- Email: [email protected]
Clinical experience with CAB lenses
Clinical Experience with CAB Lenses Franz D. Arens
A graduate of Cologne High School of Optometry, Dr. Arens has own contact lens practice and acts as research and development consultant to Titmus Eurocon.
During the last 25 months gas permeable hard contact lenses have been fitted more frequently for various reasons, either as initial fitting or in the case of incompatibility with other contact lenses. Methods to define these diverse new materials have become more and more differential. Due to the lack of technical possibilities the practitioner can hardly record these subtle, physical-chemical differences any more. Therefore, our results will only be based on practical, empirical values.
of first study. A complete evaluation of the clinical results will only be possible at a later time. We would like to point out that our study is limited to the 260 lenses which had been fitted to "normal eyes", keratoconus and aphakia, being special subjects, have been excluded. Patients of the age of nine to 47 years were fitted. O n principle these patients were from two groups, one group had already worn lenses before, and another group were being fitted for the first time. While CAB lenses had been used right from the beginning for 196 eyes, 64 eyes already wearing lenses were re-fitted with CAB lenses. Out of these 64 lenses 46 soft and 18 hard lenses were changed. Reasons for changing are shown in Table II.
Materials and Methods The chemical - - physical properties of the used Persecon lenses were indicated by TITMUS E U R O C O N as shown in Table I. The clinical trials for this material were carried out by the University hospital eye departments at Ulm and Mainz. They gave their clearance certificates, toxicological - - and microbiological - - wise. So the material got the approval of the German Ministry of Health. Altogether 351 eyes, 52 of those with keratoconus and 39 with aphakia, have been provided with lenses and systematically controlled since mid-January 1977. Comparative fittings R / L were also made in some cases. However, not all long wearing tests lasting 20 months have already been terminated or evaluated, so that the results obtained can be regarded as a kind
"Speetack Blur" R ~ for ~ ¢~fort (general)
PMMA
16.8
water content %
refractive index
7.6 --+13
1.2--1.3
app. 0.4
t .49
0.01
app. 2
1.47
O.30
linear t h e ~ a [ expansion mm/
1.18---1.21
O, pe~eability 10-' cm ~. ~ c
m e a n molecular weight
fusing temp. °C
contact angle °
cond. of warmth W mk
PMMA
150.00(I
293
74
d,[9
70.10 -~
CAB
120.~1
140
63
o.~
104.10-'
overwearing
14
6
edema
spectacle blur
' bulb ~ n j injection
syndrom
2
6 4
12 4
follicular Iotal hyper eyes trophy 6 46 HEMA 18 PMMA
Eyes, with corneal damage, were not fitted until the physiological normal state had been regained. The range of powers of ametropia covered by these 260 eyes is shown in Table VII. The spectacle cylinder correction found ranged from p i a n o t o - - 6.50 dpts. Before fitting a full eye examination was performed from a standardized, diagnostic list. The state of the fitted eyes and parameters of the used lenses were systematically checked. Follow-up visits were generally performed after at least four hours of wear. As a rule, the intervals between the visits were six days, two weeks, six weeks, three months and six months after dispensing the lenses. Further visits in shorter intervals were arranged if necessary. The fitting was made on a mere selective basis with lenses of PMMA - - except in the case of aphakia and
+2 CAB
limited wearing time 4
2
CAB - - PMMA density
limited visual acuity
Table II
Chmtod-~raad Pre~e~ hardness kp/mm a
to CAB k'm~
Table I
30
h a d to b e c o m p e n s a t e d with the f r o n t toric surface. Prismatic f r o n t - t o r i c lenses were fitted like n o r m a l spherical lenses of the same d i a m e t e r with a prism ballast as low as possible a n d a t e n d e n c y for a " s t e e p " fit so as to avoid t h e sliding d o w n especially in weak m i n u s a n d plus powers.
Comparison of Corrected Deficiencies of Vision without Keratoconus and Aphakia
upto+ 7.5 + 5.0 + 2.5 piano - 2.5 - 5.0 - 7.5 - 10.0 - 15.0
- 20.0 over - 20.0
eyes 2 7 19
% 0.75 2.80 7.30
83 67 41 23 9 4 5
31.95 25.75 15.76 8.85 3.45 1.50 1.90
Results
T a b l e III shows t h e f r e q u e n c y of types of lenses used with t h e s e 260 fittings. T h e f r e q u e n c y o f d i a m e t e r s used a n d their relation to the h o r i z o n t a l visible iris d i a m e t e r is evaluated in T a b l e s V a n d VI. O f course, this s t a t e m e n t is only a p p l i c a b l e with r e g a r d to the horizontal corneal d i a m e t e r . T h e factors, lid a p e r t u r e a n d position as well as lid tension are n o t t a k e n into consideration.
Table VII Compm-~m of "Pypes of Lens~ Used
1 sph. BCOR II sph. BCOR
with ~ph. periph, flattening with toric periph, flat tening and sph. front OZ with toric periph, flat tening and sph. front OZ with toric periph, flattening and tori¢ front OZ wit h asph. pelfph, flattening and tori¢ front OZ incl. pl%m ballast without truncation
I11 toric BCOR IV ~oric BCOR V sph. BCOR
total
P~ 3l
76[~5 11.95
15
5.75
9
3.45
6
2.30
260
100.00
Comparison of Diameters Used
OD OD OD OD OD OD OD
k e r a t o c o n u s - - h a v i n g a g e o m e t r y identical to that of C A B lenses. T h e guide lines o n which these fittings w e r e b a s e d are i n d i c a t e d in T a b l e I V a n d aimed at a c o n c e n t r i c to a possibly m o d e s t steep fit. A s it b e c a m e e v i d e n t , it s e e m s easier to fit lenses of C A B material s o m e w h a t s t e e p e r t h a n identical o n e s o u t of P M M A , w i t h o u t a n y s y m p t o m s of m e t a b o l i c disturbances resulting. P e r i p h e r a l toric lenses were fitted approx. 0. l m m s t e e p e r t h a n lenses with n o r m a l spheric peripheral f l a t t e n i n g o f the s a m e diameter.
total
pces 4 26 102 95 22 9 2
% 1.50 10.00 39.25 36.55 8.50 3.45 0.75
260
100.00
Table V Diameters Used in Relation to the Horizontal Corneal Diameter 260Pc~
(30 8.0,,,, [] 00 8.5ram [ ] OD 90 m,. [ ]
GO 9.5.,,, [] 00100,,,, [] OD 105,~n [] OD 11.0ram []
ISZ
Fitting Guidelines
156
diameter
base curve
as small as possible, as large as necessary
with medium corneal ~) and medium lens and medium corneal radii rl
8.0 mm 8.5 mm 9.0mm 9.5 mm 10.0 mm 10.5 mm 11.0 mm
+ 2
:tl .o0m 26
r2+ 0.1
ml,..
2 .4 6 Blto .2 4 .6 .812o.2 / . . 6
_
.8
Table VI Table IV
T a b l e V I I I shows the lenses fitted in relation to the eyes p r o v i d e d . T h e m e a n value of lenses fitted per eye was d e t e r m i n e d . T h e fact that a change from H E M A to C A B lenses r e q u i r e s m u c h m o r e effort t h a n initial fitting o n p a t i e n t s s e e m e d very interesting to us. W e t h i n k t h a t this is d u e to the fact that soft lens wearers h a d to b e fitted with C A B lenses without the absolute,, initial c o r n e a l radii b e i n g known. A n o t h e r r e a s o n was d i s t o r t e d k e r a t o m e t e r mires due to
W h e n possible, back-toric lenses were fitted with a small cylinder t h a t is to say parallel to the flatter c o r n e a l m e r i d i a n a n d flat to the steeper corneal m e r i d i a n . A s a rule, the toric difference of the cylinder c o r r e s p o n d e d to 2 / 3 of the corneal astigmatism. In some cases lenses were fitted in b o t h m e r i d i a n s 0.05 to 0 . 1 m m s t e e p e r than the corneal radii. In these cases, s t r o n g e r induced astigmatism
32
Lid tension strong strong T h e following h a r d P M M A lenses were fitted: 7.9 / - 4.0 / 9.5 7.85 / - 3.5 / 9.5 VA 1.2 + 1.5 + T h e s e lenses, giving optimal visual acuity, were worn w i t h o u t any p r o b l e m s . T h e a d a p t a t i o n p e r i o d of four w e e k s was r a t h e r long. Miss H. is working as a s t e w a r d e s s a n d w a n t e d to take o u t t h e lenses from time to time o n long trips. T h e r e f o r e , spectacles, w h i c h s h e could w e a r alternately with her lenses, b e c a m e necessary. Several times we tried to get an acceptable visual acuity with spectacle Rx, however, w i t h o u t any success. A f t e r s e v e n m o n t h s of wearing hard lenses t h e following c o r n e a l radii were m e a s u r e d :
Lenses Fitted a n d Changed During the First 3 Months
eyes
CL fitted
mean value
first equipment
196
287
1.46
changed from HEMA to CAB
46
137
2.97
changed from PMMA to CAB
18
43
2.38
Table VIII Indications
when conventional hard lenses are not tolerated - - considerable metabolic disturbance - - short weaiing time with PMMA lenses - - constant insufficient O2-environmentcondition - - in case of allergies against PMMA or HEMA lenses and/or their solutions - - aphakia - - keratoconus - necessary steep fitting of hard lens - - necessary large overall diameter of hard lens - - as alternative to complicated soft toric lenses --
R
8.00 vert. 8.15 hori.
in case of high sensibility lack of good handling and maintenance (scratching) sport, under some circumstances limited suitability
Table IX P M M A lenses so t h a t the C A B lenses had to b e r e - a d a p t e d gradually to the new conditions. H e r e b y we h a v e to take into consideration t h a t with increasing e x p e r i e n c e in c o m p a r i n g the diverse m a t e r i a l s , differences s h o w n should n o w s o m e w h a t level out. Case
Report
(This lady was fitted with haptics from a good impression.) In t h e following we would like to d e m o n s t r a t e two cases o f interest to us: 1) Miss F.H. 23 years, was successfully wearing h y d r o p h i l i c lenses not totally correcting her astigm a t i s m , for o v e r two years; w h e n , due to new p r o f e s s i o n a l activities, an o p t i m a l visual acuity bec a m e necessary for her, the correction of the astigm a t i s m neglected so far was n e e d e d . In o r d e r to get best c o n d i t i o n s for a new fitting of h a r d lenses, she s t o p p e d w e a r i n g h e r soft ones for two weeks. T h e n the following data was collected: Refr. VA K'read. Cornea Lid ap.
R
L
- 3 . 0 / 0.75 x 180 ° 1.2 (-4) 8.0 7.73 11.0 4.5
- 2 . 2 5 / - 0 . 7 5 × 5° 1.2 (-1) 7.95 7.60 11.0 4.5
1 h after lens removal
7.88 vert. 7.75 vert. ( 34 h after removal of 8.10 hori. 8.08 hori. J h a r d lenses T h e m i r e s were always distorted, visual acuity R / L a c h i e v e d was 0 . 7 . A s a test, P M M A lenses were c h a n g e d for C A B lenses h a v i n g identical p a r a m e t e r s . W i t h a constant g o o d visual acuity a n d best tolerance the following radii w e r e m e a s u r e d after a wearing time of t h r e e months: 7.76 vert. 7.65 vert. 8.05 hori. 8.05 hori. T h e n Miss H. got spectacles with the following prescription: - 3.50 / - 0.75 - 2.75 / - 0.75 x 180 ° x 5° T h e s e spectacles are now worn alternately with c o n t a c t lenses, with great success, the occurrence of spectacle blur is only very rare a n d m u c h m o r e r e d u c e d . Miss H. considers the visual acuity achieved with spectacles, e v e n shortly after the change from c o n t a c t lenses, as very good. 2) Mr. A . N . , 36 years, h a d not worn any lenses at all, h o w e v e r , h e w a n t e d to d o so because of his professional activities a n d for reasons of sport. T h e following interesting data was m e a s u r e d at the first fitting session:
Contraindications ----
L
7.80 vert. 8.20 hori. J
R
L
Refr. -1.5/-1.5x 15 ° - 2 . 2 5 / - 1 . 0 x 170° VA 1.0 ( - 6 ) 1.2 ( + 4 ) K'read. 8.12 7.80 8.10 7.90 Cornea 11.5 11.5 Lid ap. 5.5 5.5 Lid tension strong strong Dilatation light 3.0 3.0 dark 6.0 6.0 T h e fitting of soft toric lenses failed mostly because an exact stabilization of the lenses could not be achieved. Mr. N ' s first P M M A lenses h a d the
33
following parameters: 8.05 / -2.25 / 9.50 8.10 / -2.50 / 9.00 With these lenses the visual acuity was not stable and the foreign body sensation very strong. Above all light reflections at night were considered as very disturbing. Then lenses having a diameter of 10.00mm and an O Z of 8.0 were fitted. With these the light reflections seemed somewhat reduced. Then we tried even larger lenses until following data were achieved and considered as optimal: 8.20 / - 1.75 / 11.00 8.25 / - 2 . 0 0 / 11.00 VA 1.3 1.5 These lenses showed a normal "soft" sliding after blinking and the centering was optimal. The discomfort and symptoms mentioned above were eradicated. The larger diameter, however, allowed a maximum wearing time of 8 hours only. Because of this we changed to identical lenses out of CAB material which can now be worn up to 14 hours daily. The patient considers the general comfort and tolerance as optimal.
PMMA trial lenses, due to the different water content. Differences in fit and power can become evident and require subsequent additional refractions. Therefore it seemed advisable to us, to use high powered CAB trial lenses and thereby get a more exact over-refraction. Above all, with aphakia and keratoconus CAB trial lenses have proved t o be optimal. Of 64 eyes refitted with CAB lenses only eight were not successful; in the two cases of bulbar conjunctivital injection no improvement was achieved; the two eyes showing overwear syndrome would not tolerate the new lenses, and the four cases of limited visual acuity with HEMA lenses were discontinued due to general discomfort. The 196 eyes fitted with CAB lenses initially showed after 12 months, 10 failures; four patients could not adapt to the sensation of foreign body and were never really satisfied, one other patient did not have the necessary smooth touch to handle these lenses, scratching them beyond use within a few weeks. We tested different care solutions and methods. We wanted to possibly simplify the care system for the wearer without making any concessions with regard to cleaning and disinfecting of the lenses. A simple and efficient solution seems to be AUtotal, if necessary with LC 65 or Titan. Since TITMUS E U R O C O N is re-smoothing the surface of CAB lenses in a new physical-chemical way, a sporadic, inadequate wetting of the lens surface has become rare. To patients with rough hands who scratched the lens surfaces during cleaning within a short time, the Hydramat was given. At present no prediction can be made with regard to mean durability of CAB lenses. Certainly it is above that of soft lenses and, if correctly cared for, nearly the same as PMMA lenses.
Discussion In general it seems that, compared with PMMA lenses, CAB lenses may be fitted steeper without any occurrence of symptomatic metabolic disturbances. No significant staining was seen and only 5 eyes had a tendency for oedema. While PMMA lenses were fitted rather concentrically, a slightly steeper fit was desired for CAB lenses. Thereby, centering of the lenses was better and there were less foreign body sensations than with lenses fitted in a concentric way. The choice of diameter with CAB lenses seems easier since the limit upwards and consequently the larger covering of the corneal surface is not as restricted as with PMMA lenses. Above all with high lid tension or wide lid apertures better results could be obtained with larger diameters. In some cases of corneas with differences in radii between 0.4 to 0.7mm a normal spherical lens with a larger diameter, instead of an equivalent peripheral-toric lens, was successfully fitted. With toric corneas a large diameter CAB lens seems to be indicated since it is possible to achieve good vision and excellent tolerance with spherical or peripheral-toric lenses rather than using a toric or bitoric lens. Unless the lenses are kept fully hydrated alteration in fit and power can occur, due to an increased wet/ dry cycle. This applies especially to high minus lenses, as alterations in fit and power can occur when they are not constantly kept wet. Our studies have shown that a systematic recorrecting of the power is not necessary. If, however, highei" plus or minus CAB lenses are fitted, special care should be taken to the wet-dry-cycle of the used
Conclusion CAB lenses are certainly an essential new part of the lens palette which is at the practitioner's disposal. Patients do adapt quicker and easier to CAB lenses. The wearing schedule given to patients was four hours on the first day with a two hours break after two hours, increasing the wearing time half an hour per day alternating morning and afternoon. It is evident that CAB lenses also have negative aspects and show contra indications. In Table IX we have tried to list indications and contra-indications found. Certainly, the possibilities offered by the CAB lenses either with regard to variations or wider optimal choice of diameter and base curve render this lens a good alternative to conventional PMMA lenses.
34
A graduate of Cologne High School of Optometry, Dr. Arens has own contact lens practice and acts as research and development consultant to Titmus Eurocon.
During the last 25 months gas permeable hard contact lenses have been fitted more frequently for various reasons, either as initial fitting or in the case of incompatibility with other contact lenses. Methods to define these diverse new materials have become more and more differential. Due to the lack of technical possibilities the practitioner can hardly record these subtle, physical-chemical differences any more. Therefore, our results will only be based on practical, empirical values.
of first study. A complete evaluation of the clinical results will only be possible at a later time. We would like to point out that our study is limited to the 260 lenses which had been fitted to "normal eyes", keratoconus and aphakia, being special subjects, have been excluded. Patients of the age of nine to 47 years were fitted. O n principle these patients were from two groups, one group had already worn lenses before, and another group were being fitted for the first time. While CAB lenses had been used right from the beginning for 196 eyes, 64 eyes already wearing lenses were re-fitted with CAB lenses. Out of these 64 lenses 46 soft and 18 hard lenses were changed. Reasons for changing are shown in Table II.
Materials and Methods The chemical - - physical properties of the used Persecon lenses were indicated by TITMUS E U R O C O N as shown in Table I. The clinical trials for this material were carried out by the University hospital eye departments at Ulm and Mainz. They gave their clearance certificates, toxicological - - and microbiological - - wise. So the material got the approval of the German Ministry of Health. Altogether 351 eyes, 52 of those with keratoconus and 39 with aphakia, have been provided with lenses and systematically controlled since mid-January 1977. Comparative fittings R / L were also made in some cases. However, not all long wearing tests lasting 20 months have already been terminated or evaluated, so that the results obtained can be regarded as a kind
"Speetack Blur" R ~ for ~ ¢~fort (general)
PMMA
16.8
water content %
refractive index
7.6 --+13
1.2--1.3
app. 0.4
t .49
0.01
app. 2
1.47
O.30
linear t h e ~ a [ expansion mm/
1.18---1.21
O, pe~eability 10-' cm ~. ~ c
m e a n molecular weight
fusing temp. °C
contact angle °
cond. of warmth W mk
PMMA
150.00(I
293
74
d,[9
70.10 -~
CAB
120.~1
140
63
o.~
104.10-'
overwearing
14
6
edema
spectacle blur
' bulb ~ n j injection
syndrom
2
6 4
12 4
follicular Iotal hyper eyes trophy 6 46 HEMA 18 PMMA
Eyes, with corneal damage, were not fitted until the physiological normal state had been regained. The range of powers of ametropia covered by these 260 eyes is shown in Table VII. The spectacle cylinder correction found ranged from p i a n o t o - - 6.50 dpts. Before fitting a full eye examination was performed from a standardized, diagnostic list. The state of the fitted eyes and parameters of the used lenses were systematically checked. Follow-up visits were generally performed after at least four hours of wear. As a rule, the intervals between the visits were six days, two weeks, six weeks, three months and six months after dispensing the lenses. Further visits in shorter intervals were arranged if necessary. The fitting was made on a mere selective basis with lenses of PMMA - - except in the case of aphakia and
+2 CAB
limited wearing time 4
2
CAB - - PMMA density
limited visual acuity
Table II
Chmtod-~raad Pre~e~ hardness kp/mm a
to CAB k'm~
Table I
30
h a d to b e c o m p e n s a t e d with the f r o n t toric surface. Prismatic f r o n t - t o r i c lenses were fitted like n o r m a l spherical lenses of the same d i a m e t e r with a prism ballast as low as possible a n d a t e n d e n c y for a " s t e e p " fit so as to avoid t h e sliding d o w n especially in weak m i n u s a n d plus powers.
Comparison of Corrected Deficiencies of Vision without Keratoconus and Aphakia
upto+ 7.5 + 5.0 + 2.5 piano - 2.5 - 5.0 - 7.5 - 10.0 - 15.0
- 20.0 over - 20.0
eyes 2 7 19
% 0.75 2.80 7.30
83 67 41 23 9 4 5
31.95 25.75 15.76 8.85 3.45 1.50 1.90
Results
T a b l e III shows t h e f r e q u e n c y of types of lenses used with t h e s e 260 fittings. T h e f r e q u e n c y o f d i a m e t e r s used a n d their relation to the h o r i z o n t a l visible iris d i a m e t e r is evaluated in T a b l e s V a n d VI. O f course, this s t a t e m e n t is only a p p l i c a b l e with r e g a r d to the horizontal corneal d i a m e t e r . T h e factors, lid a p e r t u r e a n d position as well as lid tension are n o t t a k e n into consideration.
Table VII Compm-~m of "Pypes of Lens~ Used
1 sph. BCOR II sph. BCOR
with ~ph. periph, flattening with toric periph, flat tening and sph. front OZ with toric periph, flat tening and sph. front OZ with toric periph, flattening and tori¢ front OZ wit h asph. pelfph, flattening and tori¢ front OZ incl. pl%m ballast without truncation
I11 toric BCOR IV ~oric BCOR V sph. BCOR
total
P~ 3l
76[~5 11.95
15
5.75
9
3.45
6
2.30
260
100.00
Comparison of Diameters Used
OD OD OD OD OD OD OD
k e r a t o c o n u s - - h a v i n g a g e o m e t r y identical to that of C A B lenses. T h e guide lines o n which these fittings w e r e b a s e d are i n d i c a t e d in T a b l e I V a n d aimed at a c o n c e n t r i c to a possibly m o d e s t steep fit. A s it b e c a m e e v i d e n t , it s e e m s easier to fit lenses of C A B material s o m e w h a t s t e e p e r t h a n identical o n e s o u t of P M M A , w i t h o u t a n y s y m p t o m s of m e t a b o l i c disturbances resulting. P e r i p h e r a l toric lenses were fitted approx. 0. l m m s t e e p e r t h a n lenses with n o r m a l spheric peripheral f l a t t e n i n g o f the s a m e diameter.
total
pces 4 26 102 95 22 9 2
% 1.50 10.00 39.25 36.55 8.50 3.45 0.75
260
100.00
Table V Diameters Used in Relation to the Horizontal Corneal Diameter 260Pc~
(30 8.0,,,, [] 00 8.5ram [ ] OD 90 m,. [ ]
GO 9.5.,,, [] 00100,,,, [] OD 105,~n [] OD 11.0ram []
ISZ
Fitting Guidelines
156
diameter
base curve
as small as possible, as large as necessary
with medium corneal ~) and medium lens and medium corneal radii rl
8.0 mm 8.5 mm 9.0mm 9.5 mm 10.0 mm 10.5 mm 11.0 mm
+ 2
:tl .o0m 26
r2+ 0.1
ml,..
2 .4 6 Blto .2 4 .6 .812o.2 / . . 6
_
.8
Table VI Table IV
T a b l e V I I I shows the lenses fitted in relation to the eyes p r o v i d e d . T h e m e a n value of lenses fitted per eye was d e t e r m i n e d . T h e fact that a change from H E M A to C A B lenses r e q u i r e s m u c h m o r e effort t h a n initial fitting o n p a t i e n t s s e e m e d very interesting to us. W e t h i n k t h a t this is d u e to the fact that soft lens wearers h a d to b e fitted with C A B lenses without the absolute,, initial c o r n e a l radii b e i n g known. A n o t h e r r e a s o n was d i s t o r t e d k e r a t o m e t e r mires due to
W h e n possible, back-toric lenses were fitted with a small cylinder t h a t is to say parallel to the flatter c o r n e a l m e r i d i a n a n d flat to the steeper corneal m e r i d i a n . A s a rule, the toric difference of the cylinder c o r r e s p o n d e d to 2 / 3 of the corneal astigmatism. In some cases lenses were fitted in b o t h m e r i d i a n s 0.05 to 0 . 1 m m s t e e p e r than the corneal radii. In these cases, s t r o n g e r induced astigmatism
32
Lid tension strong strong T h e following h a r d P M M A lenses were fitted: 7.9 / - 4.0 / 9.5 7.85 / - 3.5 / 9.5 VA 1.2 + 1.5 + T h e s e lenses, giving optimal visual acuity, were worn w i t h o u t any p r o b l e m s . T h e a d a p t a t i o n p e r i o d of four w e e k s was r a t h e r long. Miss H. is working as a s t e w a r d e s s a n d w a n t e d to take o u t t h e lenses from time to time o n long trips. T h e r e f o r e , spectacles, w h i c h s h e could w e a r alternately with her lenses, b e c a m e necessary. Several times we tried to get an acceptable visual acuity with spectacle Rx, however, w i t h o u t any success. A f t e r s e v e n m o n t h s of wearing hard lenses t h e following c o r n e a l radii were m e a s u r e d :
Lenses Fitted a n d Changed During the First 3 Months
eyes
CL fitted
mean value
first equipment
196
287
1.46
changed from HEMA to CAB
46
137
2.97
changed from PMMA to CAB
18
43
2.38
Table VIII Indications
when conventional hard lenses are not tolerated - - considerable metabolic disturbance - - short weaiing time with PMMA lenses - - constant insufficient O2-environmentcondition - - in case of allergies against PMMA or HEMA lenses and/or their solutions - - aphakia - - keratoconus - necessary steep fitting of hard lens - - necessary large overall diameter of hard lens - - as alternative to complicated soft toric lenses --
R
8.00 vert. 8.15 hori.
in case of high sensibility lack of good handling and maintenance (scratching) sport, under some circumstances limited suitability
Table IX P M M A lenses so t h a t the C A B lenses had to b e r e - a d a p t e d gradually to the new conditions. H e r e b y we h a v e to take into consideration t h a t with increasing e x p e r i e n c e in c o m p a r i n g the diverse m a t e r i a l s , differences s h o w n should n o w s o m e w h a t level out. Case
Report
(This lady was fitted with haptics from a good impression.) In t h e following we would like to d e m o n s t r a t e two cases o f interest to us: 1) Miss F.H. 23 years, was successfully wearing h y d r o p h i l i c lenses not totally correcting her astigm a t i s m , for o v e r two years; w h e n , due to new p r o f e s s i o n a l activities, an o p t i m a l visual acuity bec a m e necessary for her, the correction of the astigm a t i s m neglected so far was n e e d e d . In o r d e r to get best c o n d i t i o n s for a new fitting of h a r d lenses, she s t o p p e d w e a r i n g h e r soft ones for two weeks. T h e n the following data was collected: Refr. VA K'read. Cornea Lid ap.
R
L
- 3 . 0 / 0.75 x 180 ° 1.2 (-4) 8.0 7.73 11.0 4.5
- 2 . 2 5 / - 0 . 7 5 × 5° 1.2 (-1) 7.95 7.60 11.0 4.5
1 h after lens removal
7.88 vert. 7.75 vert. ( 34 h after removal of 8.10 hori. 8.08 hori. J h a r d lenses T h e m i r e s were always distorted, visual acuity R / L a c h i e v e d was 0 . 7 . A s a test, P M M A lenses were c h a n g e d for C A B lenses h a v i n g identical p a r a m e t e r s . W i t h a constant g o o d visual acuity a n d best tolerance the following radii w e r e m e a s u r e d after a wearing time of t h r e e months: 7.76 vert. 7.65 vert. 8.05 hori. 8.05 hori. T h e n Miss H. got spectacles with the following prescription: - 3.50 / - 0.75 - 2.75 / - 0.75 x 180 ° x 5° T h e s e spectacles are now worn alternately with c o n t a c t lenses, with great success, the occurrence of spectacle blur is only very rare a n d m u c h m o r e r e d u c e d . Miss H. considers the visual acuity achieved with spectacles, e v e n shortly after the change from c o n t a c t lenses, as very good. 2) Mr. A . N . , 36 years, h a d not worn any lenses at all, h o w e v e r , h e w a n t e d to d o so because of his professional activities a n d for reasons of sport. T h e following interesting data was m e a s u r e d at the first fitting session:
Contraindications ----
L
7.80 vert. 8.20 hori. J
R
L
Refr. -1.5/-1.5x 15 ° - 2 . 2 5 / - 1 . 0 x 170° VA 1.0 ( - 6 ) 1.2 ( + 4 ) K'read. 8.12 7.80 8.10 7.90 Cornea 11.5 11.5 Lid ap. 5.5 5.5 Lid tension strong strong Dilatation light 3.0 3.0 dark 6.0 6.0 T h e fitting of soft toric lenses failed mostly because an exact stabilization of the lenses could not be achieved. Mr. N ' s first P M M A lenses h a d the
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following parameters: 8.05 / -2.25 / 9.50 8.10 / -2.50 / 9.00 With these lenses the visual acuity was not stable and the foreign body sensation very strong. Above all light reflections at night were considered as very disturbing. Then lenses having a diameter of 10.00mm and an O Z of 8.0 were fitted. With these the light reflections seemed somewhat reduced. Then we tried even larger lenses until following data were achieved and considered as optimal: 8.20 / - 1.75 / 11.00 8.25 / - 2 . 0 0 / 11.00 VA 1.3 1.5 These lenses showed a normal "soft" sliding after blinking and the centering was optimal. The discomfort and symptoms mentioned above were eradicated. The larger diameter, however, allowed a maximum wearing time of 8 hours only. Because of this we changed to identical lenses out of CAB material which can now be worn up to 14 hours daily. The patient considers the general comfort and tolerance as optimal.
PMMA trial lenses, due to the different water content. Differences in fit and power can become evident and require subsequent additional refractions. Therefore it seemed advisable to us, to use high powered CAB trial lenses and thereby get a more exact over-refraction. Above all, with aphakia and keratoconus CAB trial lenses have proved t o be optimal. Of 64 eyes refitted with CAB lenses only eight were not successful; in the two cases of bulbar conjunctivital injection no improvement was achieved; the two eyes showing overwear syndrome would not tolerate the new lenses, and the four cases of limited visual acuity with HEMA lenses were discontinued due to general discomfort. The 196 eyes fitted with CAB lenses initially showed after 12 months, 10 failures; four patients could not adapt to the sensation of foreign body and were never really satisfied, one other patient did not have the necessary smooth touch to handle these lenses, scratching them beyond use within a few weeks. We tested different care solutions and methods. We wanted to possibly simplify the care system for the wearer without making any concessions with regard to cleaning and disinfecting of the lenses. A simple and efficient solution seems to be AUtotal, if necessary with LC 65 or Titan. Since TITMUS E U R O C O N is re-smoothing the surface of CAB lenses in a new physical-chemical way, a sporadic, inadequate wetting of the lens surface has become rare. To patients with rough hands who scratched the lens surfaces during cleaning within a short time, the Hydramat was given. At present no prediction can be made with regard to mean durability of CAB lenses. Certainly it is above that of soft lenses and, if correctly cared for, nearly the same as PMMA lenses.
Discussion In general it seems that, compared with PMMA lenses, CAB lenses may be fitted steeper without any occurrence of symptomatic metabolic disturbances. No significant staining was seen and only 5 eyes had a tendency for oedema. While PMMA lenses were fitted rather concentrically, a slightly steeper fit was desired for CAB lenses. Thereby, centering of the lenses was better and there were less foreign body sensations than with lenses fitted in a concentric way. The choice of diameter with CAB lenses seems easier since the limit upwards and consequently the larger covering of the corneal surface is not as restricted as with PMMA lenses. Above all with high lid tension or wide lid apertures better results could be obtained with larger diameters. In some cases of corneas with differences in radii between 0.4 to 0.7mm a normal spherical lens with a larger diameter, instead of an equivalent peripheral-toric lens, was successfully fitted. With toric corneas a large diameter CAB lens seems to be indicated since it is possible to achieve good vision and excellent tolerance with spherical or peripheral-toric lenses rather than using a toric or bitoric lens. Unless the lenses are kept fully hydrated alteration in fit and power can occur, due to an increased wet/ dry cycle. This applies especially to high minus lenses, as alterations in fit and power can occur when they are not constantly kept wet. Our studies have shown that a systematic recorrecting of the power is not necessary. If, however, highei" plus or minus CAB lenses are fitted, special care should be taken to the wet-dry-cycle of the used
Conclusion CAB lenses are certainly an essential new part of the lens palette which is at the practitioner's disposal. Patients do adapt quicker and easier to CAB lenses. The wearing schedule given to patients was four hours on the first day with a two hours break after two hours, increasing the wearing time half an hour per day alternating morning and afternoon. It is evident that CAB lenses also have negative aspects and show contra indications. In Table IX we have tried to list indications and contra-indications found. Certainly, the possibilities offered by the CAB lenses either with regard to variations or wider optimal choice of diameter and base curve render this lens a good alternative to conventional PMMA lenses.
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