Very good!

MYDRIATICS

The pupil is the circular opening in the middle of the iris. This small hole allows the assessment of the eye fundus. However, examining the fundus through the undilated pupil might be a challenge due to the small pupil, lens opacities and abnormal retinal condition. To facilitate a more detailed inspection through the pupil, it will be necessary to dilate the pupil with mydriatics. Mydriatics are drugs which are mostly used on elderly patients due to small pupils and might be essential in any age group that suspected on having macular cyst or hole, location of a penetrating foreign body, intraocular tumours and peripheral detachment (Hopkins and Pearson, 1998). 

The physiology behind a normal pupillary constriction is a balance between two different neuromechanisms (sympathetic and parasympathetic nervous systems). The sympathetic nervous system innervated the pupil dilator muscle whereas the parasympathetic nervous system innervated the pupil sphincter muscle. Due to the antagonistic effect created by these two opponent muscles, there are two different modes of action of mydriasis. It involves either overreaction of sympathetic nervous system or undereaction of parasympathetic nervous system which leads to the pupil dilation. With the use of antimuscarinic mydriatic, it will generate cycloplegic effect on pupil sphincter muscle and able to depress the pupil light reflex.  Tropicamide, cyclopentolate, homatropine and eucatropine are four types of antimuscarinic mydriatic that have been used so far routinely. It is suggested that tropicamide would be the most preferred drugs for a quick and short duration of mydriasis (Whelan et al., 2011).

On the other hand, sympathomimetic mydriatics are other types of mechanism that will cause contraction of the pupil dilator muscle. Included in the list of sympathomimetic drugs are phenylephrine, cocaine, hydroxyamphetamine and ephedrine hydrochloride. However, phenylephrine is the only sympathomimetic drugs that clinically relevance for routine mydriasis. The existence of these two mechanisms has leads to the comparative studies on different types of mydriatics. An ideally used mydriatic will possess quick onset of action and recovery with less side effects. Park et al. (2009) found that 1% tropicamide produce better pupil dilation than 2.5% phenylephrine. However, the mixture of 1% tropicamide with 2.5% phenylephrine demonstrates more effective reaction compared to multiple drops of single mydriatic. Additionally, Paggriano et al. (1993) suggested that the combination of 0.5% tropicamide and 2.5% phenylephrine has the ability to induce rapid and maximum pupil dilation rather than tropicamide alone.  It is also believed that the sufficiently dilated pupil can be produced by the combination of reduced concentration of mydriatics drugs (Krumholdz et al., 2006). Hence, for an appreciable mydriasis with sufficient depth, mixtures of antimuscarinic and sympathomimetic may be used.

While applying an ophthalmic drug, there is always a possibility of generating adverse effects. Side effects of mydriatics can be induced either on the eyes or on the body. Generally speaking, dilated patients may suffer adverse effects such as glare (due to paralysed response to light), blurred vision and stinging that last for several hours. For that reason, patient should be advised to wear sunglass afterwards to reduce glare (Brunner et al., 2009). Myth believes that the contraction of iris sphincter gives rise to increased intraocular pressure (IOP), hence glaucoma may be precipitated. Numerous studies have researched regarding this issue and eventually lead to an argument. Pandit and Taylor (2000) concluded that the instillation of tropicamide alone does not induce any risks even in the patient with chronic glaucoma. Conversely, Stadtbaulmer et al. (2006) dilated 10 adult normal feline with 10% phenylephrine, 0.5% tropicamide, 1% cyclopentolate and 1% atropine. The IOP and pupil size were then measured. They found that parasympatholytics of 1% atropine, 1% cyclopentolate and 0.5% tropicamide caused increase in IOP and pupil size but sympathomimetic of 10% phenylephrine show no significant changes in either IOP or pupil size.  Wolfs et al. (1997) tested subjects aged 55 years and over with 0.5% tropicamide and 5% phenylephrine. They concluded that 3 in every 10000 subjects are likely to induce an attack of closed angle glaucoma after diagnostic mydriasis. In order to minimize these adverse effect, 1 drop of 0.5% tropicamide followed by 1 drop of 2.5% phenylephrine may ideally use (Levine ,1985).

There has been some discussion on the systemic effects that produce by sympathomimetic mydriatics. Topically administered sympathomimetics agents have a direct positive chronotropic effect on heart rate and elevation of systolic and diastolic blood pressure. Premature infant is the one most sensitive to this effect. Laws et al. (1996) suggested that the elevation of blood pressure may due to the topical mydriasis but the later changes on the pulse rate may represent the additional stress response. Ogut et al. (1996) found that 2.5% phenylephrine gives maximum side effects while 1% tropicamide gives minimum side effects towards infants. Bolt et al. (1992) recommend the combination of 2.5% phenylephrine and 0.5% tropicamide in order to maximize the pupil dilation without inducing any adverse effect in infants. In addition, Elibol et al. (1997) concluded that reducing the mydriatics drop size can inhibit possible side effects thus confirming the fact that standard drops produce significant side effects.  Therefore, it is important for optometrist to take into consideration with the use of sympathomimetic drugs in patients with cardiac disease, hypertension, aneurysms and arteriosclerosis.

There are several factors that may affect the pupil dilation. One of the main factors is ocular pathology. It is believed that pupils become less responsive in patients with diabetes mellitus. Lei et al. (2011) dilated 107 eyes in patients with no apparent diabetic retinopathy and patient with diabetic retinopathy. They found that long-term diabetic patients responded poorly to pharmacological mydriasis compared to nondiabetic patients. Larkin et al. (1989) have also carried out a comparative study on different concentrations of tropicamide (0.05%, 0.1%, 0.25% and 0.5%) combined with hydroxyamphetamine 1%. They found that there is no significant difference on pupil diameter but various concentrations showed significant difference in terms of inhibition of responsiveness to light and minimal paralysis of accommodation. With the use of phenylephrine alone, Suwan-Apichon et al. (2010) suggested that 10% of phenylephrine is an ideal concentration rather than 2.5% of phenylephrine.

Mydriatics may precipitate acute glaucoma in the over-60s with shallow anterior chambers particularly if there is a strong family history of glaucoma. Wolfs et al. (1997) found that 2% of nonselected subjects of 55 years old age or older have high risk on inducing acute angle-closure glaucoma thus concluded that age was a significant factor. Another possible factor that might affect the mydriasis is iris pigmentation. For example, Patil et al. (1972) proposed that highly pigmented iris will absorbed large amount of drugs and relative binding of drugs lead to fewer drugs available for the interactions with adrenergic neurons. Consequently, reducing the mydriatic effect in highly pigmented iris compared to light pigmented iris. To deal with these various factors, Cooper et al. (1996) suggested that paremyd would be the most preferred agents due to its effectivity without introducing side effects and also independent of age, iris color or skin color.

                    

       Obviously, it is essential for a practitioner to be aware of any clinical signs and symptoms of such an attack produced by mydriatics and always consider the appropriateness of mydriatic on patient’s condition to prevent any side effects that may occur.

Written by,

NURUL SYAHIDA BINTI MOHD SAHRI

copy and paste report ni dlm blog for security reason ;b

purely researched and written by me

tanpa bantuan mat2 salleh utk check grammar aku..heheh

and Alhamdulillah there were only 2 grammar mistakes spotted by my lecturer

mcm x percaya weh! 

coz sblum ni report aku mmg byk gila kena tegur psl grammar mistakes =.="
dah mcm kertas pekse nobita jek report aku dlu..pnuh dgn red ink

and Alhamdulillah again coz got a "very good" mark for this report!

report2 sblum ni mmg la ade je dpt "very good" 

tp bukn nye sepenuh nye ditulis oleh aku

ade la jgk mat salleh tlg correct and rephrase blik ayat2 aku ;b

sbb tu sblum ni klu dpt "very good" tu aku x heran sgt...kuikuikui

tp kali ni pure dtg dr aku..mase tgk markah report ni, aku rase mcm tgh pegang emas! walla!

I'll keep this report for the rest of my life~letak dlm blog mmg dijamin xkn hilang! muahahaha

Salam :)