|Year : 1992 | Volume
| Issue : 3 | Page : 74-78
Maximal mydriasis evaluation in cataract surgery
Tony Ho, Richard Fan, Wong Wing Hong, Khoo Boo Khian
Dept. of Ophthalmology, Tan lock Seng General Hospital, Singapore 1130
Bascom Palmer Eye Institute, P.O. Box 016880, Miami, FL 33101, USA
Source of Support: None, Conflict of Interest: None
We propose the Maximal Mydriasis Test (MMT) as a simple and safe means to provide the cataract surgeon with objective and dependable pre-operative information on the idiosyncratic mydriatic response of the pupil. The MMT results of a consecutive series of 165 eyes from 100 adults referred for cataract evaluation are presented to illustrate its practical applications and value. The results of the MMT allows the surgeon to anticipate problem eyes pre-operatively so that he can plan his surgical strategy more appropriately and effectively. Conversely, the surgeon can also appropriately and confidently plan surgical procedures where wide pupillary dilation is important. The MMT has also helped improve our cost-effectiveness by cutting down unnecessary delays in the operating room and enabling better utilisation of restricted costly resources.
Keywords: Maximal mydriasis test, cataract surgery, cost-effectiveness
|How to cite this article:|
Ho T, Fan R, Hong WW, Khian KB. Maximal mydriasis evaluation in cataract surgery. Indian J Ophthalmol 1992;40:74-8
|How to cite this URL:|
Ho T, Fan R, Hong WW, Khian KB. Maximal mydriasis evaluation in cataract surgery. Indian J Ophthalmol [serial online] 1992 [cited 2020 Apr 4];40:74-8. Available from: http://www.ijo.in/text.asp?1992/40/3/74/25767
| Introduction|| |
The size of the pupil is perhaps the most important variable in cataract surgery. Apart from opening and closing the wound, all major actions in cataract surgery takes place at or behind the plane of the pupil. It is therefore easy to appreciate how a well dilated pupil can greatly facilitate safe and precise cataract surgery. On the other hand, probably nothing disconcerts the cataract surgeon more than to have a patient wheeled into the operating room with a poorly dilated pupil.
| Rationale for the maximal mydriasis test|| |
Unfortunately, not every pupil will dilate to an optimal size even with the strongest mydriatic regimes. It is this variability in the maximal mydriatic ability of the pupil that often poses problems as for example in the aforementioned scenario of a patient wheeled into the operating room with a less than optimally dilated pupil. The surgeon then has to resolve, under pressure of time, the issue of whether the poor dilation is an idiosyncratic response or a pharmacological problem such as drops which have been instilled too early or too late.
Further stress is likely as he may also need to change his planned method of surgery, equipment needed and even choice of lens implant. For example - a planned phacoemulsification procedure may have to be abandoned in favour of an extra-capsular extraction, a planned capsulorhexis may be dropped in favour of a can-opening type capsulotomy, equipment for sphincterotomy or synechiotomy may have to be readied at the twelfth hour, a large optic IOL substituted for a smaller one. This altogether unsatisfactory state of affairs could have been avoided if an objective and reliable test of the maximal mydriatic capability of the pupil had been done when the patient first presented in the office for cataract surgery evaluation.
We appreciate that dilated pupil examination should be an integral part of a routine pre-operative cataract exam. However, even within the same office, there is often variation in the type and concentration of the drops use in the dilating regime and inconsistency in the interval period from instillation of drops to when the patient is seen. Furthermore, in most cases, the emphasis is on the fundal examination and attention is drawn to the pupil only when there is obvious pupillary miosis or synechiae. Record of the pupillary dilation is therefore not often done as it does not make much sense to record this in view of the aforementioned variables.
Therefore, we propose the Maximal Mydriasis Test (MMT) as a consistent, objective and dependable means to assess maximal pupillary dilation in the office setting and thereby provide the cataract surgeon with important pre-operative information on the idiosyncratic mydriatic behaviour of the pupil. The test is done at the time of the initial assessment for cataract surgery.
| Material and methods|| |
A series of MMTs done on 165 eyes of 100 consecutive patients referred to the Ophthalmology Department, Tan Tock Seng Hospital Singapore, for cataract assessment is presented to illustrate its practical applications and value.
The MMT is done after the history is taken and the anterior segment assessed. Contraindications for the test includes ocular history of angle closure glaucoma or a very shallow anterior chamber. The test consists of two steps. In step 1, topical anesthesia (proparacaine) is instilled followed by one drop of 1% tropicamide. This is followed after 5 mins by one drop of 2.5% phenylephrine. All drops are instilled with punctal occlusion; achieved by applying digital pressure at the inner canthal region. At 30 mins the pupil size is measured at the slit lamp (see later) and the anterior segment re-evaluated for complications as posterior synechiae, subtle lens subluxation or eccentric dilation which may complicate the performance of cataract surgery. The test stops if the measured pupil diameter equals or exceeds 8 mm. Step 2 is done on eyes with pupillary dilation less than 8 mm. It involves a repeat instillation of tropicamide 1% followed 5 mins later by one drop of 10% phenylephrine. After another 30 mins, the pupil diameter is again measured and the anterior segment evaluated. Routine fundal examination is done after the MMTto complete the ocular examination.
[Figure - 1] summarises the 2 steps.
The maximal pupil dilation recorded (measured in millimeters) is the MMT value. Measurement of the pupil size was done using the slit lamp as follows.
| Measurement of pupil size using the slit lamp|| |
The observer first adjusts both eyepieces to correct for any refractive error. The illuminating column of the slit lamp is brought to lie between the objective lenses of the microscope so that the illuminating and viewing systems are co-axial. The illuminating column is then tilted forwards one stop so that light reflected from the surface of the cornea does not enter the viewing system to cause a glare. The slit beam is adjusted to a thin slit of 1 mm width or less and focused to fall onto the pupillary plane [Figure - 2]. The length of the beam is adjusted such that both ends of the slit beam just fall on the edge of the pupil. Vertical and horizontal readings are then taken off the scale and the readings averaged and recorded as the MMT value. Where the pupil is eccentric, the largest and smallest diameters are recorded and its mean taken as the MMT value.
| Results|| |
165 eyes of 100 patients were tested. The age range was 47 to 86 years with a mean age of 64.7 yrs [Figure - 3]. There were 73 Chinese patients, 16 Malay patients and 11 Indian patients in the study population.
Of the 165 eyes tested, 58 eyes (35%) had the test terminated after Step 1 as they dilated to MMT value of 8 mm or greater. The remaining 107 eyes (65%) completed the full test.
[Figure - 4] shows the MMT values of the eyes tested. 104 or 63% of eyes dilated excellently with the protocol with 8 mm or greater MMT values. This formed the largest group. Eyes with 6 mm MMT values formed the next most frequent group at 29 or 17% of eyes. 19 or 12% of eyes had MMT values of 7 mm and were the third most common group. The remaining 13 or 8% were eyes with 5 mm or less MMT values. Causes for the very poor dilation in these eyes includes posterior synechiae (5 eyes), diabetic autonomic pupillopathy (4 eyes) rubeosis (1), pseudoexfoliative glaucoma (1) and unknown in 2 eyes.
We took arbitrarily a MMT value of 6 mm or less as indicative of poor pupil dilation for purpose of cataract surgery. There were 42 or 26% of eyes in this group. The number of diabetic eyes in this group was looked at since it is well established that diabetic pupils do not dilate as well ,. Overall, 53 of the 165 eyes were diabetic eyes. Of these diabetic eyes, 28 dilated poorly [Table - 1]. As expected, this was statistically significant (p 0.001 Chi Square Test: Yates corrected)
We also took arbitrarily a MMT value of 8 mm or more as indicative of excellent dilation for purpose of cataract surgery. There were 104 or 63% of eyes in this group. Again, the number of diabetic eyes in this group were looked at. There were only 13 diabetic eyes in this second group against 91 non-diabetic eyes. As would be expected, this was again statistically significant (p 0.001 Chi Square Test: Yates corrected).
| Discussion|| |
One of the most effective yet convenient and safe mydriatic regimes is that of a combination of topical tropicamide and phenylephrine ,, This is the regime on which the Maximal Mydriasis Test is based.
This combination has advantages of producing prompt and maximal yet transient mydriasis that would be maintained despite the intense light of the slit lamp and indirect ophthalmoscope. Both tropicamide and phenylephrine are rapidly acting with peak mydriatic effect achieved at 20 minutes from instillation. The test protocol starts with instillation of 0.5% solution of proparacaine to anaesthetise the cornea and conjunctiva. This reduces the discomfort and reflex squeezing of the lids that occurs in some patients with tropicamide and phenylephrine and prevent transport of the mydriatic drugs across the cornea ,.
In terms of safety, tropicamide is a short-acting parasympatholytic agent which has proven its safety over the years. Phenylephrine, especially in concentrations below 10% has been used safely for many years sub . Systemic toxicity from topical 10% phenylephrine causing severe acute hypertensive episodes and myocardial infarction has been reported and is a concern ,. However the protocol is not contraindicated in hypertensive or cardiac patients as only single instillations of phenylephrine drops are use. Furthermore, the 10% phenylephrine are commercial preparations which are actually equivalent to 2.25% of freshly prepared ones . As an additional safety factor, instillation was done with pu nctal occlusion to minimise systemic absorption via the nasolacrimal mucosa.
The slit lamp is used to assess pupil dilation although it is admittedly a less accurate instrument for pupillometry than the infra-red electronic pupillograph or pupillometer. However, it is a readily accessible instrument in the clinic, is relatively inexpensive and can also be used at the same time for biomicroscopy of the anterior segment.
It takes slightly more than an hour to go through the complete test (about half hour each for Steps 1 and 2). However, in this study, only 65% of the eyes need go through the complete test as the remaining 35% were easy and excellent dilators i.e. achieving MMT values of 8 mm or more with Step 1 alone. In other words, one third of the patients had the test terminated after Step 1 and only two-thirds need complete the test.
104 or 63% of eyes dilated excellently with the protocol with 8 mm or greater MMT values. 19 or 12% of eyes had 7 mm MMT values and 42 or 25% of eyes had 6 mm or less MMT values. This varied results serves to emphasise the value and importance of the maximal Mydriasis Test which will be elaborated on later. The results also appears to show a relatively low proportion of good dilators and a relatively high proportion of poor dilators as compared to pharmocology studies . The explanation is simple enough. It is well established that the mydriatic response produced by a drug is inversely proportional to the degree of iris pigmentation ,.Our study population is of entirely Asian eyes with predominance of dark brown irides and this is one contributory factor towards the high proportion of poorly dilating eyes.
Another contributory factor is the fact that diabetic pupils dilate less well than non-diabetic pupils , . The incidence of diabetic eyes in this study is relatively high (53 or 32% of eyes). This is not unexpected as the study population consists of older patients referred for cataract assessment and these patients are more prone to develop cataracts. Also, the age factor is important as the mean age of the population is 65 years and age-related miosis is another well established fact .
| Value of the mmt in cataract surgery|| |
Most of us would agree that the size of the pupil is probably the most important variable in cataract surgery as apart from opening and closing the wound, all major actions in cataract surgery takes place at or behind the plane of the pupil. The MMT has its use as a consistent, objective and dependable means to provide the cataract surgeon with important pre-operative information on the idiosyncratic maximal dilation capabilities of the pupil.
Let us again take the aforementioned common scenario where a patient is wheeled into the operating room with a less than optimally dilated pupil. Multiple questions and problems arise in this situation. Have drops been put in? If so have they been instilled too early or too late? Can I get this pupil to dilate further with additional drops? Should I change my operation plan, implant method, implant choice?
If the MMT had been done, the surgeon would be spared the surprise, know immediately whether this pupil is already dilating to its maximal ability or not and would already have an effective and appropriate plan ready. In short, much valuable time would be saved and stress avoided.
Having established the MMT values, how do we apply the information to benefit. In eyes with high MMT values or good dilation, the surgeon can appropriately and confidently plan surgical manoeuvres where wide pupillary dilation is important e.g. phacoemulsification procedure, capsulorhexis, implantation of large optic IOL. In our local context, it helps us to better target and utilise restricted costly resources like the use of viscoelastics and indomethacin drops which are mainly reserved for use in expected problem eyes.
Where MMT values are on the low side the surgeon is alert to detect abnormalities that may complicate cataract extraction like presence of posterior synechiae, subluxated lenses, eccentric pupils. Again, the surgeon can plan more effectively, appropriately and confidently. For example, an extra-capsular extraction may be preferred over a phacoemulsification procedure, a planned capsulorhexis may be dropped in favour of a can-opening capsulotomy, equipment for synechiotomy or sphincterotomy can be readied beforehand and even the choice of the lens implant e.g. a large optic IOL may have to be changed. It also enables better targeting and utilisation of certain costly items like viscoelastics and indomethacin drops which would be use in these expected problem eyes. This has significantly improved our cost-effectiveness. In the context of developing and third wo:,d countries, this is an important advantage.
Where the MMT results shows particularly poor mydriasis and where there are no systemic contraindications, we use a sub-conjunctival injection of mydricaine (atropine sulphate 1 mg, cocaine HCL 5 mg, adrenaline tartrate 10 mcg, chlorbutol 300 mcg, sodium chloride 1 mg in 2.3 ml of water) as the pre-operative dilation regime. This concoction has been found to be extremely effective in achieving that extra 1 or 2 mm dilation in most cases.
| Conclusion|| |
The MMT is a test that is safe and simple and can be easily integrated into the normal pre-operative evaluation of the patient. The varied pupillary dilation of the series of patients presented emphasise the value and importance of the MMT. We have construed numerous benefits which can be gained by the cataract surgeon and his team as well as by the hospital. The end beneficiary is however the most important and that is the patient.
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[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4]
[Table - 1], [Table - 2]