Disorders of the Lens: Introduction

00:01 We will visit the anatomy once more.

00:04 So now as you can see each picture here we're looking at common pathologies in different parts of the eye.

00:10 So far we've talked about the conjunctiva, well, from the outer to in we talked about the eyelid then issues in the conjunctiva and the cornea a little bit and then here we'll take a look at issues in the lens.

00:22 Lens, so what do you think the number one pathology that I'm gonna show you is? How about this? That's cataract.

00:32 In Greek, cataractos, means waterfall.

00:36 What does it have to do with this? If you take a look at a waterfall and you see the water falling of the rock or whatnot, what color is it? Opaque, white.

00:47 Take a look at the lens here.

00:49 It's become, yes, opaque.

00:52 There are different causes here.

00:53 I need to make sure that we go through this.

00:55 So we divide cataracts into acquired and congenital, okay? Acquired and congenital.

01:00 Where's my issue? Lens.

01:03 What do you think the number one cause is in the US? Age, okay.

01:08 So as we get older we can then accumulate toxins and such.

01:12 For example, maybe it's a sorbitol especially diabetes and then may then cause cataracts and eventually may result in blindness, so no joke.

01:22 Waterfall.

01:25 Cataract.

01:26 So acquired causes, number one cause increasing age, increasing age, increasing age.

01:36 You wanna focus on that.

01:38 Other acquired causes, smoking, excessive alcohol consumption, once again, excessive UV exposure, prolonged corticosteroid use, diabetes.

01:51 Remember in diabetes, we have the aldose reductase pathway and so therefore, may produce too much sorbitol accumulating in the lens, right, giving you cataract.

02:01 Keep the lens separate from the pathologies then we'll take a look at in the retina.

02:05 Trauma, infection, acquired causes.

02:08 Next, we'll take a look at congenital.

02:11 Now under congenital I want you to stop getting in the hand but I've just listing things up.

02:16 The infections and such in micro long list, but in micro I think we've talked about enough pathologies there where you can maneuver properly but biochemistry might be a different story and I find in my experience that biochemistry, especially with pathology, often times there's a weak link.

02:32 Let me ask you a question between classic galactosemia and the galactokinase deficiency.

02:40 The question is what the heck is accumulating in this biochemical pathologies that is then resulting in congenital cataract accumulation or presentation? Question, so what is the most common or what is accumulating in classic galactosemia or galactokinase deficiency? Is the question then giving rise to a cataract in this child, right? Child! You talk about a cataract in a newborn? Wow, let's take a look at what's happening here.

03:16 Which one are you gonna focus on for, let's say, more purposes the classic galactosemia.

03:21 Do you remember the name of the enzyme? Let me walk you through something that you find to be interesting for biochemistry, you ready? All I ever do is to make sure that I give you information that's relevant to your practice and to your boards so trust me on this.

03:36 Let's walk through what's happening.

03:38 So let's say that you had ice cream.

03:41 Hmm, that's dairy and with ice cream that's been given to this, let's say, baby? oh my goodness gracious there's accumulation of some substrate in the lens which is then giving rise to cataract in this newborn.

03:58 So you wanna avoid giving ice cream.

04:00 What is going on in this patient? We're not talking about lactose intolerance.

04:03 Do not jump to that.

04:05 A lot of students will do that, right? For example, I'm getting older, my requirement for calcium is not as high as what it used to be.

04:12 How do I know? Because when I have ice cream, guess where I am? I'm on the toilet and I have massive diarrhea because I have lactose intolerance, right? That is not what this baby is having.

04:23 Is that understood? So what is the baby having? Well, when you take ice cream it's lactose, isn't it? There's lactose.

04:32 Over to the far right, lactose is a combination of glucose and over to the far left, the lactose'you know that lactose is a disaccharide and metabolite of dairy.

04:48 Let's continue as a newborn.

04:51 So you know glucose will be converting to glucose-6-phosphate? I don't wanna spend too much time here? just a couple of enzymes there that you wanna know for sure.

04:59 If you're moving through glycolysis then you have glucokinase and hexokinase.

05:04 Remind me which one of these enzymes will be located in the liver? So what happens when you're taking in a dairy product in a patient that you expect to have maybe classic galactosemia? And that's where our focus will be on.

05:18 We also do have the galactokinase deficiency but let's focus in classic galactosemia.

05:23 Now be careful here, a lot of med students and residents then get confused with ice cream and thinking it's a dairy and thinking that it's lactose intolerance.

05:32 Well, as we get older or let's say that is an African population or Asian population or the Native American population, it might be lactase deficiency.

05:43 That's lactose intolerance and so therefore, soon after consuming ice cream where is that patient? On the toilet or lactoflatulence, right? That's lactose intolerance but that's a lot different than what's happening here in the newborn.

05:58 Now when you can see an ice cream or a dairy product which is lactose which is a disaccharide, the combination of both the glucose and galactose, is it not? And the brush border enzymes responsible for breaking this down.