concerns about the high toricity centrally; however, with the trial lens, there was no air entrapment in the steep region. If this had occurred, a bitoric base curve with the reverse geometry could have been used. The initial base curve may be estimated by evaluating the 5 mm ring on the topography. This ranged from the steepest at approx. 56D to flattest at 43D. For normal toric corneas my rule of thumb for an initial base curve is 1/3 of the delta K readings added to the flat K reading. [ 1/3(56 – 43) ] + 43 = Approx 47.50D. For this cornea with mainly central toricity, this worked well. The reverse geometry curve and peripheral curves were loosed slightly as determined from the evaluation of the trial lens on the eye. The diameter was increased to allow the lens to fit over the edges of the interface. This would also enhance centration and create a tighter fit.